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## C/C++ Interface For SQLite Version 3

This page defined the C-language interface to SQLite. This page is intended as a reference to what SQLite is suppose to do. This is not a tutorial. This page is designed to be precise, not easy to read.

This page contains all C-language interface information in a single HTML file. The same information is also available broken out into lots of small pages for easier viewing, if you prefer.

This document is created by a script which scans comments in the source code files.

## Objects:

sqlite3 sqlite3_int64 sqlite3_uint64 sqlite_int64 sqlite_uint64 | sqlite3_file sqlite3_io_methods sqlite3_mutex sqlite3_vfs sqlite3_stmt | sqlite3_value sqlite3_context sqlite3_temp_directory sqlite3_blob

## Constants:

SQLITE_ABORT SQLITE_ACCESS_EXISTS SQLITE_ACCESS_READ SQLITE_ACCESS_READWRITE SQLITE_ALTER_TABLE SQLITE_ANALYZE SQLITE_ANY SQLITE_ATTACH SQLITE_AUTH SQLITE_BLOB SQLITE_BUSY SQLITE_CANTOPEN SQLITE_CONSTRAINT SQLITE_COPY SQLITE_CORRUPT SQLITE_CREATE_INDEX SQLITE_CREATE_TABLE SQLITE_CREATE_TEMP_INDEX SQLITE_CREATE_TEMP_TABLE SQLITE_CREATE_TEMP_TRIGGER SQLITE_CREATE_TEMP_VIEW SQLITE_CREATE_TRIGGER SQLITE_CREATE_VIEW SQLITE_CREATE_VTABLE SQLITE_DELETE SQLITE_DENY SQLITE_DETACH SQLITE_DONE SQLITE_DROP_INDEX SQLITE_DROP_TABLE SQLITE_DROP_TEMP_INDEX SQLITE_DROP_TEMP_TABLE SQLITE_DROP_TEMP_TRIGGER SQLITE_DROP_TEMP_VIEW SQLITE_DROP_TRIGGER SQLITE_DROP_VIEW SQLITE_DROP_VTABLE SQLITE_EMPTY SQLITE_ERROR SQLITE_FCNTL_LOCKSTATE SQLITE_FLOAT SQLITE_FORMAT SQLITE_FULL SQLITE_FUNCTION SQLITE_IGNORE SQLITE_INSERT SQLITE_INTEGER SQLITE_INTERNAL SQLITE_INTERRUPT SQLITE_IOCAP_ATOMIC SQLITE_IOCAP_ATOMIC16K SQLITE_IOCAP_ATOMIC1K SQLITE_IOCAP_ATOMIC2K SQLITE_IOCAP_ATOMIC32K SQLITE_IOCAP_ATOMIC4K SQLITE_IOCAP_ATOMIC512 SQLITE_IOCAP_ATOMIC64K SQLITE_IOCAP_ATOMIC8K SQLITE_IOCAP_SAFE_APPEND SQLITE_IOCAP_SEQUENTIAL SQLITE_IOERR SQLITE_IOERR_BLOCKED SQLITE_IOERR_DELETE SQLITE_IOERR_DIR_FSYNC SQLITE_IOERR_FSTAT SQLITE_IOERR_FSYNC SQLITE_IOERR_NOMEM SQLITE_IOERR_RDLOCK | SQLITE_IOERR_READ SQLITE_IOERR_SHORT_READ SQLITE_IOERR_TRUNCATE SQLITE_IOERR_UNLOCK SQLITE_IOERR_WRITE SQLITE_LOCKED SQLITE_LOCK_EXCLUSIVE SQLITE_LOCK_NONE SQLITE_LOCK_PENDING SQLITE_LOCK_RESERVED SQLITE_LOCK_SHARED SQLITE_MISMATCH SQLITE_MISUSE SQLITE_MUTEX_FAST SQLITE_MUTEX_RECURSIVE SQLITE_MUTEX_STATIC_LRU SQLITE_MUTEX_STATIC_MASTER SQLITE_MUTEX_STATIC_MEM SQLITE_MUTEX_STATIC_MEM2 SQLITE_MUTEX_STATIC_PRNG SQLITE_NOLFS SQLITE_NOMEM SQLITE_NOTADB SQLITE_NOTFOUND SQLITE_NULL SQLITE_OK SQLITE_OPEN_CREATE SQLITE_OPEN_DELETEONCLOSE SQLITE_OPEN_EXCLUSIVE SQLITE_OPEN_MAIN_DB SQLITE_OPEN_MAIN_JOURNAL SQLITE_OPEN_MASTER_JOURNAL SQLITE_OPEN_READONLY SQLITE_OPEN_READWRITE SQLITE_OPEN_SUBJOURNAL SQLITE_OPEN_TEMP_DB SQLITE_OPEN_TEMP_JOURNAL SQLITE_OPEN_TRANSIENT_DB SQLITE_PERM SQLITE_PRAGMA SQLITE_PROTOCOL SQLITE_RANGE SQLITE_READ SQLITE_READONLY SQLITE_REINDEX SQLITE_ROW SQLITE_SCHEMA SQLITE_SELECT SQLITE_STATIC SQLITE_SYNC_DATAONLY SQLITE_SYNC_FULL SQLITE_SYNC_NORMAL SQLITE_TESTCTRL_FAULT_BENIGN_FAILURES SQLITE_TESTCTRL_FAULT_CONFIG SQLITE_TESTCTRL_FAULT_FAILURES SQLITE_TESTCTRL_FAULT_PENDING SQLITE_TEXT SQLITE_TOOBIG SQLITE_TRANSACTION SQLITE_TRANSIENT SQLITE_UPDATE SQLITE_UTF16 SQLITE_UTF16BE SQLITE_UTF16LE SQLITE_UTF16_ALIGNED SQLITE_UTF8 SQLITE_VERSION SQLITE_VERSION_NUMBER

## Functions:

sqlite3_aggregate_context sqlite3_aggregate_count sqlite3_auto_extension sqlite3_bind_blob sqlite3_bind_double sqlite3_bind_int sqlite3_bind_int64 sqlite3_bind_null sqlite3_bind_parameter_count sqlite3_bind_parameter_index sqlite3_bind_parameter_name sqlite3_bind_text sqlite3_bind_text16 sqlite3_bind_value sqlite3_bind_zeroblob sqlite3_blob_bytes sqlite3_blob_close sqlite3_blob_open sqlite3_blob_read sqlite3_blob_write sqlite3_busy_handler sqlite3_busy_timeout sqlite3_changes sqlite3_clear_bindings sqlite3_close sqlite3_collation_needed sqlite3_collation_needed16 sqlite3_column_blob sqlite3_column_bytes sqlite3_column_bytes16 sqlite3_column_count sqlite3_column_database_name sqlite3_column_database_name16 sqlite3_column_decltype sqlite3_column_decltype16 sqlite3_column_double sqlite3_column_int sqlite3_column_int64 sqlite3_column_name sqlite3_column_name16 sqlite3_column_origin_name sqlite3_column_origin_name16 sqlite3_column_table_name sqlite3_column_table_name16 sqlite3_column_text sqlite3_column_text16 sqlite3_column_type sqlite3_column_value sqlite3_commit_hook sqlite3_complete sqlite3_complete16 | sqlite3_create_collation sqlite3_create_collation16 sqlite3_create_collation_v2 sqlite3_create_function sqlite3_create_function16 sqlite3_data_count sqlite3_db_handle sqlite3_enable_load_extension sqlite3_enable_shared_cache sqlite3_errcode sqlite3_errmsg sqlite3_errmsg16 sqlite3_exec sqlite3_expired sqlite3_extended_result_codes sqlite3_file_control sqlite3_finalize sqlite3_free sqlite3_free_table sqlite3_get_autocommit sqlite3_get_auxdata sqlite3_get_table sqlite3_global_recover sqlite3_interrupt sqlite3_last_insert_rowid sqlite3_libversion sqlite3_libversion_number sqlite3_load_extension sqlite3_malloc sqlite3_memory_alarm sqlite3_memory_highwater sqlite3_memory_used sqlite3_mprintf sqlite3_mutex_alloc sqlite3_mutex_enter sqlite3_mutex_free sqlite3_mutex_held sqlite3_mutex_leave sqlite3_mutex_notheld sqlite3_mutex_try sqlite3_open sqlite3_open16 sqlite3_open_v2 sqlite3_prepare sqlite3_prepare16 sqlite3_prepare16_v2 sqlite3_prepare_v2 sqlite3_profile sqlite3_progress_handler sqlite3_realloc sqlite3_release_memory | sqlite3_reset sqlite3_reset_auto_extension sqlite3_result_blob sqlite3_result_double sqlite3_result_error sqlite3_result_error16 sqlite3_result_error_code sqlite3_result_error_nomem sqlite3_result_error_toobig sqlite3_result_int sqlite3_result_int64 sqlite3_result_null sqlite3_result_text sqlite3_result_text16 sqlite3_result_text16be sqlite3_result_text16le sqlite3_result_value sqlite3_result_zeroblob sqlite3_rollback_hook sqlite3_set_authorizer sqlite3_set_auxdata sqlite3_sleep sqlite3_snprintf sqlite3_soft_heap_limit sqlite3_step sqlite3_table_column_metadata sqlite3_test_control sqlite3_thread_cleanup sqlite3_threadsafe sqlite3_total_changes sqlite3_trace sqlite3_transfer_bindings sqlite3_update_hook sqlite3_user_data sqlite3_value_blob sqlite3_value_bytes sqlite3_value_bytes16 sqlite3_value_double sqlite3_value_int sqlite3_value_int64 sqlite3_value_numeric_type sqlite3_value_text sqlite3_value_text16 sqlite3_value_text16be sqlite3_value_text16le sqlite3_value_type sqlite3_version sqlite3_vfs_find sqlite3_vfs_register sqlite3_vfs_unregister sqlite3_vmprintf

## Standard File Control Opcodes

>     #define SQLITE_FCNTL_LOCKSTATE        1

These integer constants are opcodes for the xFileControl method of the sqlite3_io_methods object and to the sqlite3_file_control() interface.

The SQLITE_FCNTL_LOCKSTATE opcode is used for debugging. This opcode cases the xFileControl method to write the current state of the lock (one of SQLITE_LOCK_NONE, SQLITE_LOCK_SHARED, SQLITE_LOCK_RESERVED, SQLITE_LOCK_PENDING, or SQLITE_LOCK_EXCLUSIVE) into an integer that the pArg argument points to. This capability is used during testing and only needs to be supported when SQLITE_TEST is defined.

## A Handle To An Open BLOB

>     typedef struct sqlite3_blob sqlite3_blob;

An instance of the following opaque structure is used to represent an blob-handle. A blob-handle is created by sqlite3_blob_open() and destroyed by sqlite3_blob_close(). The sqlite3_blob_read() and sqlite3_blob_write() interfaces can be used to read or write small subsections of the blob. The sqlite3_blob_bytes() interface returns the size of the blob in bytes.

## SQL Function Context Object

>     typedef struct sqlite3_context sqlite3_context;

The context in which an SQL function executes is stored in an sqlite3_context object. A pointer to an sqlite3_context object is always first parameter to application-defined SQL functions.

## OS Interface Open File Handle

>     typedef struct sqlite3_file sqlite3_file;
>     struct sqlite3_file {
>       const struct sqlite3_io_methods *pMethods;  /* Methods for an open file */
>     };

An sqlite3_file object represents an open file in the OS interface layer. Individual OS interface implementations will want to subclass this object by appending additional fields for their own use. The pMethods entry is a pointer to an sqlite3_io_methods object that defines methods for performing I/O operations on the open file.

## OS Interface File Virtual Methods Object

>     typedef struct sqlite3_io_methods sqlite3_io_methods;
>     struct sqlite3_io_methods {
>       int iVersion;
>       int (*xClose)(sqlite3_file*);
>       int (*xRead)(sqlite3_file*, void*, int iAmt, sqlite3_int64 iOfst);
>       int (*xWrite)(sqlite3_file*, const void*, int iAmt, sqlite3_int64 iOfst);
>       int (*xTruncate)(sqlite3_file*, sqlite3_int64 size);
>       int (*xSync)(sqlite3_file*, int flags);
>       int (*xFileSize)(sqlite3_file*, sqlite3_int64 *pSize);
>       int (*xLock)(sqlite3_file*, int);
>       int (*xUnlock)(sqlite3_file*, int);
>       int (*xCheckReservedLock)(sqlite3_file*);
>       int (*xFileControl)(sqlite3_file*, int op, void *pArg);
>       int (*xSectorSize)(sqlite3_file*);
>       int (*xDeviceCharacteristics)(sqlite3_file*);
>       /* Additional methods may be added in future releases */
>     };

Every file opened by the sqlite3_vfs xOpen method contains a pointer to an instance of the this object. This object defines the methods used to perform various operations against the open file.

The flags argument to xSync may be one of SQLITE_SYNC_NORMAL or SQLITE_SYNC_FULL. The first choice is the normal fsync(). OS-X style fullsync. The SQLITE_SYNC_DATA flag may be ORed in to indicate that only the data of the file and not its inode needs to be synced.

The integer values to xLock() and xUnlock() are one of

- SQLITE_LOCK_NONE,
- SQLITE_LOCK_SHARED,
- SQLITE_LOCK_RESERVED,
- SQLITE_LOCK_PENDING, or
- SQLITE_LOCK_EXCLUSIVE.

xLock() increases the lock. xUnlock() decreases the lock. The xCheckReservedLock() method looks to see if any database connection, either in this process or in some other process, is holding an RESERVED, PENDING, or EXCLUSIVE lock on the file. It returns true if such a lock exists and false if not.

The xFileControl() method is a generic interface that allows custom VFS implementations to directly control an open file using the sqlite3_file_control() interface. The second "op" argument is an integer opcode. The third argument is a generic pointer which is intended to be a pointer to a structure that may contain arguments or space in which to write return values. Potential uses for xFileControl() might be functions to enable blocking locks with timeouts, to change the locking strategy (for example to use dot-file locks), to inquire about the status of a lock, or to break stale locks. The SQLite core reserves opcodes less than 100 for its own use. A list of opcodes less than 100 is available. Applications that define a custom xFileControl method should use opcodes greater than 100 to avoid conflicts.

The xSectorSize() method returns the sector size of the device that underlies the file. The sector size is the minimum write that can be performed without disturbing other bytes in the file. The xDeviceCharacteristics() method returns a bit vector describing behaviors of the underlying device:

- SQLITE_IOCAP_ATOMIC
- SQLITE_IOCAP_ATOMIC512
- SQLITE_IOCAP_ATOMIC1K
- SQLITE_IOCAP_ATOMIC2K
- SQLITE_IOCAP_ATOMIC4K
- SQLITE_IOCAP_ATOMIC8K
- SQLITE_IOCAP_ATOMIC16K
- SQLITE_IOCAP_ATOMIC32K
- SQLITE_IOCAP_ATOMIC64K
- SQLITE_IOCAP_SAFE_APPEND
- SQLITE_IOCAP_SEQUENTIAL

The SQLITE_IOCAP_ATOMIC property means that all writes of any size are atomic. The SQLITE_IOCAP_ATOMICnnn values mean that writes of blocks that are nnn bytes in size and are aligned to an address which is an integer multiple of nnn are atomic. The SQLITE_IOCAP_SAFE_APPEND value means that when data is appended to a file, the data is appended first then the size of the file is extended, never the other way around. The SQLITE_IOCAP_SEQUENTIAL property means that information is written to disk in the same order as calls to xWrite().

## Mutex Handle

>     typedef struct sqlite3_mutex sqlite3_mutex;

The mutex module within SQLite defines sqlite3_mutex to be an abstract type for a mutex object. The SQLite core never looks at the internal representation of an sqlite3_mutex. It only deals with pointers to the sqlite3_mutex object.

Mutexes are created using sqlite3_mutex_alloc().

## Name Of The Folder Holding Temporary Files

>     SQLITE_EXTERN char *sqlite3_temp_directory;

If this global variable is made to point to a string which is the name of a folder (a.ka. directory), then all temporary files created by SQLite will be placed in that directory. If this variable is NULL pointer, then SQLite does a search for an appropriate temporary file directory.

It is not safe to modify this variable once a database connection has been opened. It is intended that this variable be set once as part of process initialization and before any SQLite interface routines have been call and remain unchanged thereafter.

## Dynamically Typed Value Object

>     typedef struct Mem sqlite3_value;

SQLite uses the sqlite3_value object to represent all values that are or can be stored in a database table. SQLite uses dynamic typing for the values it stores. Values stored in sqlite3_value objects can be be integers, floating point values, strings, BLOBs, or NULL.

## OS Interface Object

>     typedef struct sqlite3_vfs sqlite3_vfs;
>     struct sqlite3_vfs {
>       int iVersion;            /* Structure version number */
>       int szOsFile;            /* Size of subclassed sqlite3_file */
>       int mxPathname;          /* Maximum file pathname length */
>       sqlite3_vfs *pNext;      /* Next registered VFS */
>       const char *zName;       /* Name of this virtual file system */
>       void *pAppData;          /* Pointer to application-specific data */
>       int (*xOpen)(sqlite3_vfs*, const char *zName, sqlite3_file*,
>                    int flags, int *pOutFlags);
>       int (*xDelete)(sqlite3_vfs*, const char *zName, int syncDir);
>       int (*xAccess)(sqlite3_vfs*, const char *zName, int flags);
>       int (*xGetTempname)(sqlite3_vfs*, int nOut, char *zOut);
>       int (*xFullPathname)(sqlite3_vfs*, const char *zName, int nOut, char *zOut);
>       void *(*xDlOpen)(sqlite3_vfs*, const char *zFilename);
>       void (*xDlError)(sqlite3_vfs*, int nByte, char *zErrMsg);
>       void *(*xDlSym)(sqlite3_vfs*,void*, const char *zSymbol);
>       void (*xDlClose)(sqlite3_vfs*, void*);
>       int (*xRandomness)(sqlite3_vfs*, int nByte, char *zOut);
>       int (*xSleep)(sqlite3_vfs*, int microseconds);
>       int (*xCurrentTime)(sqlite3_vfs*, double*);
>       /* New fields may be appended in figure versions.  The iVersion
>       ** value will increment whenever this happens. */
>     };

An instance of this object defines the interface between the SQLite core and the underlying operating system. The "vfs" in the name of the object stands for "virtual file system".

The iVersion field is initially 1 but may be larger for future versions of SQLite. Additional fields may be appended to this object when the iVersion value is increased.

The szOsFile field is the size of the subclassed sqlite3_file structure used by this VFS. mxPathname is the maximum length of a pathname in this VFS.

Registered vfs modules are kept on a linked list formed by the pNext pointer. The sqlite3_vfs_register() and sqlite3_vfs_unregister() interfaces manage this list in a thread-safe way. The sqlite3_vfs_find() interface searches the list.

The pNext field is the only fields in the sqlite3_vfs structure that SQLite will ever modify. SQLite will only access or modify this field while holding a particular static mutex. The application should never modify anything within the sqlite3_vfs object once the object has been registered.

The zName field holds the name of the VFS module. The name must be unique across all VFS modules.

SQLite will guarantee that the zFilename string passed to xOpen() is a full pathname as generated by xFullPathname() and that the string will be valid and unchanged until xClose() is called. So the sqlite3_file can store a pointer to the filename if it needs to remember the filename for some reason.

The flags argument to xOpen() includes all bits set in the flags argument to sqlite3_open_v2(). Or if sqlite3_open() or sqlite3_open16() is used, then flags includes at least SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE. If xOpen() opens a file read-only then it sets *pOutFlags to include SQLITE_OPEN_READONLY. Other bits in *pOutFlags may be set.

SQLite will also add one of the following flags to the xOpen() call, depending on the object being opened:

- SQLITE_OPEN_MAIN_DB
- SQLITE_OPEN_MAIN_JOURNAL
- SQLITE_OPEN_TEMP_DB
- SQLITE_OPEN_TEMP_JOURNAL
- SQLITE_OPEN_TRANSIENT_DB
- SQLITE_OPEN_SUBJOURNAL
- SQLITE_OPEN_MASTER_JOURNAL

The file I/O implementation can use the object type flags to changes the way it deals with files. For example, an application that does not care about crash recovery or rollback, might make the open of a journal file a no-op. Writes to this journal are also a no-op. Any attempt to read the journal return SQLITE_IOERR. Or the implementation might recognize the a database file will be doing page-aligned sector reads and writes in a random order and set up its I/O subsystem accordingly.

SQLite might also add one of the following flags to the xOpen method:

- SQLITE_OPEN_DELETEONCLOSE
- SQLITE_OPEN_EXCLUSIVE

The SQLITE_OPEN_DELETEONCLOSE flag means the file should be deleted when it is closed. The SQLITE_OPEN_DELETEONCLOSE will be set for TEMP databases, journals and for subjournals. The SQLITE_OPEN_EXCLUSIVE flag means the file should be opened for exclusive access. This flag is set for all files except for the main database file.

At least szOsFile bytes of memory is allocated by SQLite to hold the sqlite3_file structure passed as the third argument to xOpen. The xOpen method does not have to allocate the structure; it should just fill it in.

The flags argument to xAccess() may be SQLITE_ACCESS_EXISTS to test for the existance of a file, or SQLITE_ACCESS_READWRITE to test to see if a file is readable and writable, or SQLITE_ACCESS_READ to test to see if a file is at least readable. The file can be a directory.

SQLite will always allocate at least mxPathname+1 byte for the output buffers for xGetTempname and xFullPathname. The exact size of the output buffer is also passed as a parameter to both methods. If the output buffer is not large enough, SQLITE_CANTOPEN should be returned. As this is handled as a fatal error by SQLite, vfs implementations should endeavor to prevent this by setting mxPathname to a sufficiently large value.

The xRandomness(), xSleep(), and xCurrentTime() interfaces are not strictly a part of the filesystem, but they are included in the VFS structure for completeness. The xRandomness() function attempts to return nBytes bytes of good-quality randomness into zOut. The return value is the actual number of bytes of randomness obtained. The xSleep() method cause the calling thread to sleep for at least the number of microseconds given. The xCurrentTime() method returns a Julian Day Number for the current date and time.

## Obtain Aggregate Function Context

>     void *sqlite3_aggregate_context(sqlite3_context*, int nBytes);

The implementation of aggregate SQL functions use this routine to allocate a structure for storing their state. The first time the sqlite3_aggregate_context() routine is is called for a particular aggregate, SQLite allocates nBytes of memory zeros that memory, and returns a pointer to it. On second and subsequent calls to sqlite3_aggregate_context() for the same aggregate function index, the same buffer is returned. The implementation of the aggregate can use the returned buffer to accumulate data.

SQLite automatically frees the allocated buffer when the aggregate query concludes.

The first parameter should be a copy of the SQL function context that is the first parameter to the callback routine that implements the aggregate function.

This routine must be called from the same thread in which the aggregate SQL function is running.

## Make Arrangements To Automatically Load An Extension

>     int sqlite3_auto_extension(void *xEntryPoint);

This function registers an extension entry point that is automatically invoked whenever a new database connection is opened using sqlite3_open(), sqlite3_open16(), or sqlite3_open_v2().

This API can be invoked at program startup in order to register one or more statically linked extensions that will be available to all new database connections.

Duplicate extensions are detected so calling this routine multiple times with the same extension is harmless.

This routine stores a pointer to the extension in an array that is obtained from sqlite_malloc(). If you run a memory leak checker on your program and it reports a leak because of this array, then invoke sqlite3_reset_auto_extension() prior to shutdown to free the memory.

Automatic extensions apply across all threads.

This interface is experimental and is subject to change or removal in future releases of SQLite.

## Number Of SQL Parameters

>     int sqlite3_bind_parameter_count(sqlite3_stmt*);

This routine can be used to find the number of SQL parameters in a prepared statement. SQL parameters are tokens of the form "?", "?NNN", ":AAA", "$AAA", or "@AAA" that serve as place-holders for values that are bound to the parameters at a later time.

This routine actually returns the index of the largest parameter. For all forms except ?NNN, this will correspond to the number of unique parameters. If parameters of the ?NNN are used, there may be gaps in the list.

See also: sqlite3_bind(), sqlite3_bind_parameter_name(), and sqlite3_bind_parameter_index().

### Invariants:

F13601 | The sqlite3_bind_parameter_count(S) interface returns the largest index of all SQL parameters in the prepared statement S, or 0 if S contains no SQL parameters.

## Index Of A Parameter With A Given Name

>     int sqlite3_bind_parameter_index(sqlite3_stmt*, const char *zName);

Return the index of an SQL parameter given its name. The index value returned is suitable for use as the second parameter to sqlite3_bind(). A zero is returned if no matching parameter is found. The parameter name must be given in UTF-8 even if the original statement was prepared from UTF-16 text using sqlite3_prepare16_v2().

See also: sqlite3_bind(), sqlite3_bind_parameter_count(), and sqlite3_bind_parameter_index().

### Invariants:

F13641 | The sqlite3_bind_parameter_index(S,N) interface returns the index of SQL parameter in prepared statement S whose name matches the UTF-8 string N, or 0 if there is no match.

## Name Of A Host Parameter

>     const char *sqlite3_bind_parameter_name(sqlite3_stmt*, int);

This routine returns a pointer to the name of the n-th SQL parameter in a prepared statement. SQL parameters of the form ":AAA" or "@AAA" or "$AAA" have a name which is the string ":AAA" or "@AAA" or "$VVV". In other words, the initial ":" or "$" or "@" is included as part of the name. Parameters of the form "?" or "?NNN" have no name.

The first host parameter has an index of 1, not 0.

If the value n is out of range or if the n-th parameter is nameless, then NULL is returned. The returned string is always in the UTF-8 encoding even if the named parameter was originally specified as UTF-16 in sqlite3_prepare16() or sqlite3_prepare16_v2().

See also: sqlite3_bind(), sqlite3_bind_parameter_count(), and sqlite3_bind_parameter_index().

### Invariants:

F13621 | The sqlite3_bind_parameter_name(S,N) interface returns a UTF-8 rendering of the name of the SQL parameter in prepared statement S having index N, or NULL if there is no SQL parameter with index N or if the parameter with index N is an anonymous parameter "?" or a numbered parameter "?NNN".

## Return The Size Of An Open BLOB

>     int sqlite3_blob_bytes(sqlite3_blob *);

Return the size in bytes of the blob accessible via the open blob-handle passed as an argument.

## Close A BLOB Handle

>     int sqlite3_blob_close(sqlite3_blob *);

Close an open blob handle.

Closing a BLOB shall cause the current transaction to commit if there are no other BLOBs, no pending prepared statements, and the database connection is in autocommit mode. If any writes were made to the BLOB, they might be held in cache until the close operation if they will fit. Closing the BLOB often forces the changes out to disk and so if any I/O errors occur, they will likely occur at the time when the BLOB is closed. Any errors that occur during closing are reported as a non-zero return value.

The BLOB is closed unconditionally. Even if this routine returns an error code, the BLOB is still closed.

## Open A BLOB For Incremental I/O

>     int sqlite3_blob_open(
>       sqlite3*,
>       const char *zDb,
>       const char *zTable,
>       const char *zColumn,
>       sqlite3_int64 iRow,
>       int flags,
>       sqlite3_blob **ppBlob
>     );

This interfaces opens a handle to the blob located in row iRow,, column zColumn, table zTable in database zDb; in other words, the same blob that would be selected by:

    SELECT zColumn FROM zDb.zTable WHERE rowid = iRow;

If the flags parameter is non-zero, the blob is opened for read and write access. If it is zero, the blob is opened for read access.

On success, SQLITE_OK is returned and the new blob handle is written to *ppBlob. Otherwise an error code is returned and any value written to *ppBlob should not be used by the caller. This function sets the database-handle error code and message accessible via sqlite3_errcode() and sqlite3_errmsg(). (TODO: We should go through and mark all interfaces that behave this way with a similar statement)

## Read Data From A BLOB Incrementally

>     int sqlite3_blob_read(sqlite3_blob *, void *z, int n, int iOffset);

This function is used to read data from an open blob-handle into a caller supplied buffer. n bytes of data are copied into buffer z from the open blob, starting at offset iOffset.

If offset iOffset is less than n bytes from the end of the blob, SQLITE_ERROR is returned and no data is read. If n is less than zero SQLITE_ERROR is returned and no data is read.

On success, SQLITE_OK is returned. Otherwise, an error code or an extended error code is returned.

## Write Data Into A BLOB Incrementally

>     int sqlite3_blob_write(sqlite3_blob *, const void *z, int n, int iOffset);

This function is used to write data into an open blob-handle from a user supplied buffer. n bytes of data are copied from the buffer pointed to by z into the open blob, starting at offset iOffset.

If the blob-handle passed as the first argument was not opened for writing (the flags parameter to sqlite3_blob_open() was zero), this function returns SQLITE_READONLY.

This function may only modify the contents of the blob; it is not possible to increase the size of a blob using this API. If offset iOffset is less than n bytes from the end of the blob, SQLITE_ERROR is returned and no data is written. If n is less than zero SQLITE_ERROR is returned and no data is written.

On success, SQLITE_OK is returned. Otherwise, an error code or an extended error code is returned.

## Register A Callback To Handle SQLITE_BUSY Errors

>     int sqlite3_busy_handler(sqlite3*, int(*)(void*,int), void*);

This routine identifies a callback function that might be invoked whenever an attempt is made to open a database table that another thread or process has locked. If the busy callback is NULL, then SQLITE_BUSY or SQLITE_IOERR_BLOCKED is returned immediately upon encountering the lock. If the busy callback is not NULL, then the callback will be invoked with two arguments. The first argument to the handler is a copy of the void* pointer which is the third argument to this routine. The second argument to the handler is the number of times that the busy handler has been invoked for this locking event. If the busy callback returns 0, then no additional attempts are made to access the database and SQLITE_BUSY or SQLITE_IOERR_BLOCKED is returned. If the callback returns non-zero, then another attempt is made to open the database for reading and the cycle repeats.

The presence of a busy handler does not guarantee that it will be invoked when there is lock contention. If SQLite determines that invoking the busy handler could result in a deadlock, it will go ahead and return SQLITE_BUSY or SQLITE_IOERR_BLOCKED instead of invoking the busy handler. Consider a scenario where one process is holding a read lock that it is trying to promote to a reserved lock and a second process is holding a reserved lock that it is trying to promote to an exclusive lock. The first process cannot proceed because it is blocked by the second and the second process cannot proceed because it is blocked by the first. If both processes invoke the busy handlers, neither will make any progress. Therefore, SQLite returns SQLITE_BUSY for the first process, hoping that this will induce the first process to release its read lock and allow the second process to proceed.

The default busy callback is NULL.

The SQLITE_BUSY error is converted to SQLITE_IOERR_BLOCKED when SQLite is in the middle of a large transaction where all the changes will not fit into the in-memory cache. SQLite will already hold a RESERVED lock on the database file, but it needs to promote this lock to EXCLUSIVE so that it can spill cache pages into the database file without harm to concurrent readers. If it is unable to promote the lock, then the in-memory cache will be left in an inconsistent state and so the error code is promoted from the relatively benign SQLITE_BUSY to the more severe SQLITE_IOERR_BLOCKED. This error code promotion forces an automatic rollback of the changes. See the CorruptionFollowingBusyError wiki page for a discussion of why this is important.

There can only be a single busy handler defined for each database connection. Setting a new busy handler clears any previous one. Note that calling sqlite3_busy_timeout() will also set or clear the busy handler.

### Invariants:

F12311 | The sqlite3_busy_handler() function replaces the busy handler callback in the database connection identified by the 1st parameter with a new busy handler identified by the 2nd and 3rd parameters.
F12312 | The default busy handler for new database connections is NULL.
F12314 | When two or more database connection share a common cache, the busy handler for the database connection currently using the cache is invoked when the cache encounters a lock.
F12316 | If a busy handler callback returns zero, then the SQLite interface that provoked the locking event will return SQLITE_BUSY.
F12318 | SQLite will invokes the busy handler with two argument which are a copy of the pointer supplied by the 3rd parameter to sqlite3_busy_handler() and a count of the number of prior invocations of the busy handler for the same locking event.

### Limitations:

U12319 | A busy handler should not call close the database connection or prepared statement that invoked the busy handler.

## Set A Busy Timeout

>     int sqlite3_busy_timeout(sqlite3*, int ms);

This routine sets a busy handler that sleeps for a while when a table is locked. The handler will sleep multiple times until at least "ms" milliseconds of sleeping have been done. After "ms" milliseconds of sleeping, the handler returns 0 which causes sqlite3_step() to return SQLITE_BUSY or SQLITE_IOERR_BLOCKED.

Calling this routine with an argument less than or equal to zero turns off all busy handlers.

There can only be a single busy handler for a particular database connection. If another busy handler was defined (using sqlite3_busy_handler()) prior to calling this routine, that other busy handler is cleared.

### Invariants:

F12341 | The sqlite3_busy_timeout() function overrides any prior sqlite3_busy_timeout() or sqlite3_busy_handler() setting on the same database connection.
F12343 | If the 2nd parameter to sqlite3_busy_timeout() is less than or equal to zero, then the busy handler is cleared so that all subsequent locking events immediately return SQLITE_BUSY.
F12344 | If the 2nd parameter to sqlite3_busy_timeout() is a positive number N, then a busy handler is set that repeatedly calls the xSleep() method in the VFS interface until either the lock clears or until the cumulative sleep time reported back by xSleep() exceeds N milliseconds.

## Count The Number Of Rows Modified

>     int sqlite3_changes(sqlite3*);

This function returns the number of database rows that were changed or inserted or deleted by the most recently completed SQL statement on the connection specified by the first parameter. Only changes that are directly specified by the INSERT, UPDATE, or DELETE statement are counted. Auxiliary changes caused by triggers are not counted. Use the sqlite3_total_changes() function to find the total number of changes including changes caused by triggers.

A "row changes" is a change to a single row of a single table caused by an INSERT, DELETE, or UPDATE statement. Rows that are changed as side effects of REPLACE constraint resolution, rollback, ABORT processing, DROP TABLE, or by any other mechanisms do not count as direct row changes.

A "trigger context" is a scope of execution that begins and ends with the script of a trigger. Most SQL statements are evaluated outside of any trigger. This is the "top level" trigger context. If a trigger fires from the top level, a new trigger context is entered for the duration of that one trigger. Subtriggers create subcontexts for their duration.

Calling sqlite3_exec() or sqlite3_step() recursively does not create a new trigger context.

This function returns the number of direct row changes in the most recent INSERT, UPDATE, or DELETE statement within the same trigger context.

So when called from the top level, this function returns the number of changes in the most recent INSERT, UPDATE, or DELETE that also occurred at the top level. Within the body of a trigger, the sqlite3_changes() interface can be called to find the number of changes in the most recently completed INSERT, UPDATE, or DELETE statement within the body of the same trigger. However, the number returned does not include in changes caused by subtriggers since they have their own context.

SQLite implements the command "DELETE FROM table" without a WHERE clause by dropping and recreating the table. (This is much faster than going through and deleting individual elements from the table.) Because of this optimization, the deletions in "DELETE FROM table" are not row changes and will not be counted by the sqlite3_changes() or sqlite3_total_changes() functions. To get an accurate count of the number of rows deleted, use "DELETE FROM table WHERE 1" instead.

### Invariants:

F12241 | The sqlite3_changes() function returns the number of row changes caused by the most recent INSERT, UPDATE, or DELETE statement on the same database connection and within the same trigger context, or zero if there have not been any qualifying row changes.

### Limitations:

U12252 | If a separate thread makes changes on the same database connection while sqlite3_changes() is running then the value returned is unpredictable and unmeaningful.

## Reset All Bindings On A Prepared Statement

>     int sqlite3_clear_bindings(sqlite3_stmt*);

Contrary to the intuition of many, sqlite3_reset() does not reset the bindings on a prepared statement. Use this routine to reset all host parameters to NULL.

### Invariants:

F13661 | The sqlite3_clear_bindings(S) interface resets all SQL parameter bindings in prepared statement S back to NULL.

## Closing A Database Connection

>     int sqlite3_close(sqlite3 *);

This routine is the destructor for the sqlite3 object.

Applications should finalize all prepared statements and close all BLOBs associated with the sqlite3 object prior to attempting to close the sqlite3 object.

(TODO: What happens to pending transactions? Are they rolled back, or abandoned?)

### Invariants:

F12011 | The sqlite3_close() interface destroys an sqlite3 object allocated by a prior call to sqlite3_open(), sqlite3_open16(), or sqlite3_open_v2().
F12012 | The sqlite3_close() function releases all memory used by the connection and closes all open files.
F12013 | If the database connection contains prepared statements that have not been finalized by sqlite3_finalize(), then sqlite3_close() returns SQLITE_BUSY and leaves the connection open.
F12014 | Giving sqlite3_close() a NULL pointer is a harmless no-op.

### Limitations:

U12015 | The parameter to sqlite3_close() must be an sqlite3 object pointer previously obtained from sqlite3_open() or the equivalent, or NULL.
U12016 | The parameter to sqlite3_close() must not have been previously closed.

## Number Of Columns In A Result Set

>     int sqlite3_column_count(sqlite3_stmt *pStmt);

Return the number of columns in the result set returned by the prepared statement. This routine returns 0 if pStmt is an SQL statement that does not return data (for example an UPDATE).

### Invariants:

F13711 | The sqlite3_column_count(S) interface returns the number of columns in the result set generated by the prepared statement S, or 0 if S does not generate a result set.

## Number of columns in a result set

>     int sqlite3_data_count(sqlite3_stmt *pStmt);

Return the number of values in the current row of the result set.

### Invariants:

F13771 | After a call to sqlite3_step(S) that returns SQLITE_ROW, the sqlite3_data_count(S) routine will return the same value as the sqlite3_column_count(S) function.
F13772 | After sqlite3_step(S) has returned any value other than SQLITE_ROW or before sqlite3_step(S) has been called on the prepared statement for the first time since it was prepared or reset, the sqlite3_data_count(S) routine returns zero.

## Find The Database Handle Of A Prepared Statement

>     sqlite3 *sqlite3_db_handle(sqlite3_stmt*);

The sqlite3_db_handle interface returns the sqlite3* database handle to which a prepared statement belongs. the database handle returned by sqlite3_db_handle is the same database handle that was the first argument to the sqlite3_prepare_v2() or its variants that was used to create the statement in the first place.

## Enable Or Disable Extension Loading

>     int sqlite3_enable_load_extension(sqlite3 *db, int onoff);

So as not to open security holes in older applications that are unprepared to deal with extension loading, and as a means of disabling extension loading while evaluating user-entered SQL, the following API is provided to turn the sqlite3_load_extension() mechanism on and off. It is off by default. See ticket #1863.

Call the sqlite3_enable_load_extension() routine with onoff==1 to turn extension loading on and call it with onoff==0 to turn it back off again.

## Enable Or Disable Shared Pager Cache

>     int sqlite3_enable_shared_cache(int);

This routine enables or disables the sharing of the database cache and schema data structures between connections to the same database.

Sharing is enabled if the argument is true and disabled if the argument is false.

Cache sharing is enabled and disabled for an entire process. This is a change as of SQLite version 3.5.0. In prior versions of SQLite, sharing was enabled or disabled for each thread separately.

The cache sharing mode set by this interface effects all subsequent calls to sqlite3_open(), sqlite3_open_v2(), and sqlite3_open16(). Existing database connections continue use the sharing mode that was in effect at the time they were opened.

Virtual tables cannot be used with a shared cache. When shared cache is enabled, the sqlite3_create_module() API used to register virtual tables will always return an error.

This routine returns SQLITE_OK if shared cache was enabled or disabled successfully. An error code is returned otherwise.

Shared cache is disabled by default. But this might change in future releases of SQLite. Applications that care about shared cache setting should set it explicitly.

## One-Step Query Execution Interface

>     int sqlite3_exec(
>       sqlite3*,                                  /* An open database */
>       const char *sql,                           /* SQL to be evaluted */
>       int (*callback)(void*,int,char**,char**),  /* Callback function */
>       void *,                                    /* 1st argument to callback */
>       char **errmsg                              /* Error msg written here */
>     );

The sqlite3_exec() interface is a convenient way of running one or more SQL statements without a lot of C code. The SQL statements are passed in as the second parameter to sqlite3_exec(). The statements are evaluated one by one until either an error or an interrupt is encountered or until they are all done. The 3rd parameter is an optional callback that is invoked once for each row of any query results produced by the SQL statements. The 5th parameter tells where to write any error messages.

The sqlite3_exec() interface is implemented in terms of sqlite3_prepare_v2(), sqlite3_step(), and sqlite3_finalize(). The sqlite3_exec() routine does nothing that cannot be done by sqlite3_prepare_v2(), sqlite3_step(), and sqlite3_finalize(). The sqlite3_exec() is just a convenient wrapper.

### Invariants:

F12101 | The sqlite3_exec() interface evaluates zero or more UTF-8 encoded, semicolon-separated, SQL statements in the zero-terminated string of its 2nd parameter within the context of the sqlite3 object given in the 1st parameter.
F12104 | The return value of sqlite3_exec() is SQLITE_OK if all SQL statements run successfully.
F12105 | The return value of sqlite3_exec() is an appropriate non-zero error code if any SQL statement fails.
F12107 | If one or more of the SQL statements handed to sqlite3_exec() return results and the 3rd parameter is not NULL, then the callback function specified by the 3rd parameter is invoked once for each row of result.
F12110 | If the callback returns a non-zero value then sqlite3_exec() will aborted the SQL statement it is currently evaluating, skip all subsequent SQL statements, and return SQLITE_ABORT. (TODO: What happens to *errmsg here? Does the result code for sqlite3_errcode() get set?)
F12113 | The sqlite3_exec() routine will pass its 4th parameter through as the 1st parameter of the callback.
F12116 | The sqlite3_exec() routine sets the 2nd parameter of its callback to be the number of columns in the current row of result.
F12119 | The sqlite3_exec() routine sets the 3rd parameter of its callback to be an array of pointers to strings holding the values for each column in the current result set row as obtained from sqlite3_column_text().
F12122 | The sqlite3_exec() routine sets the 4th parameter of its callback to be an array of pointers to strings holding the names of result columns as obtained from sqlite3_column_name().
F12125 | If the 3rd parameter to sqlite3_exec() is NULL then sqlite3_exec() never invokes a callback. All query results are silently discarded.
F12128 | If an error occurs while parsing or evaluating any of the SQL statements handed to sqlite3_exec() then sqlite3_exec() will return an error code other than SQLITE_OK.
F12131 | If an error occurs while parsing or evaluating any of the SQL handed to sqlite3_exec() and if the 5th parameter (errmsg) to sqlite3_exec() is not NULL, then an error message is allocated using the equivalent of sqlite3_mprintf() and *errmsg is made to point to that message.
F12134 | The sqlite3_exec() routine does not change the value of *errmsg if errmsg is NULL or if there are no errors.
F12137 | The sqlite3_exec() function sets the error code and message accessible via sqlite3_errcode() and sqlite3_errmsg().

### Limitations:

U12141 | The first parameter to sqlite3_exec() must be an valid and open database connection.
U12142 | The database connection must not be closed while sqlite3_exec() is running.
U12143 | The calling function is should use sqlite3_free() to free the memory that *errmsg is left pointing at once the error message is no longer needed.
U12145 | The SQL statement text in the 2nd parameter to sqlite3_exec() must remain unchanged while sqlite3_exec() is running.

## Enable Or Disable Extended Result Codes

>     int sqlite3_extended_result_codes(sqlite3*, int onoff);

The sqlite3_extended_result_codes() routine enables or disables the extended result codes feature of SQLite. The extended result codes are disabled by default for historical compatibility.

### Invariants:

F12201 | Each new database connection has the extended result codes feature disabled by default.
F12202 | The sqlite3_extended_result_codes(D,F) interface will enable extended result codes for the database connection D if the F parameter is true, or disable them if F is false.

## Low-Level Control Of Database Files

>     int sqlite3_file_control(sqlite3*, const char *zDbName, int op, void*);

The sqlite3_file_control() interface makes a direct call to the xFileControl method for the sqlite3_io_methods object associated with a particular database identified by the second argument. The name of the database is the name assigned to the database by the ATTACH SQL command that opened the database. To control the main database file, use the name "main" or a NULL pointer. The third and fourth parameters to this routine are passed directly through to the second and third parameters of the xFileControl method. The return value of the xFileControl method becomes the return value of this routine.

If the second parameter (zDbName) does not match the name of any open database file, then SQLITE_ERROR is returned. This error code is not remembered and will not be recalled by sqlite3_errcode() or sqlite3_errmsg(). The underlying xFileControl method might also return SQLITE_ERROR. There is no way to distinguish between an incorrect zDbName and an SQLITE_ERROR return from the underlying xFileControl method.

See also: SQLITE_FCNTL_LOCKSTATE

## Destroy A Prepared Statement Object

>     int sqlite3_finalize(sqlite3_stmt *pStmt);

The sqlite3_finalize() function is called to delete a prepared statement. If the statement was executed successfully, or not executed at all, then SQLITE_OK is returned. If execution of the statement failed then an error code or extended error code is returned.

This routine can be called at any point during the execution of the prepared statement. If the virtual machine has not completed execution when this routine is called, that is like encountering an error or an interrupt. (See sqlite3_interrupt().) Incomplete updates may be rolled back and transactions cancelled, depending on the circumstances, and the error code returned will be SQLITE_ABORT.

### Invariants:

F11302 | The sqlite3_finalize(S) interface destroys the prepared statement S and releases all memory and file resources held by that object.
F11304 | If the most recent call to sqlite3_step(S) for the prepared statement S returned an error, then sqlite3_finalize(S) returns that same error.

## Test To See If The Database Is In Auto-Commit Mode

>     int sqlite3_get_autocommit(sqlite3*);

The sqlite3_get_autocommit() interfaces returns non-zero or zero if the given database connection is or is not in autocommit mode, respectively. Autocommit mode is on by default. Autocommit mode is disabled by a BEGIN statement. Autocommit mode is reenabled by a COMMIT or ROLLBACK.

If certain kinds of errors occur on a statement within a multi-statement transactions (errors including SQLITE_FULL, SQLITE_IOERR, SQLITE_NOMEM, SQLITE_BUSY, and SQLITE_INTERRUPT) then the transaction might be rolled back automatically. The only way to find out if SQLite automatically rolled back the transaction after an error is to use this function.

### Invariants:

F12931 | The sqlite3_get_autocommit() interface returns non-zero or zero if the given database connection is or is not in autocommit mode, respectively.
F12932 | Autocommit mode is on by default.
F12933 | Autocommit mode is disabled by a successful BEGIN statement.
F12934 | Autocommit mode is enabled by a successful COMMIT or ROLLBACK statement.

### Limitations:

U12936 | If another thread changes the autocommit status of the database connection while this routine is running, then the return value is undefined.

## Interrupt A Long-Running Query

>     void sqlite3_interrupt(sqlite3*);

This function causes any pending database operation to abort and return at its earliest opportunity. This routine is typically called in response to a user action such as pressing "Cancel" or Ctrl-C where the user wants a long query operation to halt immediately.

It is safe to call this routine from a thread different from the thread that is currently running the database operation. But it is not safe to call this routine with a database connection that is closed or might close before sqlite3_interrupt() returns.

If an SQL is very nearly finished at the time when sqlite3_interrupt() is called, then it might not have an opportunity to be interrupted. It might continue to completion. An SQL operation that is interrupted will return SQLITE_INTERRUPT. If the interrupted SQL operation is an INSERT, UPDATE, or DELETE that is inside an explicit transaction, then the entire transaction will be rolled back automatically. A call to sqlite3_interrupt() has no effect on SQL statements that are started after sqlite3_interrupt() returns.

### Invariants:

F12271 | The sqlite3_interrupt() interface will force all running SQL statements associated with the same database connection to halt after processing at most one additional row of data.
F12272 | Any SQL statement that is interrupted by sqlite3_interrupt() will return SQLITE_INTERRUPT.

### Limitations:

U12279 | If the database connection closes while sqlite3_interrupt() is running then bad things will likely happen.

## Last Insert Rowid

>     sqlite3_int64 sqlite3_last_insert_rowid(sqlite3*);

Each entry in an SQLite table has a unique 64-bit signed integer key called the "rowid". The rowid is always available as an undeclared column named ROWID, OID, or _ROWID_ as long as those names are not also used by explicitly declared columns. If the table has a column of type INTEGER PRIMARY KEY then that column is another an alias for the rowid.

This routine returns the rowid of the most recent successful INSERT into the database from the database connection shown in the first argument. If no successful inserts have ever occurred on this database connection, zero is returned.

If an INSERT occurs within a trigger, then the rowid of the inserted row is returned by this routine as long as the trigger is running. But once the trigger terminates, the value returned by this routine reverts to the last value inserted before the trigger fired.

An INSERT that fails due to a constraint violation is not a successful insert and does not change the value returned by this routine. Thus INSERT OR FAIL, INSERT OR IGNORE, INSERT OR ROLLBACK, and INSERT OR ABORT make no changes to the return value of this routine when their insertion fails. When INSERT OR REPLACE encounters a constraint violation, it does not fail. The INSERT continues to completion after deleting rows that caused the constraint problem so INSERT OR REPLACE will always change the return value of this interface.

For the purposes of this routine, an insert is considered to be successful even if it is subsequently rolled back.

### Invariants:

F12221 | The sqlite3_last_insert_rowid() function returns the rowid of the most recent successful insert done on the same database connection and within the same trigger context, or zero if there have been no qualifying inserts on that connection.
F12223 | The sqlite3_last_insert_rowid() function returns same value when called from the same trigger context immediately before and after a ROLLBACK.

### Limitations:

U12232 | If separate thread does a new insert on the same database connection while the sqlite3_last_insert_rowid() function is running and thus changes the last insert rowid, then the value returned by sqlite3_last_insert_rowid() is unpredictable and might not equal either the old or the new last insert rowid.

## Load An Extension

>     int sqlite3_load_extension(
>       sqlite3 *db,          /* Load the extension into this database connection */
>       const char *zFile,    /* Name of the shared library containing extension */
>       const char *zProc,    /* Entry point.  Derived from zFile if 0 */
>       char **pzErrMsg       /* Put error message here if not 0 */
>     );

The sqlite3_load_extension() interface attempts to load an SQLite extension library contained in the file zFile. The entry point is zProc. zProc may be 0 in which case the name of the entry point defaults to "sqlite3_extension_init".

The sqlite3_load_extension() interface shall return SQLITE_OK on success and SQLITE_ERROR if something goes wrong.

If an error occurs and pzErrMsg is not 0, then the sqlite3_load_extension() interface shall attempt to fill *pzErrMsg with error message text stored in memory obtained from sqlite3_malloc(). The calling function should free this memory by calling sqlite3_free().

Extension loading must be enabled using sqlite3_enable_load_extension() prior to calling this API or an error will be returned.

## Query Progress Callbacks

>     void sqlite3_progress_handler(sqlite3*, int, int(*)(void*), void*);

This routine configures a callback function - the progress callback - that is invoked periodically during long running calls to sqlite3_exec(), sqlite3_step() and sqlite3_get_table(). An example use for this interface is to keep a GUI updated during a large query.

If the progress callback returns non-zero, the opertion is interrupted. This feature can be used to implement a "Cancel" button on a GUI dialog box.

### Invariants:

F12911 | The callback function registered by sqlite3_progress_handler() is invoked periodically during long running calls to sqlite3_step().
F12912 | The progress callback is invoked once for every N virtual machine opcodes, where N is the second argument to the sqlite3_progress_handler() call that registered the callback. (TODO: What if N is less than 1?)
F12913 | The progress callback itself is identified by the third argument to sqlite3_progress_handler().
F12914 | The fourth argument sqlite3_progress_handler() is a void pointer passed to the progress callback function each time it is invoked.
F12915 | If a call to sqlite3_step() results in fewer than N opcodes being executed, then the progress callback is never invoked.
F12916 | Every call to sqlite3_progress_handler() overwrites any previously registere progress handler.
F12917 | If the progress handler callback is NULL then no progress handler is invoked.
F12918 | If the progress callback returns a result other than 0, then the behavior is a if sqlite3_interrupt() had been called.

## Attempt To Free Heap Memory

>     int sqlite3_release_memory(int);

The sqlite3_release_memory() interface attempts to free N bytes of heap memory by deallocating non-essential memory allocations held by the database labrary. Memory used to cache database pages to improve performance is an example of non-essential memory. sqlite3_release_memory() returns the number of bytes actually freed, which might be more or less than the amount requested.

## Reset A Prepared Statement Object

>     int sqlite3_reset(sqlite3_stmt *pStmt);

The sqlite3_reset() function is called to reset a prepared statement object. back to its initial state, ready to be re-executed. Any SQL statement variables that had values bound to them using the sqlite3_bind_*() API retain their values. Use sqlite3_clear_bindings() to reset the bindings.

The sqlite3_reset(S) interface resets the prepared statement S back to the beginning of its program.

If the most recent call to sqlite3_step(S) for prepared statement S returned SQLITE_ROW or SQLITE_DONE, or if sqlite3_step(S) has never before been called on S, then sqlite3_reset(S) returns SQLITE_OK.

If the most recent call to sqlite3_step(S) for prepared statement S indicated an error, then sqlite3_reset(S) returns an appropriate error code.

The sqlite3_reset(S) interface does not change the values of any bindings on prepared statement S.

## Reset Automatic Extension Loading

>     void sqlite3_reset_auto_extension(void);

This function disables all previously registered automatic extensions. This routine undoes the effect of all prior sqlite3_auto_extension() calls.

This call disabled automatic extensions in all threads.

This interface is experimental and is subject to change or removal in future releases of SQLite.

## Compile-Time Authorization Callbacks

>     int sqlite3_set_authorizer(
>       sqlite3*,
>       int (*xAuth)(void*,int,const char*,const char*,const char*,const char*),
>       void *pUserData
>     );

This routine registers a authorizer callback with a particular database connection, supplied in the first argument. The authorizer callback is invoked as SQL statements are being compiled by sqlite3_prepare() or its variants sqlite3_prepare_v2(), sqlite3_prepare16() and sqlite3_prepare16_v2(). At various points during the compilation process, as logic is being created to perform various actions, the authorizer callback is invoked to see if those actions are allowed. The authorizer callback should return SQLITE_OK to allow the action, SQLITE_IGNORE to disallow the specific action but allow the SQL statement to continue to be compiled, or SQLITE_DENY to cause the entire SQL statement to be rejected with an error. If the authorizer callback returns any value other than SQLITE_IGNORE, SQLITE_OK, or SQLITE_DENY then sqlite3_prepare_v2() or equivalent call that triggered the authorizer will fail with an error message.

When the callback returns SQLITE_OK, that means the operation requested is ok. When the callback returns SQLITE_DENY, the sqlite3_prepare_v2() or equivalent call that triggered the authorizer will fail with an error message explaining that access is denied. If the authorizer code is SQLITE_READ and the callback returns SQLITE_IGNORE then the prepared statement is constructed to insert a NULL value in place of the table column that would have been read if SQLITE_OK had been returned. The SQLITE_IGNORE return can be used to deny an untrusted user access to individual columns of a table.

The first parameter to the authorizer callback is a copy of the third parameter to the sqlite3_set_authorizer() interface. The second parameter to the callback is an integer action code that specifies the particular action to be authorized. The third through sixth parameters to the callback are zero-terminated strings that contain additional details about the action to be authorized.

An authorizer is used when preparing SQL statements from an untrusted source, to ensure that the SQL statements do not try to access data that they are not allowed to see, or that they do not try to execute malicious statements that damage the database. For example, an application may allow a user to enter arbitrary SQL queries for evaluation by a database. But the application does not want the user to be able to make arbitrary changes to the database. An authorizer could then be put in place while the user-entered SQL is being prepared that disallows everything except SELECT statements.

Only a single authorizer can be in place on a database connection at a time. Each call to sqlite3_set_authorizer overrides the previous call. Disable the authorizer by installing a NULL callback. The authorizer is disabled by default.

Note that the authorizer callback is invoked only during sqlite3_prepare() or its variants. Authorization is not performed during statement evaluation in sqlite3_step().

### Invariants:

F12501 | The sqlite3_set_authorizer(D,...) interface registers a authorizer callback with database connection D.
F12502 | The authorizer callback is invoked as SQL statements are being compiled
F12503 | If the authorizer callback returns any value other than SQLITE_IGNORE, SQLITE_OK, or SQLITE_DENY then the sqlite3_prepare_v2() or equivalent call that caused the authorizer callback to run shall fail with an SQLITE_ERROR error code and an appropriate error message.
F12504 | When the authorizer callback returns SQLITE_OK, the operation described is coded normally.
F12505 | When the authorizer callback returns SQLITE_DENY, the sqlite3_prepare_v2() or equivalent call that caused the authorizer callback to run shall fail with an SQLITE_ERROR error code and an error message explaining that access is denied.
F12506 | If the authorizer code (the 2nd parameter to the authorizer callback) is SQLITE_READ and the authorizer callback returns SQLITE_IGNORE then the prepared statement is constructed to insert a NULL value in place of the table column that would have been read if SQLITE_OK had been returned.
F12507 | If the authorizer code (the 2nd parameter to the authorizer callback) is anything other than SQLITE_READ, then a return of SQLITE_IGNORE has the same effect as SQLITE_DENY.
F12510 | The first parameter to the authorizer callback is a copy of the third parameter to the sqlite3_set_authorizer() interface.
F12511 | The second parameter to the callback is an integer action code that specifies the particular action to be authorized.
F12512 | The third through sixth parameters to the callback are zero-terminated strings that contain additional details about the action to be authorized.
F12520 | Each call to sqlite3_set_authorizer() overrides the any previously installed authorizer.
F12521 | A NULL authorizer means that no authorization callback is invoked.
F12522 | The default authorizer is NULL.

## Suspend Execution For A Short Time

>     int sqlite3_sleep(int);

The sqlite3_sleep() function causes the current thread to suspend execution for at least a number of milliseconds specified in its parameter.

If the operating system does not support sleep requests with millisecond time resolution, then the time will be rounded up to the nearest second. The number of milliseconds of sleep actually requested from the operating system is returned.

SQLite implements this interface by calling the xSleep() method of the default sqlite3_vfs object.

## Impose A Limit On Heap Size

>     void sqlite3_soft_heap_limit(int);

The sqlite3_soft_heap_limit() interface places a "soft" limit on the amount of heap memory that may be allocated by SQLite. If an internal allocation is requested that would exceed the soft heap limit, sqlite3_release_memory() is invoked one or more times to free up some space before the allocation is made.

The limit is called "soft", because if sqlite3_release_memory() cannot free sufficient memory to prevent the limit from being exceeded, the memory is allocated anyway and the current operation proceeds.

A negative or zero value for N means that there is no soft heap limit and sqlite3_release_memory() will only be called when memory is exhausted. The default value for the soft heap limit is zero.

SQLite makes a best effort to honor the soft heap limit. But if the soft heap limit cannot honored, execution will continue without error or notification. This is why the limit is called a "soft" limit. It is advisory only.

Prior to SQLite version 3.5.0, this routine only constrained the memory allocated by a single thread - the same thread in which this routine runs. Beginning with SQLite version 3.5.0, the soft heap limit is applied to all threads. The value specified for the soft heap limit is an upper bound on the total memory allocation for all threads. In version 3.5.0 there is no mechanism for limiting the heap usage for individual threads.

## Evaluate An SQL Statement

>     int sqlite3_step(sqlite3_stmt*);

After an prepared statement has been prepared with a call to either sqlite3_prepare_v2() or sqlite3_prepare16_v2() or to one of the legacy interfaces sqlite3_prepare() or sqlite3_prepare16(), then this function must be called one or more times to evaluate the statement.

The details of the behavior of this sqlite3_step() interface depend on whether the statement was prepared using the newer "v2" interface sqlite3_prepare_v2() and sqlite3_prepare16_v2() or the older legacy interface sqlite3_prepare() and sqlite3_prepare16(). The use of the new "v2" interface is recommended for new applications but the legacy interface will continue to be supported.

In the lagacy interface, the return value will be either SQLITE_BUSY, SQLITE_DONE, SQLITE_ROW, SQLITE_ERROR, or SQLITE_MISUSE. With the "v2" interface, any of the other result code or extended result code might be returned as well.

SQLITE_BUSY means that the database engine was unable to acquire the database locks it needs to do its job. If the statement is a COMMIT or occurs outside of an explicit transaction, then you can retry the statement. If the statement is not a COMMIT and occurs within a explicit transaction then you should rollback the transaction before continuing.

SQLITE_DONE means that the statement has finished executing successfully. sqlite3_step() should not be called again on this virtual machine without first calling sqlite3_reset() to reset the virtual machine back to its initial state.

If the SQL statement being executed returns any data, then SQLITE_ROW is returned each time a new row of data is ready for processing by the caller. The values may be accessed using the column access functions. sqlite3_step() is called again to retrieve the next row of data.

SQLITE_ERROR means that a run-time error (such as a constraint violation) has occurred. sqlite3_step() should not be called again on the VM. More information may be found by calling sqlite3_errmsg(). With the legacy interface, a more specific error code (example: SQLITE_INTERRUPT, SQLITE_SCHEMA, SQLITE_CORRUPT, and so forth) can be obtained by calling sqlite3_reset() on the prepared statement. In the "v2" interface, the more specific error code is returned directly by sqlite3_step().

SQLITE_MISUSE means that the this routine was called inappropriately. Perhaps it was called on a prepared statement that has already been finalized or on one that had previously returned SQLITE_ERROR or SQLITE_DONE. Or it could be the case that the same database connection is being used by two or more threads at the same moment in time.

Goofy Interface Alert: In the legacy interface, the sqlite3_step() API always returns a generic error code, SQLITE_ERROR, following any error other than SQLITE_BUSY and SQLITE_MISUSE. You must call sqlite3_reset() or sqlite3_finalize() in order to find one of the specific error codes that better describes the error. We admit that this is a goofy design. The problem has been fixed with the "v2" interface. If you prepare all of your SQL statements using either sqlite3_prepare_v2() or sqlite3_prepare16_v2() instead of the legacy sqlite3_prepare() and sqlite3_prepare16(), then the more specific error codes are returned directly by sqlite3_step(). The use of the "v2" interface is recommended.

### Invariants:

F13202 | If prepared statement S is ready to be run, then sqlite3_step(S) advances that prepared statement until to completion or until it is ready to return another row of the result set or an interrupt or run-time error occurs.
F15304 | When a call to sqlite3_step(S) causes the prepared statement S to run to completion, the function returns SQLITE_DONE.
F15306 | When a call to sqlite3_step(S) stops because it is ready to return another row of the result set, it returns SQLITE_ROW.
F15308 | If a call to sqlite3_step(S) encounters an interrupt or a run-time error, it returns an appropraite error code that is not one of SQLITE_OK, SQLITE_ROW, or SQLITE_DONE.
F15310 | If an interrupt or run-time error occurs during a call to sqlite3_step(S) for a prepared statement S created using legacy interfaces sqlite3_prepare() or sqlite3_prepare16() then the function returns either SQLITE_ERROR, SQLITE_BUSY, or SQLITE_MISUSE.

## Extract Metadata About A Column Of A Table

>     int sqlite3_table_column_metadata(
>       sqlite3 *db,                /* Connection handle */
>       const char *zDbName,        /* Database name or NULL */
>       const char *zTableName,     /* Table name */
>       const char *zColumnName,    /* Column name */
>       char const **pzDataType,    /* OUTPUT: Declared data type */
>       char const **pzCollSeq,     /* OUTPUT: Collation sequence name */
>       int *pNotNull,              /* OUTPUT: True if NOT NULL constraint exists */
>       int *pPrimaryKey,           /* OUTPUT: True if column part of PK */
>       int *pAutoinc               /* OUTPUT: True if column is auto-increment */
>     );

This routine returns meta-data about a specific column of a specific database table accessible using the connection handle passed as the first function argument.

The column is identified by the second, third and fourth parameters to this function. The second parameter is either the name of the database (i.e. "main", "temp" or an attached database) containing the specified table or NULL. If it is NULL, then all attached databases are searched for the table using the same algorithm as the database engine uses to resolve unqualified table references.

The third and fourth parameters to this function are the table and column name of the desired column, respectively. Neither of these parameters may be NULL.

Meta information is returned by writing to the memory locations passed as the 5th and subsequent parameters to this function. Any of these arguments may be NULL, in which case the corresponding element of meta information is ommitted.

    Parameter     Output Type      Description
    -----------------------------------

    5th         const char*      Data type
    6th         const char*      Name of the default collation sequence
    7th         int              True if the column has a NOT NULL constraint
    8th         int              True if the column is part of the PRIMARY KEY
    9th         int              True if the column is AUTOINCREMENT

The memory pointed to by the character pointers returned for the declaration type and collation sequence is valid only until the next call to any sqlite API function.

If the specified table is actually a view, then an error is returned.

If the specified column is "rowid", "oid" or "_rowid_" and an INTEGER PRIMARY KEY column has been explicitly declared, then the output parameters are set for the explicitly declared column. If there is no explicitly declared IPK column, then the output parameters are set as follows:

    data type: "INTEGER"
    collation sequence: "BINARY"
    not null: 0
    primary key: 1
    auto increment: 0

This function may load one or more schemas from database files. If an error occurs during this process, or if the requested table or column cannot be found, an SQLITE error code is returned and an error message left in the database handle (to be retrieved using sqlite3_errmsg()).

This API is only available if the library was compiled with the SQLITE_ENABLE_COLUMN_METADATA preprocessor symbol defined.

## Testing Interface

>     int sqlite3_test_control(int op, ...);

The sqlite3_test_control() interface is used to read out internal state of SQLite and to inject faults into SQLite for testing purposes. The first parameter a operation code that determines the number, meaning, and operation of all subsequent parameters.

This interface is not for use by applications. It exists solely for verifying the correct operation of the SQLite library. Depending on how the SQLite library is compiled, this interface might not exist.

The details of the operation codes, their meanings, the parameters they take, and what they do are all subject to change without notice. Unlike most of the SQLite API, this function is not guaranteed to operate consistently from one release to the next.

## Test To See If The Library Is Threadsafe

>     int sqlite3_threadsafe(void);

SQLite can be compiled with or without mutexes. When the SQLITE_THREADSAFE C preprocessor macro is true, mutexes are enabled and SQLite is threadsafe. When that macro os false, the mutexes are omitted. Without the mutexes, it is not safe to use SQLite from more than one thread.

There is a measurable performance penalty for enabling mutexes. So if speed is of utmost importance, it makes sense to disable the mutexes. But for maximum safety, mutexes should be enabled. The default behavior is for mutexes to be enabled.

This interface can be used by a program to make sure that the version of SQLite that it is linking against was compiled with the desired setting of the SQLITE_THREADSAFE macro.

### Invariants:

F10101 | The sqlite3_threadsafe() function returns nonzero if SQLite was compiled with its mutexes enabled or zero if SQLite was compiled with mutexes disabled.

## Total Number Of Rows Modified

>     int sqlite3_total_changes(sqlite3*);

This function returns the number of row changes caused by INSERT, UPDATE or DELETE statements since the database handle was opened. The count includes all changes from all trigger contexts. But the count does not include changes used to implement REPLACE constraints, do rollbacks or ABORT processing, or DROP table processing. The changes are counted as soon as the statement that makes them is completed (when the statement handle is passed to sqlite3_reset() or sqlite3_finalize()).

SQLite implements the command "DELETE FROM table" without a WHERE clause by dropping and recreating the table. (This is much faster than going through and deleting individual elements form the table.) Because of this optimization, the change count for "DELETE FROM table" will be zero regardless of the number of elements that were originally in the table. To get an accurate count of the number of rows deleted, use "DELETE FROM table WHERE 1" instead.

See also the sqlite3_changes() interface.

### Invariants:

F12261 | The sqlite3_total_changes() returns the total number of row changes caused by INSERT, UPDATE, and/or DELETE statements on the same database connection, in any trigger context, since the database connection was created.

### Limitations:

U12264 | If a separate thread makes changes on the same database connection while sqlite3_total_changes() is running then the value returned is unpredictable and unmeaningful.

## Data Change Notification Callbacks

>     void *sqlite3_update_hook(
>       sqlite3*,
>       void(*)(void *,int ,char const *,char const *,sqlite3_int64),
>       void*
>     );

The sqlite3_update_hook() interface registers a callback function with the database connection identified by the first argument to be invoked whenever a row is updated, inserted or deleted. Any callback set by a previous call to this function for the same database connection is overridden.

The second argument is a pointer to the function to invoke when a row is updated, inserted or deleted. The first argument to the callback is a copy of the third argument to sqlite3_update_hook(). The second callback argument is one of SQLITE_INSERT, SQLITE_DELETE or SQLITE_UPDATE, depending on the operation that caused the callback to be invoked. The third and fourth arguments to the callback contain pointers to the database and table name containing the affected row. The final callback parameter is the rowid of the row. In the case of an update, this is the rowid after the update takes place.

The update hook is not invoked when internal system tables are modified (i.e. sqlite_master and sqlite_sequence).

If another function was previously registered, its pArg value is returned. Otherwise NULL is returned.

## User Data For Functions

>     void *sqlite3_user_data(sqlite3_context*);

The sqlite3_user_data() interface returns a copy of the pointer that was the pUserData parameter (the 5th parameter) of the the sqlite3_create_function() and sqlite3_create_function16() routines that originally registered the application defined function.

This routine must be called from the same thread in which the application-defined function is running.

## Result Codes

>     #define SQLITE_OK           0   /* Successful result */
>     /* beginning-of-error-codes */
>     #define SQLITE_ERROR        1   /* SQL error or missing database */
>     #define SQLITE_INTERNAL     2   /* Internal logic error in SQLite */
>     #define SQLITE_PERM         3   /* Access permission denied */
>     #define SQLITE_ABORT        4   /* Callback routine requested an abort */
>     #define SQLITE_BUSY         5   /* The database file is locked */
>     #define SQLITE_LOCKED       6   /* A table in the database is locked */
>     #define SQLITE_NOMEM        7   /* A malloc() failed */
>     #define SQLITE_READONLY     8   /* Attempt to write a readonly database */
>     #define SQLITE_INTERRUPT    9   /* Operation terminated by sqlite3_interrupt()*/
>     #define SQLITE_IOERR       10   /* Some kind of disk I/O error occurred */
>     #define SQLITE_CORRUPT     11   /* The database disk image is malformed */
>     #define SQLITE_NOTFOUND    12   /* NOT USED. Table or record not found */
>     #define SQLITE_FULL        13   /* Insertion failed because database is full */
>     #define SQLITE_CANTOPEN    14   /* Unable to open the database file */
>     #define SQLITE_PROTOCOL    15   /* NOT USED. Database lock protocol error */
>     #define SQLITE_EMPTY       16   /* Database is empty */
>     #define SQLITE_SCHEMA      17   /* The database schema changed */
>     #define SQLITE_TOOBIG      18   /* String or BLOB exceeds size limit */
>     #define SQLITE_CONSTRAINT  19   /* Abort due to constraint violation */
>     #define SQLITE_MISMATCH    20   /* Data type mismatch */
>     #define SQLITE_MISUSE      21   /* Library used incorrectly */
>     #define SQLITE_NOLFS       22   /* Uses OS features not supported on host */
>     #define SQLITE_AUTH        23   /* Authorization denied */
>     #define SQLITE_FORMAT      24   /* Auxiliary database format error */
>     #define SQLITE_RANGE       25   /* 2nd parameter to sqlite3_bind out of range */
>     #define SQLITE_NOTADB      26   /* File opened that is not a database file */
>     #define SQLITE_ROW         100  /* sqlite3_step() has another row ready */
>     #define SQLITE_DONE        101  /* sqlite3_step() has finished executing */
>     /* end-of-error-codes */

Many SQLite functions return an integer result code from the set shown here in order to indicates success or failure.

See also: extended result codes

## Flags for the xAccess VFS method

>     #define SQLITE_ACCESS_EXISTS    0
>     #define SQLITE_ACCESS_READWRITE 1
>     #define SQLITE_ACCESS_READ      2

These integer constants can be used as the third parameter to the xAccess method of an sqlite3_vfs object. They determine the kind of what kind of permissions the xAccess method is looking for. With SQLITE_ACCESS_EXISTS, the xAccess method simply checks to see if the file exists. With SQLITE_ACCESS_READWRITE, the xAccess method checks to see if the file is both readable and writable. With SQLITE_ACCESS_READ the xAccess method checks to see if the file is readable.

## Authorizer Action Codes

>     /******************************************* 3rd ************ 4th ***********/
>     #define SQLITE_CREATE_INDEX          1   /* Index Name      Table Name      */
>     #define SQLITE_CREATE_TABLE          2   /* Table Name      NULL            */
>     #define SQLITE_CREATE_TEMP_INDEX     3   /* Index Name      Table Name      */
>     #define SQLITE_CREATE_TEMP_TABLE     4   /* Table Name      NULL            */
>     #define SQLITE_CREATE_TEMP_TRIGGER   5   /* Trigger Name    Table Name      */
>     #define SQLITE_CREATE_TEMP_VIEW      6   /* View Name       NULL            */
>     #define SQLITE_CREATE_TRIGGER        7   /* Trigger Name    Table Name      */
>     #define SQLITE_CREATE_VIEW           8   /* View Name       NULL            */
>     #define SQLITE_DELETE                9   /* Table Name      NULL            */
>     #define SQLITE_DROP_INDEX           10   /* Index Name      Table Name      */
>     #define SQLITE_DROP_TABLE           11   /* Table Name      NULL            */
>     #define SQLITE_DROP_TEMP_INDEX      12   /* Index Name      Table Name      */
>     #define SQLITE_DROP_TEMP_TABLE      13   /* Table Name      NULL            */
>     #define SQLITE_DROP_TEMP_TRIGGER    14   /* Trigger Name    Table Name      */
>     #define SQLITE_DROP_TEMP_VIEW       15   /* View Name       NULL            */
>     #define SQLITE_DROP_TRIGGER         16   /* Trigger Name    Table Name      */
>     #define SQLITE_DROP_VIEW            17   /* View Name       NULL            */
>     #define SQLITE_INSERT               18   /* Table Name      NULL            */
>     #define SQLITE_PRAGMA               19   /* Pragma Name     1st arg or NULL */
>     #define SQLITE_READ                 20   /* Table Name      Column Name     */
>     #define SQLITE_SELECT               21   /* NULL            NULL            */
>     #define SQLITE_TRANSACTION          22   /* NULL            NULL            */
>     #define SQLITE_UPDATE               23   /* Table Name      Column Name     */
>     #define SQLITE_ATTACH               24   /* Filename        NULL            */
>     #define SQLITE_DETACH               25   /* Database Name   NULL            */
>     #define SQLITE_ALTER_TABLE          26   /* Database Name   Table Name      */
>     #define SQLITE_REINDEX              27   /* Index Name      NULL            */
>     #define SQLITE_ANALYZE              28   /* Table Name      NULL            */
>     #define SQLITE_CREATE_VTABLE        29   /* Table Name      Module Name     */
>     #define SQLITE_DROP_VTABLE          30   /* Table Name      Module Name     */
>     #define SQLITE_FUNCTION             31   /* Function Name   NULL            */
>     #define SQLITE_COPY                  0   /* No longer used */

The sqlite3_set_authorizer() interface registers a callback function that is invoked to authorizer certain SQL statement actions. The second parameter to the callback is an integer code that specifies what action is being authorized. These are the integer action codes that the authorizer callback may be passed.

These action code values signify what kind of operation is to be authorized. The 3rd and 4th parameters to the authorization callback function will be parameters or NULL depending on which of these codes is used as the second parameter. The 5th parameter to the authorizer callback is the name of the database ("main", "temp", etc.) if applicable. The 6th parameter to the authorizer callback is the name of the inner-most trigger or view that is responsible for the access attempt or NULL if this access attempt is directly from top-level SQL code.

### Invariants:

F12551 | The second parameter to an authorizer callback is always an integer [SQLITE_COPY that specifies what action is being authorized.
F12552 | The 3rd and 4th parameters to the authorization callback function will be parameters or NULL depending on which authorizer code is used as the second parameter.
F12553 | The 5th parameter to the authorizer callback is the name of the database (example: "main", "temp", etc.) if applicable.
F12554 | The 6th parameter to the authorizer callback is the name of the inner-most trigger or view that is responsible for the access attempt or NULL if this access attempt is directly from top-level SQL code.

## Text Encodings

>     #define SQLITE_UTF8           1
>     #define SQLITE_UTF16LE        2
>     #define SQLITE_UTF16BE        3
>     #define SQLITE_UTF16          4    /* Use native byte order */
>     #define SQLITE_ANY            5    /* sqlite3_create_function only */
>     #define SQLITE_UTF16_ALIGNED  8    /* sqlite3_create_collation only */

These constant define integer codes that represent the various text encodings supported by SQLite.

## Fundamental Datatypes

>     #define SQLITE_INTEGER  1
>     #define SQLITE_FLOAT    2
>     #define SQLITE_BLOB     4
>     #define SQLITE_NULL     5
>     #ifdef SQLITE_TEXT
>     # undef SQLITE_TEXT
>     #else
>     # define SQLITE_TEXT     3
>     #endif
>     #define SQLITE3_TEXT     3

Every value in SQLite has one of five fundamental datatypes:

- 64-bit signed integer
- 64-bit IEEE floating point number
- string
- BLOB
- NULL

These constants are codes for each of those types.

Note that the SQLITE_TEXT constant was also used in SQLite version 2 for a completely different meaning. Software that links against both SQLite version 2 and SQLite version 3 should use SQLITE3_TEXT not SQLITE_TEXT.

## Authorizer Return Codes

>     #define SQLITE_DENY   1   /* Abort the SQL statement with an error */
>     #define SQLITE_IGNORE 2   /* Don't allow access, but don't generate an error */

The authorizer callback function must return either SQLITE_OK or one of these two constants in order to signal SQLite whether or not the action is permitted. See the authorizer documentation for additional information.

## Device Characteristics

>     #define SQLITE_IOCAP_ATOMIC          0x00000001
>     #define SQLITE_IOCAP_ATOMIC512       0x00000002
>     #define SQLITE_IOCAP_ATOMIC1K        0x00000004
>     #define SQLITE_IOCAP_ATOMIC2K        0x00000008
>     #define SQLITE_IOCAP_ATOMIC4K        0x00000010
>     #define SQLITE_IOCAP_ATOMIC8K        0x00000020
>     #define SQLITE_IOCAP_ATOMIC16K       0x00000040
>     #define SQLITE_IOCAP_ATOMIC32K       0x00000080
>     #define SQLITE_IOCAP_ATOMIC64K       0x00000100
>     #define SQLITE_IOCAP_SAFE_APPEND     0x00000200
>     #define SQLITE_IOCAP_SEQUENTIAL      0x00000400

The xDeviceCapabilities method of the sqlite3_io_methods object returns an integer which is a vector of the these bit values expressing I/O characteristics of the mass storage device that holds the file that the sqlite3_io_methods refers to.

The SQLITE_IOCAP_ATOMIC property means that all writes of any size are atomic. The SQLITE_IOCAP_ATOMICnnn values mean that writes of blocks that are nnn bytes in size and are aligned to an address which is an integer multiple of nnn are atomic. The SQLITE_IOCAP_SAFE_APPEND value means that when data is appended to a file, the data is appended first then the size of the file is extended, never the other way around. The SQLITE_IOCAP_SEQUENTIAL property means that information is written to disk in the same order as calls to xWrite().

## Extended Result Codes

>     #define SQLITE_IOERR_READ          (SQLITE_IOERR | (1<<8))
>     #define SQLITE_IOERR_SHORT_READ    (SQLITE_IOERR | (2<<8))
>     #define SQLITE_IOERR_WRITE         (SQLITE_IOERR | (3<<8))
>     #define SQLITE_IOERR_FSYNC         (SQLITE_IOERR | (4<<8))
>     #define SQLITE_IOERR_DIR_FSYNC     (SQLITE_IOERR | (5<<8))
>     #define SQLITE_IOERR_TRUNCATE      (SQLITE_IOERR | (6<<8))
>     #define SQLITE_IOERR_FSTAT         (SQLITE_IOERR | (7<<8))
>     #define SQLITE_IOERR_UNLOCK        (SQLITE_IOERR | (8<<8))
>     #define SQLITE_IOERR_RDLOCK        (SQLITE_IOERR | (9<<8))
>     #define SQLITE_IOERR_DELETE        (SQLITE_IOERR | (10<<8))
>     #define SQLITE_IOERR_BLOCKED       (SQLITE_IOERR | (11<<8))
>     #define SQLITE_IOERR_NOMEM         (SQLITE_IOERR | (12<<8))

In its default configuration, SQLite API routines return one of 26 integer result codes. However, experience has shown that many of these result codes are too course-grained. They do not provide as much information about problems as programmers might like. In an effort to address this, newer versions of SQLite (version 3.3.8 and later) include support for additional result codes that provide more detailed information about errors. The extended result codes are enabled or disabled for each database connection using the sqlite3_extended_result_codes() API.

Some of the available extended result codes are listed here. One may expect the number of extended result codes will be expand over time. Software that uses extended result codes should expect to see new result codes in future releases of SQLite.

The SQLITE_OK result code will never be extended. It will always be exactly zero.

### Invariants:

F10223 | The symbolic name for an extended result code always contains a related primary result code as a prefix.
F10224 | Primary result code names contain a single "_" character.
F10225 | Extended result code names contain two or more "_" characters.
F10226 | The numeric value of an extended result code contains the numeric value of its corresponding primary result code it its least significant 8 bits.

## File Locking Levels

>     #define SQLITE_LOCK_NONE          0
>     #define SQLITE_LOCK_SHARED        1
>     #define SQLITE_LOCK_RESERVED      2
>     #define SQLITE_LOCK_PENDING       3
>     #define SQLITE_LOCK_EXCLUSIVE     4

SQLite uses one of these integer values as the second argument to calls it makes to the xLock() and xUnlock() methods of an sqlite3_io_methods object.

## Mutex Types

>     #define SQLITE_MUTEX_FAST             0
>     #define SQLITE_MUTEX_RECURSIVE        1
>     #define SQLITE_MUTEX_STATIC_MASTER    2
>     #define SQLITE_MUTEX_STATIC_MEM       3  /* sqlite3_malloc() */
>     #define SQLITE_MUTEX_STATIC_MEM2      4  /* sqlite3_release_memory() */
>     #define SQLITE_MUTEX_STATIC_PRNG      5  /* sqlite3_random() */
>     #define SQLITE_MUTEX_STATIC_LRU       6  /* lru page list */

The sqlite3_mutex_alloc() interface takes a single argument which is one of these integer constants.

## Flags For File Open Operations

>     #define SQLITE_OPEN_READONLY         0x00000001
>     #define SQLITE_OPEN_READWRITE        0x00000002
>     #define SQLITE_OPEN_CREATE           0x00000004
>     #define SQLITE_OPEN_DELETEONCLOSE    0x00000008
>     #define SQLITE_OPEN_EXCLUSIVE        0x00000010
>     #define SQLITE_OPEN_MAIN_DB          0x00000100
>     #define SQLITE_OPEN_TEMP_DB          0x00000200
>     #define SQLITE_OPEN_TRANSIENT_DB     0x00000400
>     #define SQLITE_OPEN_MAIN_JOURNAL     0x00000800
>     #define SQLITE_OPEN_TEMP_JOURNAL     0x00001000
>     #define SQLITE_OPEN_SUBJOURNAL       0x00002000
>     #define SQLITE_OPEN_MASTER_JOURNAL   0x00004000

These bit values are intended for use in then 3rd parameter to the sqlite3_open_v2() interface and in the 4th parameter to the xOpen method of the sqlite3_vfs object.

## Constants Defining Special Destructor Behavior

>     typedef void (*sqlite3_destructor_type)(void*);
>     #define SQLITE_STATIC      ((sqlite3_destructor_type)0)
>     #define SQLITE_TRANSIENT   ((sqlite3_destructor_type)-1)

These are special value for the destructor that is passed in as the final argument to routines like sqlite3_result_blob(). If the destructor argument is SQLITE_STATIC, it means that the content pointer is constant and will never change. It does not need to be destroyed. The SQLITE_TRANSIENT value means that the content will likely change in the near future and that SQLite should make its own private copy of the content before returning.

The typedef is necessary to work around problems in certain C++ compilers. See ticket #2191.

## Synchronization Type Flags

>     #define SQLITE_SYNC_NORMAL        0x00002
>     #define SQLITE_SYNC_FULL          0x00003
>     #define SQLITE_SYNC_DATAONLY      0x00010

When SQLite invokes the xSync() method of an sqlite3_io_methods object it uses a combination of the these integer values as the second argument.

When the SQLITE_SYNC_DATAONLY flag is used, it means that the sync operation only needs to flush data to mass storage. Inode information need not be flushed. The SQLITE_SYNC_NORMAL means to use normal fsync() semantics. The SQLITE_SYNC_FULL flag means to use Mac OS-X style fullsync instead of fsync().

## Testing Interface Operation Codes

>     #define SQLITE_TESTCTRL_FAULT_CONFIG             1
>     #define SQLITE_TESTCTRL_FAULT_FAILURES           2
>     #define SQLITE_TESTCTRL_FAULT_BENIGN_FAILURES    3
>     #define SQLITE_TESTCTRL_FAULT_PENDING            4

These constants are the valid operation code parameters used as the first argument to sqlite3_test_control().

These parameters and their meansing are subject to change without notice. These values are for testing purposes only. Applications should not use any of these parameters or the sqlite3_test_control() interface.

## Compile-Time Library Version Numbers

>     #define SQLITE_VERSION         "3.5.6"
>     #define SQLITE_VERSION_NUMBER 3005006

The SQLITE_VERSION and SQLITE_VERSION_NUMBER #defines in the sqlite3.h file specify the version of SQLite with which that header file is associated.

The "version" of SQLite is a strong of the form "X.Y.Z". The phrase "alpha" or "beta" might be appended after the Z. The X value is major version number always 3 in SQLite3. The X value only changes when backwards compatibility is broken and we intend to never break backwards compatibility. The Y value is the minor version number and only changes when there are major feature enhancements that are forwards compatible but not backwards compatible. The Z value is release number and is incremented with each release but resets back to 0 when Y is incremented.

See also: sqlite3_libversion() and sqlite3_libversion_number().

### Invariants:

F10011 | The SQLITE_VERSION #define in the sqlite3.h header file evaluates to a string literal that is the SQLite version with which the header file is associated.
F10014 | The SQLITE_VERSION_NUMBER #define resolves to an integer with the value (X*1000000 + Y*1000 + Z) where X, Y, and Z are the major version, minor version, and release number.

## 64-Bit Integer Types

>     #ifdef SQLITE_INT64_TYPE
>       typedef SQLITE_INT64_TYPE sqlite_int64;
>       typedef unsigned SQLITE_INT64_TYPE sqlite_uint64;
>     #elif defined(_MSC_VER) || defined(__BORLANDC__)
>       typedef __int64 sqlite_int64;
>       typedef unsigned __int64 sqlite_uint64;
>     #else
>       typedef long long int sqlite_int64;
>       typedef unsigned long long int sqlite_uint64;
>     #endif
>     typedef sqlite_int64 sqlite3_int64;
>     typedef sqlite_uint64 sqlite3_uint64;

Because there is no cross-platform way to specify 64-bit integer types SQLite includes typedefs for 64-bit signed and unsigned integers.

The sqlite3_int64 and sqlite3_uint64 are the preferred type definitions. The sqlite_int64 and sqlite_uint64 types are supported for backwards compatibility only.

### Invariants:

F10201 | The sqlite_int64 and sqlite3_int64 types specify a 64-bit signed integer.
F10202 | The sqlite_uint64 and sqlite3_uint64 types specify a 64-bit unsigned integer.

## Database Connection Handle

>     typedef struct sqlite3 sqlite3;

Each open SQLite database is represented by pointer to an instance of the opaque structure named "sqlite3". It is useful to think of an sqlite3 pointer as an object. The sqlite3_open(), sqlite3_open16(), and sqlite3_open_v2() interfaces are its constructors and sqlite3_close() is its destructor. There are many other interfaces (such as sqlite3_prepare_v2(), sqlite3_create_function(), and sqlite3_busy_timeout() to name but three) that are methods on this object.

## SQL Statement Object

>     typedef struct sqlite3_stmt sqlite3_stmt;

An instance of this object represent single SQL statements. This object is variously known as a "prepared statement" or a "compiled SQL statement" or simply as a "statement".

The life of a statement object goes something like this:

1. Create the object using sqlite3_prepare_v2() or a related function.
2. Bind values to host parameters using sqlite3_bind_* interfaces.
3. Run the SQL by calling sqlite3_step() one or more times.
4. Reset the statement using sqlite3_reset() then go back to step 2. Do this zero or more times.
5. Destroy the object using sqlite3_finalize().

Refer to documentation on individual methods above for additional information.

## Obsolete Functions

>     int sqlite3_aggregate_count(sqlite3_context*);
>     int sqlite3_expired(sqlite3_stmt*);
>     int sqlite3_transfer_bindings(sqlite3_stmt*, sqlite3_stmt*);
>     int sqlite3_global_recover(void);
>     void sqlite3_thread_cleanup(void);
>     int sqlite3_memory_alarm(void(*)(void*,sqlite3_int64,int),void*,sqlite3_int64);

These functions are all now obsolete. In order to maintain backwards compatibility with older code, we continue to support these functions. However, new development projects should avoid the use of these functions. To help encourage people to avoid using these functions, we are not going to tell you want they do.

## Binding Values To Prepared Statements

>     int sqlite3_bind_blob(sqlite3_stmt*, int, const void*, int n, void(*)(void*));
>     int sqlite3_bind_double(sqlite3_stmt*, int, double);
>     int sqlite3_bind_int(sqlite3_stmt*, int, int);
>     int sqlite3_bind_int64(sqlite3_stmt*, int, sqlite3_int64);
>     int sqlite3_bind_null(sqlite3_stmt*, int);
>     int sqlite3_bind_text(sqlite3_stmt*, int, const char*, int n, void(*)(void*));
>     int sqlite3_bind_text16(sqlite3_stmt*, int, const void*, int, void(*)(void*));
>     int sqlite3_bind_value(sqlite3_stmt*, int, const sqlite3_value*);
>     int sqlite3_bind_zeroblob(sqlite3_stmt*, int, int n);

In the SQL strings input to sqlite3_prepare_v2() and its variants, literals may be replace by a parameter in one of these forms:

- ?
- ?NNN
- :VVV
- @VVV
- $VVV

In the parameter forms shown above NNN is an integer literal, VVV alpha-numeric parameter name. The values of these parameters (also called "host parameter names" or "SQL parameters") can be set using the sqlite3_bind_*() routines defined here.

The first argument to the sqlite3_bind_*() routines always is a pointer to the sqlite3_stmt object returned from sqlite3_prepare_v2() or its variants. The second argument is the index of the parameter to be set. The first parameter has an index of 1. When the same named parameter is used more than once, second and subsequent occurrences have the same index as the first occurrence. The index for named parameters can be looked up using the sqlite3_bind_parameter_name() API if desired. The index for "?NNN" parameters is the value of NNN. The NNN value must be between 1 and the compile-time parameter SQLITE_MAX_VARIABLE_NUMBER (default value: 999).

The third argument is the value to bind to the parameter.

In those routines that have a fourth argument, its value is the number of bytes in the parameter. To be clear: the value is the number of bytes in the value, not the number of characters. The number of bytes does not include the zero-terminator at the end of strings. If the fourth parameter is negative, the length of the string is number of bytes up to the first zero terminator.

The fifth argument to sqlite3_bind_blob(), sqlite3_bind_text(), and sqlite3_bind_text16() is a destructor used to dispose of the BLOB or string after SQLite has finished with it. If the fifth argument is the special value SQLITE_STATIC, then SQLite assumes that the information is in static, unmanaged space and does not need to be freed. If the fifth argument has the value SQLITE_TRANSIENT, then SQLite makes its own private copy of the data immediately, before the sqlite3_bind_*() routine returns.

The sqlite3_bind_zeroblob() routine binds a BLOB of length N that is filled with zeros. A zeroblob uses a fixed amount of memory (just an integer to hold it size) while it is being processed. Zeroblobs are intended to serve as place-holders for BLOBs whose content is later written using increment BLOB I/O routines. A negative value for the zeroblob results in a zero-length BLOB.

The sqlite3_bind_*() routines must be called after sqlite3_prepare_v2() (and its variants) or sqlite3_reset() and before sqlite3_step(). Bindings are not cleared by the sqlite3_reset() routine. Unbound parameters are interpreted as NULL.

These routines return SQLITE_OK on success or an error code if anything goes wrong. SQLITE_RANGE is returned if the parameter index is out of range. SQLITE_NOMEM is returned if malloc fails. SQLITE_MISUSE might be returned if these routines are called on a virtual machine that is the wrong state or which has already been finalized. Detection of misuse is unreliable. Applications should not depend on SQLITE_MISUSE returns. SQLITE_MISUSE is intended to indicate a a logic error in the application. Future versions of SQLite might panic rather than return SQLITE_MISUSE.

See also: sqlite3_bind_parameter_count(), sqlite3_bind_parameter_name(), and sqlite3_bind_parameter_index().

### Invariants:

F13506 | The SQL statement compiler recognizes tokens of the forms "?", "?NNN", "$VVV", ":VVV", and "@VVV" as SQL parameters, where NNN is any sequence of one or more digits and where VVV is any sequence of one or more alphanumeric characters or "::" optionally followed by a string containing no spaces and contained within parentheses.
F13509 | The initial value of an SQL parameter is NULL.
F13512 | The index of an "?" SQL parameter is one larger than the largest index of SQL parameter to the left, or 1 if the "?" is the leftmost SQL parameter.
F13515 | The index of an "?NNN" SQL parameter is the integer NNN.
F13518 | The index of an ":VVV", "$VVV", or "@VVV" SQL parameter is the same as the index of leftmost occurances of the same parameter, or one more than the largest index over all parameters to the left if this is the first occurrance of this parameter, or 1 if this is the leftmost parameter.
F13521 | The SQL statement compiler fail with an SQLITE_RANGE error if the index of an SQL parameter is less than 1 or greater than SQLITE_MAX_VARIABLE_NUMBER.
F13524 | Calls to sqlite3_bind(S,N,V,...) associate the value V with all SQL parameters having an index of N in the prepared statement S.
F13527 | Calls to sqlite3_bind(S,N,...) override prior calls with the same values of S and N.
F13530 | Bindings established by sqlite3_bind(S,...) persist across calls to sqlite3_reset(S).
F13533 | In calls to sqlite3_bind_blob(S,N,V,L,D), sqlite3_bind_text(S,N,V,L,D), or sqlite3_bind_text16(S,N,V,L,D) SQLite binds the first L bytes of the blob or string pointed to by V, when L is non-negative.
F13536 | In calls to sqlite3_bind_text(S,N,V,L,D) or sqlite3_bind_text16(S,N,V,L,D) SQLite binds characters from V through the first zero character when L is negative.
F13539 | In calls to sqlite3_bind_blob(S,N,V,L,D), sqlite3_bind_text(S,N,V,L,D), or sqlite3_bind_text16(S,N,V,L,D) when D is the special constant SQLITE_STATIC, SQLite assumes that the value V is held in static unmanaged space that will not change during the lifetime of the binding.
F13542 | In calls to sqlite3_bind_blob(S,N,V,L,D), sqlite3_bind_text(S,N,V,L,D), or sqlite3_bind_text16(S,N,V,L,D) when D is the special constant SQLITE_TRANSIENT, the routine makes a private copy of V value before it returns.
F13545 | In calls to sqlite3_bind_blob(S,N,V,L,D), sqlite3_bind_text(S,N,V,L,D), or sqlite3_bind_text16(S,N,V,L,D) when D is a pointer to a function, SQLite invokes that function to destroy the V value after it has finished using the V value.
F13548 | In calls to sqlite3_bind_zeroblob(S,N,V,L) the value bound is a blob of L bytes, or a zero-length blob if L is negative.

## Collation Needed Callbacks

>     int sqlite3_collation_needed(
>       sqlite3*,
>       void*,
>       void(*)(void*,sqlite3*,int eTextRep,const char*)
>     );
>     int sqlite3_collation_needed16(
>       sqlite3*,
>       void*,
>       void(*)(void*,sqlite3*,int eTextRep,const void*)
>     );

To avoid having to register all collation sequences before a database can be used, a single callback function may be registered with the database handle to be called whenever an undefined collation sequence is required.

If the function is registered using the sqlite3_collation_needed() API, then it is passed the names of undefined collation sequences as strings encoded in UTF-8. If sqlite3_collation_needed16() is used, the names are passed as UTF-16 in machine native byte order. A call to either function replaces any existing callback.

When the callback is invoked, the first argument passed is a copy of the second argument to sqlite3_collation_needed() or sqlite3_collation_needed16(). The second argument is the database handle. The third argument is one of SQLITE_UTF8, SQLITE_UTF16BE, or SQLITE_UTF16LE, indicating the most desirable form of the collation sequence function required. The fourth parameter is the name of the required collation sequence.

The callback function should register the desired collation using sqlite3_create_collation(), sqlite3_create_collation16(), or sqlite3_create_collation_v2().

## Results Values From A Query

>     const void *sqlite3_column_blob(sqlite3_stmt*, int iCol);
>     int sqlite3_column_bytes(sqlite3_stmt*, int iCol);
>     int sqlite3_column_bytes16(sqlite3_stmt*, int iCol);
>     double sqlite3_column_double(sqlite3_stmt*, int iCol);
>     int sqlite3_column_int(sqlite3_stmt*, int iCol);
>     sqlite3_int64 sqlite3_column_int64(sqlite3_stmt*, int iCol);
>     const unsigned char *sqlite3_column_text(sqlite3_stmt*, int iCol);
>     const void *sqlite3_column_text16(sqlite3_stmt*, int iCol);
>     int sqlite3_column_type(sqlite3_stmt*, int iCol);
>     sqlite3_value *sqlite3_column_value(sqlite3_stmt*, int iCol);

These routines form the "result set query" interface.

These routines return information about a single column of the current result row of a query. In every case the first argument is a pointer to the prepared statement that is being evaluated (the sqlite3_stmt* that was returned from sqlite3_prepare_v2() or one of its variants) and the second argument is the index of the column for which information should be returned. The left-most column of the result set has an index of 0.

If the SQL statement is not currently point to a valid row, or if the the column index is out of range, the result is undefined. These routines may only be called when the most recent call to sqlite3_step() has returned SQLITE_ROW and neither sqlite3_reset() nor sqlite3_finalize() has been call subsequently. If any of these routines are called after sqlite3_reset() or sqlite3_finalize() or after sqlite3_step() has returned something other than SQLITE_ROW, the results are undefined. If sqlite3_step() or sqlite3_reset() or sqlite3_finalize() are called from a different thread while any of these routines are pending, then the results are undefined.

The sqlite3_column_type() routine returns datatype code for the initial data type of the result column. The returned value is one of SQLITE_INTEGER, SQLITE_FLOAT, SQLITE_TEXT, SQLITE_BLOB, or SQLITE_NULL. The value returned by sqlite3_column_type() is only meaningful if no type conversions have occurred as described below. After a type conversion, the value returned by sqlite3_column_type() is undefined. Future versions of SQLite may change the behavior of sqlite3_column_type() following a type conversion.

If the result is a BLOB or UTF-8 string then the sqlite3_column_bytes() routine returns the number of bytes in that BLOB or string. If the result is a UTF-16 string, then sqlite3_column_bytes() converts the string to UTF-8 and then returns the number of bytes. If the result is a numeric value then sqlite3_column_bytes() uses sqlite3_snprintf() to convert that value to a UTF-8 string and returns the number of bytes in that string. The value returned does not include the zero terminator at the end of the string. For clarity: the value returned is the number of bytes in the string, not the number of characters.

Strings returned by sqlite3_column_text() and sqlite3_column_text16(), even empty strings, are always zero terminated. The return value from sqlite3_column_blob() for a zero-length blob is an arbitrary pointer, possibly even a NULL pointer.

The sqlite3_column_bytes16() routine is similar to sqlite3_column_bytes() but leaves the result in UTF-16 in native byte order instead of UTF-8. The zero terminator is not included in this count.

These routines attempt to convert the value where appropriate. For example, if the internal representation is FLOAT and a text result is requested, sqlite3_snprintf() is used internally to do the conversion automatically. The following table details the conversions that are applied:

> Internal Type | Requested Type | Conversion
> --- | --- | ---
> NULL | INTEGER | Result is 0
> NULL | FLOAT | Result is 0.0
> NULL | TEXT | Result is NULL pointer
> NULL | BLOB | Result is NULL pointer
> INTEGER | FLOAT | Convert from integer to float
> INTEGER | TEXT | ASCII rendering of the integer
> INTEGER | BLOB | Same as for INTEGER->TEXT
> FLOAT | INTEGER | Convert from float to integer
> FLOAT | TEXT | ASCII rendering of the float
> FLOAT | BLOB | Same as FLOAT->TEXT
> TEXT | INTEGER | Use atoi()
> TEXT | FLOAT | Use atof()
> TEXT | BLOB | No change
> BLOB | INTEGER | Convert to TEXT then use atoi()
> BLOB | FLOAT | Convert to TEXT then use atof()
> BLOB | TEXT | Add a zero terminator if needed

The table above makes reference to standard C library functions atoi() and atof(). SQLite does not really use these functions. It has its on equavalent internal routines. The atoi() and atof() names are used in the table for brevity and because they are familiar to most C programmers.

Note that when type conversions occur, pointers returned by prior calls to sqlite3_column_blob(), sqlite3_column_text(), and/or sqlite3_column_text16() may be invalidated. Type conversions and pointer invalidations might occur in the following cases:

- The initial content is a BLOB and sqlite3_column_text() or sqlite3_column_text16() is called. A zero-terminator might need to be added to the string.

- The initial content is UTF-8 text and sqlite3_column_bytes16() or sqlite3_column_text16() is called. The content must be converted to UTF-16.

- The initial content is UTF-16 text and sqlite3_column_bytes() or sqlite3_column_text() is called. The content must be converted to UTF-8.

Conversions between UTF-16be and UTF-16le are always done in place and do not invalidate a prior pointer, though of course the content of the buffer that the prior pointer points to will have been modified. Other kinds of conversion are done in place when it is possible, but sometime it is not possible and in those cases prior pointers are invalidated.

The safest and easiest to remember policy is to invoke these routines in one of the following ways:

- sqlite3_column_text() followed by sqlite3_column_bytes()
- sqlite3_column_blob() followed by sqlite3_column_bytes()
- sqlite3_column_text16() followed by sqlite3_column_bytes16()

In other words, you should call sqlite3_column_text(), sqlite3_column_blob(), or sqlite3_column_text16() first to force the result into the desired format, then invoke sqlite3_column_bytes() or sqlite3_column_bytes16() to find the size of the result. Do not mix call to sqlite3_column_text() or sqlite3_column_blob() with calls to sqlite3_column_bytes16(). And do not mix calls to sqlite3_column_text16() with calls to sqlite3_column_bytes().

The pointers returned are valid until a type conversion occurs as described above, or until sqlite3_step() or sqlite3_reset() or sqlite3_finalize() is called. The memory space used to hold strings and blobs is freed automatically. Do not pass the pointers returned sqlite3_column_blob(), sqlite3_column_text(), etc. into sqlite3_free().

If a memory allocation error occurs during the evaluation of any of these routines, a default value is returned. The default value is either the integer 0, the floating point number 0.0, or a NULL pointer. Subsequent calls to sqlite3_errcode() will return SQLITE_NOMEM.

### Invariants:

F13803 | The sqlite3_column_blob(S,N) interface converts the Nth column in the current row of the result set for prepared statement S into a blob and then returns a pointer to the converted value.
F13806 | The sqlite3_column_bytes(S,N) interface returns the number of bytes in the blob or string (exclusive of the zero terminator on the string) that was returned by the most recent call to sqlite3_column_blob(S,N) or sqlite3_column_text(S,N).
F13809 | The sqlite3_column_bytes16(S,N) interface returns the number of bytes in the string (exclusive of the zero terminator on the string) that was returned by the most recent call to sqlite3_column_text16(S,N).
F13812 | The sqlite3_column_double(S,N) interface converts the Nth column in the current row of the result set for prepared statement S into a floating point value and returns a copy of that value.
F13815 | The sqlite3_column_int(S,N) interface converts the Nth column in the current row of the result set for prepared statement S into a 32-bit signed integer and returns a copy of that integer.
F13818 | The sqlite3_column_int64(S,N) interface converts the Nth column in the current row of the result set for prepared statement S into a 64-bit signed integer and returns a copy of that integer.
F13821 | The sqlite3_column_text(S,N) interface converts the Nth column in the current row of the result set for prepared statement S into a zero-terminated UTF-8 string and returns a pointer to that string.
F13824 | The sqlite3_column_text16(S,N) interface converts the Nth column in the current row of the result set for prepared statement S into a zero-terminated 2-byte aligned UTF-16 native byte order string and returns a pointer to that string.
F13827 | The sqlite3_column_type(S,N) interface returns one of SQLITE_NULL, SQLITE_INTEGER, SQLITE_FLOAT, SQLITE_TEXT, or SQLITE_BLOB as appropriate for the Nth column in the current row of the result set for prepared statement S.
F13830 | The sqlite3_column_value(S,N) interface returns a pointer to the sqlite3_value object that for the Nth column in the current row of the result set for prepared statement S.

## Source Of Data In A Query Result

>     const char *sqlite3_column_database_name(sqlite3_stmt*,int);
>     const void *sqlite3_column_database_name16(sqlite3_stmt*,int);
>     const char *sqlite3_column_table_name(sqlite3_stmt*,int);
>     const void *sqlite3_column_table_name16(sqlite3_stmt*,int);
>     const char *sqlite3_column_origin_name(sqlite3_stmt*,int);
>     const void *sqlite3_column_origin_name16(sqlite3_stmt*,int);

These routines provide a means to determine what column of what table in which database a result of a SELECT statement comes from. The name of the database or table or column can be returned as either a UTF8 or UTF16 string. The _database_ routines return the database name, the _table_ routines return the table name, and the origin_ routines return the column name. The returned string is valid until the prepared statement is destroyed using sqlite3_finalize() or until the same information is requested again in a different encoding.

The names returned are the original un-aliased names of the database, table, and column.

The first argument to the following calls is a prepared statement. These functions return information about the Nth column returned by the statement, where N is the second function argument.

If the Nth column returned by the statement is an expression or subquery and is not a column value, then all of these functions return NULL. These routine might also return NULL if a memory allocation error occurs. Otherwise, they return the name of the attached database, table and column that query result column was extracted from.

As with all other SQLite APIs, those postfixed with "16" return UTF-16 encoded strings, the other functions return UTF-8.

These APIs are only available if the library was compiled with the SQLITE_ENABLE_COLUMN_METADATA preprocessor symbol defined.

If two or more threads call one or more of these routines against the same prepared statement and column at the same time then the results are undefined.

### Invariants:

F13741 | The sqlite3_column_database_name(S,N) interface returns either the UTF-8 zero-terminated name of the database from which the Nth result column of prepared statement S is extracted, or NULL if the the Nth column of S is a general expression or if unable to allocate memory to store the name.
F13742 | The sqlite3_column_database_name16(S,N) interface returns either the UTF-16 native byte order zero-terminated name of the database from which the Nth result column of prepared statement S is extracted, or NULL if the the Nth column of S is a general expression or if unable to allocate memory to store the name.
F13743 | The sqlite3_column_table_name(S,N) interface returns either the UTF-8 zero-terminated name of the table from which the Nth result column of prepared statement S is extracted, or NULL if the the Nth column of S is a general expression or if unable to allocate memory to store the name.
F13744 | The sqlite3_column_table_name16(S,N) interface returns either the UTF-16 native byte order zero-terminated name of the table from which the Nth result column of prepared statement S is extracted, or NULL if the the Nth column of S is a general expression or if unable to allocate memory to store the name.
F13745 | The sqlite3_column_origin_name(S,N) interface returns either the UTF-8 zero-terminated name of the table column from which the Nth result column of prepared statement S is extracted, or NULL if the the Nth column of S is a general expression or if unable to allocate memory to store the name.
F13746 | The sqlite3_column_origin_name16(S,N) interface returns either the UTF-16 native byte order zero-terminated name of the table column from which the Nth result column of prepared statement S is extracted, or NULL if the the Nth column of S is a general expression or if unable to allocate memory to store the name.
F13748 | The return values from column metadata interfaces are valid for the lifetime of the prepared statement or until the encoding is changed by another metadata interface call for the same prepared statement and column.

### Limitations:

U13751 | If two or more threads call one or more column metadata interfaces the same prepared statement and result column at the same time then the results are undefined.

## Declared Datatype Of A Query Result

>     const char *sqlite3_column_decltype(sqlite3_stmt*,int);
>     const void *sqlite3_column_decltype16(sqlite3_stmt*,int);

The first parameter is a prepared statement. If this statement is a SELECT statement and the Nth column of the returned result set of that SELECT is a table column (not an expression or subquery) then the declared type of the table column is returned. If the Nth column of the result set is an expression or subquery, then a NULL pointer is returned. The returned string is always UTF-8 encoded. For example, in the database schema:

CREATE TABLE t1(c1 VARIANT);

And the following statement compiled:

SELECT c1 + 1, c1 FROM t1;

Then this routine would return the string "VARIANT" for the second result column (i==1), and a NULL pointer for the first result column (i==0).

SQLite uses dynamic run-time typing. So just because a column is declared to contain a particular type does not mean that the data stored in that column is of the declared type. SQLite is strongly typed, but the typing is dynamic not static. Type is associated with individual values, not with the containers used to hold those values.

### Invariants:

F13761 | A successful call to sqlite3_column_decltype(S,N) returns a zero-terminated UTF-8 string containing the the declared datatype of the table column that appears as the Nth column (numbered from 0) of the result set to the prepared statement S.
F13762 | A successful call to sqlite3_column_decltype16(S,N) returns a zero-terminated UTF-16 native byte order string containing the declared datatype of the table column that appears as the Nth column (numbered from 0) of the result set to the prepared statement S.
F13763 | If N is less than 0 or N is greater than or equal to the number of columns in prepared statement S or if the Nth column of S is an expression or subquery rather than a table column or if a memory allocation failure occurs during encoding conversions, then calls to sqlite3_column_decltype(S,N) or sqlite3_column_decltype16(S,N) return NULL.

## Column Names In A Result Set

>     const char *sqlite3_column_name(sqlite3_stmt*, int N);
>     const void *sqlite3_column_name16(sqlite3_stmt*, int N);

These routines return the name assigned to a particular column in the result set of a SELECT statement. The sqlite3_column_name() interface returns a pointer to a zero-terminated UTF8 string and sqlite3_column_name16() returns a pointer to a zero-terminated UTF16 string. The first parameter is the prepared statement that implements the SELECT statement. The second parameter is the column number. The left-most column is number 0.

The returned string pointer is valid until either the prepared statement is destroyed by sqlite3_finalize() or until the next call sqlite3_column_name() or sqlite3_column_name16() on the same column.

If sqlite3_malloc() fails during the processing of either routine (for example during a conversion from UTF-8 to UTF-16) then a NULL pointer is returned.

The name of a result column is the value of the "AS" clause for that column, if there is an AS clause. If there is no AS clause then the name of the column is unspecified and may change from one release of SQLite to the next.

### Invariants:

F13721 | A successful invocation of the sqlite3_column_name(S,N) interface returns the name of the Nth column (where 0 is the left-most column) for the result set of prepared statement S as a zero-terminated UTF-8 string.
F13723 | A successful invocation of the sqlite3_column_name16(S,N) interface returns the name of the Nth column (where 0 is the left-most column) for the result set of prepared statement S as a zero-terminated UTF-16 string in the native byte order.
F13724 | The sqlite3_column_name() and sqlite3_column_name16() interfaces return a NULL pointer if they are unable to allocate memory memory to hold there normal return strings.
F13725 | If the N parameter to sqlite3_column_name(S,N) or sqlite3_column_name16(S,N) is out of range, then the interfaces returns a NULL pointer.
F13726 | The strings returned by sqlite3_column_name(S,N) and sqlite3_column_name16(S,N) are valid until the next call to either routine with the same S and N parameters or until sqlite3_finalize(S) is called.
F13727 | When a result column of a SELECT statement contains an AS clause, the name of that column is the indentifier to the right of the AS keyword.

## Commit And Rollback Notification Callbacks

>     void *sqlite3_commit_hook(sqlite3*, int(*)(void*), void*);
>     void *sqlite3_rollback_hook(sqlite3*, void(*)(void *), void*);

The sqlite3_commit_hook() interface registers a callback function to be invoked whenever a transaction is committed. Any callback set by a previous call to sqlite3_commit_hook() for the same database connection is overridden. The sqlite3_rollback_hook() interface registers a callback function to be invoked whenever a transaction is committed. Any callback set by a previous call to sqlite3_commit_hook() for the same database connection is overridden. The pArg argument is passed through to the callback. If the callback on a commit hook function returns non-zero, then the commit is converted into a rollback.

If another function was previously registered, its pArg value is returned. Otherwise NULL is returned.

Registering a NULL function disables the callback.

For the purposes of this API, a transaction is said to have been rolled back if an explicit "ROLLBACK" statement is executed, or an error or constraint causes an implicit rollback to occur. The rollback callback is not invoked if a transaction is automatically rolled back because the database connection is closed. The rollback callback is not invoked if a transaction is rolled back because a commit callback returned non-zero. (TODO: Check on this )

These are experimental interfaces and are subject to change.

## Determine If An SQL Statement Is Complete

>     int sqlite3_complete(const char *sql);
>     int sqlite3_complete16(const void *sql);

These routines are useful for command-line input to determine if the currently entered text seems to form complete a SQL statement or if additional input is needed before sending the text into SQLite for parsing. These routines return true if the input string appears to be a complete SQL statement. A statement is judged to be complete if it ends with a semicolon token and is not a fragment of a CREATE TRIGGER statement. Semicolons that are embedded within string literals or quoted identifier names or comments are not independent tokens (they are part of the token in which they are embedded) and thus do not count as a statement terminator.

These routines do not parse the SQL and so will not detect syntactically incorrect SQL.

### Invariants:

F10511 | The sqlite3_complete() and sqlite3_complete16() functions return true (non-zero) if and only if the last non-whitespace token in their input is a semicolon that is not in between the BEGIN and END of a CREATE TRIGGER statement.

### Limitations:

U10512 | The input to sqlite3_complete() must be a zero-terminated UTF-8 string.
U10513 | The input to sqlite3_complete16() must be a zero-terminated UTF-16 string in native byte order.

## Define New Collating Sequences

>     int sqlite3_create_collation(
>       sqlite3*,
>       const char *zName,
>       int eTextRep,
>       void*,
>       int(*xCompare)(void*,int,const void*,int,const void*)
>     );
>     int sqlite3_create_collation_v2(
>       sqlite3*,
>       const char *zName,
>       int eTextRep,
>       void*,
>       int(*xCompare)(void*,int,const void*,int,const void*),
>       void(*xDestroy)(void*)
>     );
>     int sqlite3_create_collation16(
>       sqlite3*,
>       const char *zName,
>       int eTextRep,
>       void*,
>       int(*xCompare)(void*,int,const void*,int,const void*)
>     );

These functions are used to add new collation sequences to the sqlite3* handle specified as the first argument.

The name of the new collation sequence is specified as a UTF-8 string for sqlite3_create_collation() and sqlite3_create_collation_v2() and a UTF-16 string for sqlite3_create_collation16(). In all cases the name is passed as the second function argument.

The third argument may be one of the constants SQLITE_UTF8, SQLITE_UTF16LE or SQLITE_UTF16BE, indicating that the user-supplied routine expects to be passed pointers to strings encoded using UTF-8, UTF-16 little-endian or UTF-16 big-endian respectively. The third argument might also be SQLITE_UTF16_ALIGNED to indicate that the routine expects pointers to 16-bit word aligned strings of UTF16 in the native byte order of the host computer.

A pointer to the user supplied routine must be passed as the fifth argument. If it is NULL, this is the same as deleting the collation sequence (so that SQLite cannot call it anymore). Each time the application supplied function is invoked, it is passed a copy of the void* passed as the fourth argument to sqlite3_create_collation() or sqlite3_create_collation16() as its first parameter.

The remaining arguments to the application-supplied routine are two strings, each represented by a (length, data) pair and encoded in the encoding that was passed as the third argument when the collation sequence was registered. The application defined collation routine should return negative, zero or positive if the first string is less than, equal to, or greater than the second string. i.e. (STRING1 - STRING2).

The sqlite3_create_collation_v2() works like sqlite3_create_collation() excapt that it takes an extra argument which is a destructor for the collation. The destructor is called when the collation is destroyed and is passed a copy of the fourth parameter void* pointer of the sqlite3_create_collation_v2(). Collations are destroyed when they are overridden by later calls to the collation creation functions or when the sqlite3* database handle is closed using sqlite3_close().

## Error Codes And Messages

>     int sqlite3_errcode(sqlite3 *db);
>     const char *sqlite3_errmsg(sqlite3*);
>     const void *sqlite3_errmsg16(sqlite3*);

The sqlite3_errcode() interface returns the numeric result code or extended result code for the most recent failed sqlite3_* API call associated with sqlite3 handle 'db'. If a prior API call failed but the most recent API call succeeded, the return value from sqlite3_errcode() is undefined.

The sqlite3_errmsg() and sqlite3_errmsg16() return English-language text that describes the error, as either UTF8 or UTF16 respectively. Memory to hold the error message string is managed internally. The application does not need to worry with freeing the result. However, the error string might be overwritten or deallocated b subsequent calls to other SQLite interface functions.

### Invariants:

F12801 | The sqlite3_errcode(D) interface returns the numeric result code or extended result code for the most recent failed interface call associated with sqlite3 handle D.
U12802 | If a prior API call failed but the most recent API call succeeded, the return value from sqlite3_errcode(), sqlite3_errmsg(), and sqlite3_errmsg16() are undefined.
F12803 | The sqlite3_errmsg(D) and sqlite3_errmsg16(D) interfaces return English-language text that describes the error in the mostly recently failed interface call, encoded as either UTF8 or UTF16 respectively.
U12804 | The strings returned by sqlite3_errmsg() and sqlite3_errmsg16() are only valid until the next SQLite interface call.
F12807 | Calls to sqlite3_errcode(), sqlite3_errmsg(), and sqlite3_errmsg16() themselves do not affect the results of future invocations of these routines.
F12808 | Calls to API routines that do not return an error code (example: sqlite3_data_count()) do not change the error code or message returned by sqlite3_errcode(), sqlite3_errmsg(), or sqlite3_errmsg16().
F12809 | Interfaces that are not associated with a specific database connection (examples: sqlite3_mprintf() or sqlite3_enable_shared_cache() do not change the values returned by sqlite3_errcode(), sqlite3_errmsg(), or sqlite3_errmsg16().

## Memory Allocation Subsystem

>     void *sqlite3_malloc(int);
>     void *sqlite3_realloc(void*, int);
>     void sqlite3_free(void*);

The SQLite core uses these three routines for all of its own internal memory allocation needs. "Core" in the previous sentence does not include operating-system specific VFS implementation. The windows VFS uses native malloc and free for some operations.

The sqlite3_malloc() routine returns a pointer to a block of memory at least N bytes in length, where N is the parameter. If sqlite3_malloc() is unable to obtain sufficient free memory, it returns a NULL pointer. If the parameter N to sqlite3_malloc() is zero or negative then sqlite3_malloc() returns a NULL pointer.

Calling sqlite3_free() with a pointer previously returned by sqlite3_malloc() or sqlite3_realloc() releases that memory so that it might be reused. The sqlite3_free() routine is a no-op if is called with a NULL pointer. Passing a NULL pointer to sqlite3_free() is harmless. After being freed, memory should neither be read nor written. Even reading previously freed memory might result in a segmentation fault or other severe error. Memory corruption, a segmentation fault, or other severe error might result if sqlite3_free() is called with a non-NULL pointer that was not obtained from sqlite3_malloc() or sqlite3_free().

The sqlite3_realloc() interface attempts to resize a prior memory allocation to be at least N bytes, where N is the second parameter. The memory allocation to be resized is the first parameter. If the first parameter to sqlite3_realloc() is a NULL pointer then its behavior is identical to calling sqlite3_malloc(N) where N is the second parameter to sqlite3_realloc(). If the second parameter to sqlite3_realloc() is zero or negative then the behavior is exactly the same as calling sqlite3_free(P) where P is the first parameter to sqlite3_realloc(). Sqlite3_realloc() returns a pointer to a memory allocation of at least N bytes in size or NULL if sufficient memory is unavailable. If M is the size of the prior allocation, then min(N,M) bytes of the prior allocation are copied into the beginning of buffer returned by sqlite3_realloc() and the prior allocation is freed. If sqlite3_realloc() returns NULL, then the prior allocation is not freed.

The memory returned by sqlite3_malloc() and sqlite3_realloc() is always aligned to at least an 8 byte boundary.

The default implementation of the memory allocation subsystem uses the malloc(), realloc() and free() provided by the standard C library. However, if SQLite is compiled with the following C preprocessor macro

> SQLITE_MEMORY_SIZE=NNN

where NNN is an integer, then SQLite create a static array of at least NNN bytes in size and use that array for all of its dynamic memory allocation needs. Additional memory allocator options may be added in future releases.

In SQLite version 3.5.0 and 3.5.1, it was possible to define the SQLITE_OMIT_MEMORY_ALLOCATION which would cause the built-in implementation of these routines to be omitted. That capability is no longer provided. Only built-in memory allocators can be used.

The windows OS interface layer calls the system malloc() and free() directly when converting filenames between the UTF-8 encoding used by SQLite and whatever filename encoding is used by the particular windows installation. Memory allocation errors are detected, but they are reported back as SQLITE_CANTOPEN or SQLITE_IOERR rather than SQLITE_NOMEM.

### Invariants:

F17303 | The sqlite3_malloc(N) interface returns either a pointer to newly checked-out block of at least N bytes of memory that is 8-byte aligned, or it returns NULL if it is unable to fulfill the request.
F17304 | The sqlite3_malloc(N) interface returns a NULL pointer if N is less than or equal to zero.
F17305 | The sqlite3_free(P) interface releases memory previously returned from sqlite3_malloc() or sqlite3_realloc(), making it available for reuse.
F17306 | A call to sqlite3_free(NULL) is a harmless no-op.
F17310 | A call to sqlite3_realloc(0,N) is equivalent to a call to sqlite3_malloc(N).
F17312 | A call to sqlite3_realloc(P,0) is equivalent to a call to sqlite3_free(P).
F17315 | The SQLite core uses sqlite3_malloc(), sqlite3_realloc(), and sqlite3_free() for all of its memory allocation and deallocation needs.
F17318 | The sqlite3_realloc(P,N) interface returns either a pointer to a block of checked-out memory of at least N bytes in size that is 8-byte aligned, or a NULL pointer.
F17321 | When sqlite3_realloc(P,N) returns a non-NULL pointer, it first copies the first K bytes of content from P into the newly allocated where K is the lessor of N and the size of the buffer P.
F17322 | When sqlite3_realloc(P,N) returns a non-NULL pointer, it first releases the buffer P.
F17323 | When sqlite3_realloc(P,N) returns NULL, the buffer P is not modified or released.

### Limitations:

U17350 | The pointer arguments to sqlite3_free() and sqlite3_realloc() must be either NULL or else a pointer obtained from a prior invocation of sqlite3_malloc() or sqlite3_realloc() that has not been released.
U17351 | The application must not read or write any part of a block of memory after it has been released using sqlite3_free() or sqlite3_realloc().

## Convenience Routines For Running Queries

>     int sqlite3_get_table(
>       sqlite3*,             /* An open database */
>       const char *sql,      /* SQL to be evaluated */
>       char ***pResult,      /* Results of the query */
>       int *nrow,            /* Number of result rows written here */
>       int *ncolumn,         /* Number of result columns written here */
>       char **errmsg         /* Error msg written here */
>     );
>     void sqlite3_free_table(char **result);

Definition: A result table is memory data structure created by the sqlite3_get_table() interface. A result table records the complete query results from one or more queries.

The table conceptually has a number of rows and columns. But these numbers are not part of the result table itself. These numbers are obtained separately. Let N be the number of rows and M be the number of columns.

A result table is an array of pointers to zero-terminated UTF-8 strings. There are (N+1)*M elements in the array. The first M pointers point to zero-terminated strings that contain the names of the columns. The remaining entries all point to query results. NULL values are give a NULL pointer. All other values are in their UTF-8 zero-terminated string representation as returned by sqlite3_column_text().

A result table might consists of one or more memory allocations. It is not safe to pass a result table directly to sqlite3_free(). A result table should be deallocated using sqlite3_free_table().

As an example of the result table format, suppose a query result is as follows:

>     Name        | Age
>     -----------------------
>     Alice       | 43
>     Bob         | 28
>     Cindy       | 21

There are two column (M==2) and three rows (N==3). Thus the result table has 8 entries. Suppose the result table is stored in an array names azResult. Then azResult holds this content:

>     azResult[0] = "Name";
>     azResult[1] = "Age";
>     azResult[2] = "Alice";
>     azResult[3] = "43";
>     azResult[4] = "Bob";
>     azResult[5] = "28";
>     azResult[6] = "Cindy";
>     azResult[7] = "21";

The sqlite3_get_table() function evaluates one or more semicolon-separated SQL statements in the zero-terminated UTF-8 string of its 2nd parameter. It returns a result table to the pointer given in its 3rd parameter.

After the calling function has finished using the result, it should pass the pointer to the result table to sqlite3_free_table() in order to release the memory that was malloc-ed. Because of the way the sqlite3_malloc() happens within sqlite3_get_table(), the calling function must not try to call sqlite3_free() directly. Only sqlite3_free_table() is able to release the memory properly and safely.

The sqlite3_get_table() interface is implemented as a wrapper around sqlite3_exec(). The sqlite3_get_table() routine does not have access to any internal data structures of SQLite. It uses only the public interface defined here. As a consequence, errors that occur in the wrapper layer outside of the internal sqlite3_exec() call are not reflected in subsequent calls to sqlite3_errcode() or sqlite3_errmsg().

### Invariants:

F12371 | If a sqlite3_get_table() fails a memory allocation, then it frees the result table under construction, aborts the query in process, skips any subsequent queries, sets the *resultp output pointer to NULL and returns SQLITE_NOMEM.
F12373 | If the ncolumn parameter to sqlite3_get_table() is not NULL then sqlite3_get_table() write the number of columns in the result set of the query into *ncolumn if the query is successful (if the function returns SQLITE_OK).
F12374 | If the nrow parameter to sqlite3_get_table() is not NULL then sqlite3_get_table() write the number of rows in the result set of the query into *nrow if the query is successful (if the function returns SQLITE_OK).
F12376 | The sqlite3_get_table() function sets its *ncolumn value to the number of columns in the result set of the query in the sql parameter, or to zero if the query in sql has an empty result set.

## Function Auxiliary Data

>     void *sqlite3_get_auxdata(sqlite3_context*, int N);
>     void sqlite3_set_auxdata(sqlite3_context*, int N, void*, void (*)(void*));

The following two functions may be used by scalar SQL functions to associate meta-data with argument values. If the same value is passed to multiple invocations of the same SQL function during query execution, under some circumstances the associated meta-data may be preserved. This may be used, for example, to add a regular-expression matching scalar function. The compiled version of the regular expression is stored as meta-data associated with the SQL value passed as the regular expression pattern. The compiled regular expression can be reused on multiple invocations of the same function so that the original pattern string does not need to be recompiled on each invocation.

The sqlite3_get_auxdata() interface returns a pointer to the meta-data associated by the sqlite3_set_auxdata() function with the Nth argument value to the application-defined function. If no meta-data has been ever been set for the Nth argument of the function, or if the cooresponding function parameter has changed since the meta-data was set, then sqlite3_get_auxdata() returns a NULL pointer.

The sqlite3_set_auxdata() interface saves the meta-data pointed to by its 3rd parameter as the meta-data for the N-th argument of the application-defined function. Subsequent calls to sqlite3_get_auxdata() might return this data, if it has not been destroyed. If it is not NULL, SQLite will invoke the destructor function given by the 4th parameter to sqlite3_set_auxdata() on the meta-data when the corresponding function parameter changes or when the SQL statement completes, whichever comes first.

In practice, meta-data is preserved between function calls for expressions that are constant at compile time. This includes literal values and SQL variables.

These routines must be called from the same thread in which the SQL function is running.

## Run-Time Library Version Numbers

>     SQLITE_EXTERN const char sqlite3_version[];
>     const char *sqlite3_libversion(void);
>     int sqlite3_libversion_number(void);

These features provide the same information as the SQLITE_VERSION and SQLITE_VERSION_NUMBER #defines in the header, but are associated with the library instead of the header file. Cautious programmers might include a check in their application to verify that sqlite3_libversion_number() always returns the value SQLITE_VERSION_NUMBER.

The sqlite3_libversion() function returns the same information as is in the sqlite3_version [] string constant. The function is provided for use in DLLs since DLL users usually do not have direct access to string constants within the DLL.

### Invariants:

F10021 | The sqlite3_libversion_number() interface returns an integer equal to SQLITE_VERSION_NUMBER.
F10022 | The sqlite3_version string constant contains the text of the SQLITE_VERSION string.
F10023 | The sqlite3_libversion() function returns a pointer to the sqlite3_version string constant.

## Memory Allocator Statistics

>     sqlite3_int64 sqlite3_memory_used(void);
>     sqlite3_int64 sqlite3_memory_highwater(int resetFlag);

SQLite provides these two interfaces for reporting on the status of the sqlite3_malloc(), sqlite3_free(), and sqlite3_realloc() the memory allocation subsystem included within the SQLite.

### Invariants:

F17371 | The sqlite3_memory_used() routine returns the number of bytes of memory currently outstanding (malloced but not freed).
F17373 | The sqlite3_memory_highwater() routine returns the maximum value of sqlite3_memory_used() since the highwater mark was last reset.
F17374 | The values returned by sqlite3_memory_used() and sqlite3_memory_highwater() include any overhead added by SQLite in its implementation of sqlite3_malloc(), but not overhead added by the any underlying system library routines that sqlite3_malloc() may call.
F17375 | The memory highwater mark is reset to the current value of sqlite3_memory_used() if and only if the parameter to sqlite3_memory_highwater() is true. The value returned by sqlite3_memory_highwater(1) is the highwater mark prior to the reset.

## Formatted String Printing Functions

>     char *sqlite3_mprintf(const char*,...);
>     char *sqlite3_vmprintf(const char*, va_list);
>     char *sqlite3_snprintf(int,char*,const char*, ...);

These routines are workalikes of the "printf()" family of functions from the standard C library.

The sqlite3_mprintf() and sqlite3_vmprintf() routines write their results into memory obtained from sqlite3_malloc(). The strings returned by these two routines should be released by sqlite3_free(). Both routines return a NULL pointer if sqlite3_malloc() is unable to allocate enough memory to hold the resulting string.

In sqlite3_snprintf() routine is similar to "snprintf()" from the standard C library. The result is written into the buffer supplied as the second parameter whose size is given by the first parameter. Note that the order of the first two parameters is reversed from snprintf(). This is an historical accident that cannot be fixed without breaking backwards compatibility. Note also that sqlite3_snprintf() returns a pointer to its buffer instead of the number of characters actually written into the buffer. We admit that the number of characters written would be a more useful return value but we cannot change the implementation of sqlite3_snprintf() now without breaking compatibility.

As long as the buffer size is greater than zero, sqlite3_snprintf() guarantees that the buffer is always zero-terminated. The first parameter "n" is the total size of the buffer, including space for the zero terminator. So the longest string that can be completely written will be n-1 characters.

These routines all implement some additional formatting options that are useful for constructing SQL statements. All of the usual printf formatting options apply. In addition, there is are "%q", "%Q", and "%z" options.

The %q option works like %s in that it substitutes a null-terminated string from the argument list. But %q also doubles every '\'' character. %q is designed for use inside a string literal. By doubling each '\'' character it escapes that character and allows it to be inserted into the string.

For example, so some string variable contains text as follows:

>     char *zText = "It's a happy day!";

One can use this text in an SQL statement as follows:

>     char *zSQL = sqlite3_mprintf("INSERT INTO table VALUES('%q')", zText);
>     sqlite3_exec(db, zSQL, 0, 0, 0);
>     sqlite3_free(zSQL);

Because the %q format string is used, the '\'' character in zText is escaped and the SQL generated is as follows:

>     INSERT INTO table1 VALUES('It''s a happy day!')

This is correct. Had we used %s instead of %q, the generated SQL would have looked like this:

>     INSERT INTO table1 VALUES('It's a happy day!');

This second example is an SQL syntax error. As a general rule you should always use %q instead of %s when inserting text into a string literal.

The %Q option works like %q except it also adds single quotes around the outside of the total string. Or if the parameter in the argument list is a NULL pointer, %Q substitutes the text "NULL" (without single quotes) in place of the %Q option. So, for example, one could say:

>     char *zSQL = sqlite3_mprintf("INSERT INTO table VALUES(%Q)", zText);
>     sqlite3_exec(db, zSQL, 0, 0, 0);
>     sqlite3_free(zSQL);

The code above will render a correct SQL statement in the zSQL variable even if the zText variable is a NULL pointer.

The "%z" formatting option works exactly like "%s" with the addition that after the string has been read and copied into the result, sqlite3_free() is called on the input string.

### Invariants:

F17403 | The sqlite3_mprintf() and sqlite3_vmprintf() interfaces return either pointers to zero-terminated UTF-8 strings held in memory obtained from sqlite3_malloc() or NULL pointers if a call to sqlite3_malloc() fails.
F17406 | The sqlite3_snprintf() interface writes a zero-terminated UTF-8 string into the buffer pointed to by the second parameter provided that the first parameter is greater than zero.
F17407 | The sqlite3_snprintf() interface does not writes slots of its output buffer (the second parameter) outside the range of 0 through N-1 (where N is the first parameter) regardless of the length of the string requested by the format specification.

## Mutexes

>     sqlite3_mutex *sqlite3_mutex_alloc(int);
>     void sqlite3_mutex_free(sqlite3_mutex*);
>     void sqlite3_mutex_enter(sqlite3_mutex*);
>     int sqlite3_mutex_try(sqlite3_mutex*);
>     void sqlite3_mutex_leave(sqlite3_mutex*);

The SQLite core uses these routines for thread synchronization. Though they are intended for internal use by SQLite, code that links against SQLite is permitted to use any of these routines.

The SQLite source code contains multiple implementations of these mutex routines. An appropriate implementation is selected automatically at compile-time. The following implementations are available in the SQLite core:

- SQLITE_MUTEX_OS2
- SQLITE_MUTEX_PTHREAD
- SQLITE_MUTEX_W32
- SQLITE_MUTEX_NOOP

The SQLITE_MUTEX_NOOP implementation is a set of routines that does no real locking and is appropriate for use in a single-threaded application. The SQLITE_MUTEX_OS2, SQLITE_MUTEX_PTHREAD, and SQLITE_MUTEX_W32 implementations are appropriate for use on os/2, unix, and windows.

If SQLite is compiled with the SQLITE_MUTEX_APPDEF preprocessor macro defined (with "-DSQLITE_MUTEX_APPDEF=1"), then no mutex implementation is included with the library. The mutex interface routines defined here become external references in the SQLite library for which implementations must be provided by the application. This facility allows an application that links against SQLite to provide its own mutex implementation without having to modify the SQLite core.

The sqlite3_mutex_alloc() routine allocates a new mutex and returns a pointer to it. If it returns NULL that means that a mutex could not be allocated. SQLite will unwind its stack and return an error. The argument to sqlite3_mutex_alloc() is one of these integer constants:

- SQLITE_MUTEX_FAST
- SQLITE_MUTEX_RECURSIVE
- SQLITE_MUTEX_STATIC_MASTER
- SQLITE_MUTEX_STATIC_MEM
- SQLITE_MUTEX_STATIC_MEM2
- SQLITE_MUTEX_STATIC_PRNG
- SQLITE_MUTEX_STATIC_LRU

The first two constants cause sqlite3_mutex_alloc() to create a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE is used but not necessarily so when SQLITE_MUTEX_FAST is used. The mutex implementation does not need to make a distinction between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does not want to. But SQLite will only request a recursive mutex in cases where it really needs one. If a faster non-recursive mutex implementation is available on the host platform, the mutex subsystem might return such a mutex in response to SQLITE_MUTEX_FAST.

The other allowed parameters to sqlite3_mutex_alloc() each return a pointer to a static preexisting mutex. Four static mutexes are used by the current version of SQLite. Future versions of SQLite may add additional static mutexes. Static mutexes are for internal use by SQLite only. Applications that use SQLite mutexes should use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or SQLITE_MUTEX_RECURSIVE.

Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc() returns a different mutex on every call. But for the static mutex types, the same mutex is returned on every call that has the same type number.

The sqlite3_mutex_free() routine deallocates a previously allocated dynamic mutex. SQLite is careful to deallocate every dynamic mutex that it allocates. The dynamic mutexes must not be in use when they are deallocated. Attempting to deallocate a static mutex results in undefined behavior. SQLite never deallocates a static mutex.

The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt to enter a mutex. If another thread is already within the mutex, sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can be entered multiple times by the same thread. In such cases the, mutex must be exited an equal number of times before another thread can enter. If the same thread tries to enter any other kind of mutex more than once, the behavior is undefined. SQLite will never exhibit such behavior in its own use of mutexes.

Some systems (ex: windows95) do not the operation implemented by sqlite3_mutex_try(). On those systems, sqlite3_mutex_try() will always return SQLITE_BUSY. The SQLite core only ever uses sqlite3_mutex_try() as an optimization so this is acceptable behavior.

The sqlite3_mutex_leave() routine exits a mutex that was previously entered by the same thread. The behavior is undefined if the mutex is not currently entered by the calling thread or is not currently allocated. SQLite will never do either.

See also: sqlite3_mutex_held() and sqlite3_mutex_notheld().

## Mutex Verifcation Routines

>     int sqlite3_mutex_held(sqlite3_mutex*);
>     int sqlite3_mutex_notheld(sqlite3_mutex*);

The sqlite3_mutex_held() and sqlite3_mutex_notheld() routines are intended for use inside assert() statements. The SQLite core never uses these routines except inside an assert() and applications are advised to follow the lead of the core. The core only provides implementations for these routines when it is compiled with the SQLITE_DEBUG flag. External mutex implementations are only required to provide these routines if SQLITE_DEBUG is defined and if NDEBUG is not defined.

These routines should return true if the mutex in their argument is held or not held, respectively, by the calling thread.

The implementation is not required to provided versions of these routines that actually work. If the implementation does not provide working versions of these routines, it should at least provide stubs that always return true so that one does not get spurious assertion failures.

If the argument to sqlite3_mutex_held() is a NULL pointer then the routine should return 1. This seems counter-intuitive since clearly the mutex cannot be held if it does not exist. But the the reason the mutex does not exist is because the build is not using mutexes. And we do not want the assert() containing the call to sqlite3_mutex_held() to fail, so a non-zero return is the appropriate thing to do. The sqlite3_mutex_notheld() interface should also return 1 when given a NULL pointer.

## Opening A New Database Connection

>     int sqlite3_open(
>       const char *filename,   /* Database filename (UTF-8) */
>       sqlite3 **ppDb          /* OUT: SQLite db handle */
>     );
>     int sqlite3_open16(
>       const void *filename,   /* Database filename (UTF-16) */
>       sqlite3 **ppDb          /* OUT: SQLite db handle */
>     );
>     int sqlite3_open_v2(
>       const char *filename,   /* Database filename (UTF-8) */
>       sqlite3 **ppDb,         /* OUT: SQLite db handle */
>       int flags,              /* Flags */
>       const char *zVfs        /* Name of VFS module to use */
>     );

These routines open an SQLite database file whose name is given by the filename argument. The filename argument is interpreted as UTF-8 for sqlite3_open() and sqlite3_open_v2() and as UTF-16 in the native byte order for sqlite3_open16(). An sqlite3* handle is usually returned in *ppDb, even if an error occurs. The only exception is if SQLite is unable to allocate memory to hold the sqlite3 object, a NULL will be written into *ppDb instead of a pointer to the sqlite3 object. If the database is opened (and/or created) successfully, then SQLITE_OK is returned. Otherwise an error code is returned. The sqlite3_errmsg() or sqlite3_errmsg16() routines can be used to obtain an English language description of the error.

The default encoding for the database will be UTF-8 if sqlite3_open() or sqlite3_open_v2() is called and UTF-16 in the native byte order if sqlite3_open16() is used.

Whether or not an error occurs when it is opened, resources associated with the sqlite3* handle should be released by passing it to sqlite3_close() when it is no longer required.

The sqlite3_open_v2() interface works like sqlite3_open() except that it acccepts two additional parameters for additional control over the new database connection. The flags parameter can be one of:

1. SQLITE_OPEN_READONLY
2. SQLITE_OPEN_READWRITE
3. SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE

The first value opens the database read-only. If the database does not previously exist, an error is returned. The second option opens the database for reading and writing if possible, or reading only if if the file is write protected. In either case the database must already exist or an error is returned. The third option opens the database for reading and writing and creates it if it does not already exist. The third options is behavior that is always used for sqlite3_open() and sqlite3_open16().

If the filename is ":memory:", then an private in-memory database is created for the connection. This in-memory database will vanish when the database connection is closed. Future version of SQLite might make use of additional special filenames that begin with the ":" character. It is recommended that when a database filename really does begin with ":" that you prefix the filename with a pathname like "./" to avoid ambiguity.

If the filename is an empty string, then a private temporary on-disk database will be created. This private database will be automatically deleted as soon as the database connection is closed.

The fourth parameter to sqlite3_open_v2() is the name of the sqlite3_vfs object that defines the operating system interface that the new database connection should use. If the fourth parameter is a NULL pointer then the default sqlite3_vfs object is used.

Note to windows users: The encoding used for the filename argument of sqlite3_open() and sqlite3_open_v2() must be UTF-8, not whatever codepage is currently defined. Filenames containing international characters must be converted to UTF-8 prior to passing them into sqlite3_open() or sqlite3_open_v2().

### Invariants:

F12701 | The sqlite3_open(), sqlite3_open16(), and sqlite3_open_v2() interfaces create a new database connection associated with the database file given in their first parameter.
F12702 | The filename argument is interpreted as UTF-8 for sqlite3_open() and sqlite3_open_v2() and as UTF-16 in the native byte order for sqlite3_open16().
F12703 | A successful invocation of sqlite3_open(), sqlite3_open16(), or sqlite3_open_v2() writes a pointer to a new database connection into *ppDb.
F12704 | The sqlite3_open(), sqlite3_open16(), and sqlite3_open_v2() interfaces return SQLITE_OK upon success, or an appropriate error code on failure.
F12706 | The default text encoding for a new database created using sqlite3_open() or sqlite3_open_v2() will be UTF-8.
F12707 | The default text encoding for a new database created using sqlite3_open16() will be UTF-16.
F12709 | The sqlite3_open(F,D) interface is equivalent to sqlite3_open_v2(F,D,G,0) where the G parameter is SQLITE_OPEN_READWRITE| SQLITE_OPEN_CREATE.
F12711 | If the G parameter to sqlite3_open_v2(F,D,G,V) contains the bit value SQLITE_OPEN_READONLY then the database is opened for reading only.
F12712 | If the G parameter to sqlite3_open_v2(F,D,G,V) contains the bit value SQLITE_OPEN_READWRITE then the database is opened reading and writing if possible, or for reading only if the file is write protected by the operating system.
F12713 | If the G parameter to sqlite3_open(v2(F,D,G,V) omits the bit value SQLITE_OPEN_CREATE and the database does not previously exist, an error is returned.
F12714 | If the G parameter to sqlite3_open(v2(F,D,G,V) contains the bit value SQLITE_OPEN_CREATE and the database does not previously exist, then an attempt is made to create and initialize the database.
F12717 | If the filename argument to sqlite3_open(), sqlite3_open16(), or sqlite3_open_v2() is ":memory:", then an private, ephemeral, in-memory database is created for the connection. (TODO: Is SQLITE_OPEN_CREATE|SQLITE_OPEN_READWRITE required in sqlite3_open_v2()?)
F12719 | If the filename is an empty string, then a private, ephermeral on-disk database will be created. (TODO: Is SQLITE_OPEN_CREATE|SQLITE_OPEN_READWRITE required in sqlite3_open_v2()?)
F12721 | The database connection created by sqlite3_open_v2(F,D,G,V) will use the sqlite3_vfs object identified by the V parameter, or the default sqlite3_vfs object is V is a NULL pointer.

## Compiling An SQL Statement

>     int sqlite3_prepare(
>       sqlite3 *db,            /* Database handle */
>       const char *zSql,       /* SQL statement, UTF-8 encoded */
>       int nByte,              /* Maximum length of zSql in bytes. */
>       sqlite3_stmt **ppStmt,  /* OUT: Statement handle */
>       const char **pzTail     /* OUT: Pointer to unused portion of zSql */
>     );
>     int sqlite3_prepare_v2(
>       sqlite3 *db,            /* Database handle */
>       const char *zSql,       /* SQL statement, UTF-8 encoded */
>       int nByte,              /* Maximum length of zSql in bytes. */
>       sqlite3_stmt **ppStmt,  /* OUT: Statement handle */
>       const char **pzTail     /* OUT: Pointer to unused portion of zSql */
>     );
>     int sqlite3_prepare16(
>       sqlite3 *db,            /* Database handle */
>       const void *zSql,       /* SQL statement, UTF-16 encoded */
>       int nByte,              /* Maximum length of zSql in bytes. */
>       sqlite3_stmt **ppStmt,  /* OUT: Statement handle */
>       const void **pzTail     /* OUT: Pointer to unused portion of zSql */
>     );
>     int sqlite3_prepare16_v2(
>       sqlite3 *db,            /* Database handle */
>       const void *zSql,       /* SQL statement, UTF-16 encoded */
>       int nByte,              /* Maximum length of zSql in bytes. */
>       sqlite3_stmt **ppStmt,  /* OUT: Statement handle */
>       const void **pzTail     /* OUT: Pointer to unused portion of zSql */
>     );

To execute an SQL query, it must first be compiled into a byte-code program using one of these routines.

The first argument "db" is an database connection obtained from a prior call to sqlite3_open(), sqlite3_open_v2() or sqlite3_open16(). The second argument "zSql" is the statement to be compiled, encoded as either UTF-8 or UTF-16. The sqlite3_prepare() and sqlite3_prepare_v2() interfaces uses UTF-8 and sqlite3_prepare16() and sqlite3_prepare16_v2() use UTF-16.

If the nByte argument is less than zero, then zSql is read up to the first zero terminator. If nByte is non-negative, then it is the maximum number of bytes read from zSql. When nByte is non-negative, the zSql string ends at either the first '\000' or '\u0000' character or until the nByte-th byte, whichever comes first.

*pzTail is made to point to the first byte past the end of the first SQL statement in zSql. These routines only compiles the first statement in zSql, so *pzTail is left pointing to what remains uncompiled.

*ppStmt is left pointing to a compiled prepared statement that can be executed using sqlite3_step(). Or if there is an error, *ppStmt may be set to NULL. If the input text contains no SQL (if the input is and empty string or a comment) then *ppStmt is set to NULL. The calling procedure is responsible for deleting the compiled SQL statement using sqlite3_finalize() after it has finished with it.

On success, SQLITE_OK is returned. Otherwise an error code is returned.

The sqlite3_prepare_v2() and sqlite3_prepare16_v2() interfaces are recommended for all new programs. The two older interfaces are retained for backwards compatibility, but their use is discouraged. In the "v2" interfaces, the prepared statement that is returned (the sqlite3_stmt object) contains a copy of the original SQL text. This causes the sqlite3_step() interface to behave a differently in two ways:

1. If the database schema changes, instead of returning SQLITE_SCHEMA as it always used to do, sqlite3_step() will automatically recompile the SQL statement and try to run it again. If the schema has changed in a way that makes the statement no longer valid, sqlite3_step() will still return SQLITE_SCHEMA. But unlike the legacy behavior, SQLITE_SCHEMA is now a fatal error. Calling sqlite3_prepare_v2() again will not make the error go away. Note: use sqlite3_errmsg() to find the text of the parsing error that results in an SQLITE_SCHEMA return.

2. When an error occurs, sqlite3_step() will return one of the detailed error codes or extended error codes. The legacy behavior was that sqlite3_step() would only return a generic SQLITE_ERROR result code and you would have to make a second call to sqlite3_reset() in order to find the underlying cause of the problem. With the "v2" prepare interfaces, the underlying reason for the error is returned immediately.

### Invariants:

F13011 | The sqlite3_prepare(db,zSql,...) and sqlite3_prepare_v2(db,zSql,...) interfaces interpret the text in their zSql parameter as UTF-8.
F13012 | The sqlite3_prepare16(db,zSql,...) and sqlite3_prepare16_v2(db,zSql,...) interfaces interpret the text in their zSql parameter as UTF-16 in the native byte order.
F13013 | If the nByte argument to sqlite3_prepare_v2(db,zSql,nByte,...) and its variants is less than zero, then SQL text is read from zSql is read up to the first zero terminator.
F13014 | If the nByte argument to sqlite3_prepare_v2(db,zSql,nByte,...) and its variants is non-negative, then nBytes bytes SQL text is read from zSql.
F13015 | In sqlite3_prepare_v2(db,zSql,N,P,pzTail) and its variants if the zSql input text contains more than one SQL statement and pzTail is not NULL, then *pzTail is made to point to the first byte past the end of the first SQL statement in zSql. (TODO: What does *pzTail point to if there is one statement?)
F13016 | A successful call to sqlite3_prepare_v2(db,zSql,N,ppStmt,...) or one of its variants writes into *ppStmt a pointer to a new prepared statement or a pointer to NULL if zSql contains nothing other than whitespace or comments.
F13019 | The sqlite3_prepare_v2() interface and its variants return SQLITE_OK or an appropriate error code upon failure.

## Tracing And Profiling Functions

>     void *sqlite3_trace(sqlite3*, void(*xTrace)(void*,const char*), void*);
>     void *sqlite3_profile(sqlite3*,
>        void(*xProfile)(void*,const char*,sqlite3_uint64), void*);

These routines register callback functions that can be used for tracing and profiling the execution of SQL statements.

The callback function registered by sqlite3_trace() is invoked at various times when an SQL statement is being run by sqlite3_step(). The callback returns a UTF-8 rendering of the SQL statement text as the statement first begins executing. Additional callbacks occur as each triggersubprogram is entered. The callbacks for triggers contain a UTF-8 SQL comment that identifies the trigger.

The callback function registered by sqlite3_profile() is invoked as each SQL statement finishes. The profile callback contains the original statement text and an estimate of wall-clock time of how long that statement took to run.

The sqlite3_profile() API is currently considered experimental and is subject to change or removal in a future release.

The trigger reporting feature of the trace callback is considered experimental and is subject to change or removal in future releases. Future versions of SQLite might also add new trace callback invocations.

### Invariants:

F12281 | The callback function registered by sqlite3_trace() is whenever an SQL statement first begins to execute and whenever a trigger subprogram first begins to run.
F12282 | Each call to sqlite3_trace() overrides the previously registered trace callback.
F12283 | A NULL trace callback disables tracing.
F12284 | The first argument to the trace callback is a copy of the pointer which was the 3rd argument to sqlite3_trace().
F12285 | The second argument to the trace callback is a zero-terminated UTF8 string containing the original text of the SQL statement as it was passed into sqlite3_prepare_v2() or the equivalent, or an SQL comment indicating the beginning of a trigger subprogram.
F12287 | The callback function registered by sqlite3_profile() is invoked as each SQL statement finishes.
F12288 | The first parameter to the profile callback is a copy of the 3rd parameter to sqlite3_profile().
F12289 | The second parameter to the profile callback is a zero-terminated UTF-8 string that contains the complete text of the SQL statement as it was processed by sqlite3_prepare_v2() or the equivalent.
F12290 | The third parameter to the profile callback is an estimate of the number of nanoseconds of wall-clock time required to run the SQL statement from start to finish.

## Setting The Result Of An SQL Function

>     void sqlite3_result_blob(sqlite3_context*, const void*, int, void(*)(void*));
>     void sqlite3_result_double(sqlite3_context*, double);
>     void sqlite3_result_error(sqlite3_context*, const char*, int);
>     void sqlite3_result_error16(sqlite3_context*, const void*, int);
>     void sqlite3_result_error_toobig(sqlite3_context*);
>     void sqlite3_result_error_nomem(sqlite3_context*);
>     void sqlite3_result_error_code(sqlite3_context*, int);
>     void sqlite3_result_int(sqlite3_context*, int);
>     void sqlite3_result_int64(sqlite3_context*, sqlite3_int64);
>     void sqlite3_result_null(sqlite3_context*);
>     void sqlite3_result_text(sqlite3_context*, const char*, int, void(*)(void*));
>     void sqlite3_result_text16(sqlite3_context*, const void*, int, void(*)(void*));
>     void sqlite3_result_text16le(sqlite3_context*, const void*, int,void(*)(void*));
>     void sqlite3_result_text16be(sqlite3_context*, const void*, int,void(*)(void*));
>     void sqlite3_result_value(sqlite3_context*, sqlite3_value*);
>     void sqlite3_result_zeroblob(sqlite3_context*, int n);

These routines are used by the xFunc or xFinal callbacks that implement SQL functions and aggregates. See sqlite3_create_function() and sqlite3_create_function16() for additional information.

These functions work very much like the sqlite3_bind_* family of functions used to bind values to host parameters in prepared statements. Refer to the sqlite3_bind_* documentation for additional information.

The sqlite3_result_blob() interface sets the result from an application defined function to be the BLOB whose content is pointed to by the second parameter and which is N bytes long where N is the third parameter. The sqlite3_result_zeroblob() inerfaces set the result of the application defined function to be a BLOB containing all zero bytes and N bytes in size, where N is the value of the 2nd parameter.

The sqlite3_result_double() interface sets the result from an application defined function to be a floating point value specified by its 2nd argument.

The sqlite3_result_error() and sqlite3_result_error16() functions cause the implemented SQL function to throw an exception. SQLite uses the string pointed to by the 2nd parameter of sqlite3_result_error() or sqlite3_result_error16() as the text of an error message. SQLite interprets the error message string from sqlite3_result_error() as UTF8. SQLite interprets the string from sqlite3_result_error16() as UTF16 in native byte order. If the third parameter to sqlite3_result_error() or sqlite3_result_error16() is negative then SQLite takes as the error message all text up through the first zero character. If the third parameter to sqlite3_result_error() or sqlite3_result_error16() is non-negative then SQLite takes that many bytes (not characters) from the 2nd parameter as the error message. The sqlite3_result_error() and sqlite3_result_error16() routines make a copy private copy of the error message text before they return. Hence, the calling function can deallocate or modify the text after they return without harm. The sqlite3_result_error_code() function changes the error code returned by SQLite as a result of an error in a function. By default, the error code is SQLITE_ERROR.

The sqlite3_result_toobig() interface causes SQLite to throw an error indicating that a string or BLOB is to long to represent. The sqlite3_result_nomem() interface causes SQLite to throw an exception indicating that the a memory allocation failed.

The sqlite3_result_int() interface sets the return value of the application-defined function to be the 32-bit signed integer value given in the 2nd argument. The sqlite3_result_int64() interface sets the return value of the application-defined function to be the 64-bit signed integer value given in the 2nd argument.

The sqlite3_result_null() interface sets the return value of the application-defined function to be NULL.

The sqlite3_result_text(), sqlite3_result_text16(), sqlite3_result_text16le(), and sqlite3_result_text16be() interfaces set the return value of the application-defined function to be a text string which is represented as UTF-8, UTF-16 native byte order, UTF-16 little endian, or UTF-16 big endian, respectively. SQLite takes the text result from the application from the 2nd parameter of the sqlite3_result_text* interfaces. If the 3rd parameter to the sqlite3_result_text* interfaces is negative, then SQLite takes result text from the 2nd parameter through the first zero character. If the 3rd parameter to the sqlite3_result_text* interfaces is non-negative, then as many bytes (not characters) of the text pointed to by the 2nd parameter are taken as the application-defined function result. If the 4th parameter to the sqlite3_result_text* interfaces or sqlite3_result_blob is a non-NULL pointer, then SQLite calls that function as the destructor on the text or blob result when it has finished using that result. If the 4th parameter to the sqlite3_result_text* interfaces or sqlite3_result_blob is the special constant SQLITE_STATIC, then SQLite assumes that the text or blob result is constant space and does not copy the space or call a destructor when it has finished using that result. If the 4th parameter to the sqlite3_result_text* interfaces or sqlite3_result_blob is the special constant SQLITE_TRANSIENT then SQLite makes a copy of the result into space obtained from from sqlite3_malloc() before it returns.

The sqlite3_result_value() interface sets the result of the application-defined function to be a copy the sqlite3_value object specified by the 2nd parameter. The sqlite3_result_value() interface makes a copy of the sqlite3_value so that sqlite3_value specified in the parameter may change or be deallocated after sqlite3_result_value() returns without harm.

These routines are called from within the different thread than the one containing the application-defined function that recieved the sqlite3_context pointer, the results are undefined.

## Obtaining SQL Function Parameter Values

>     const void *sqlite3_value_blob(sqlite3_value*);
>     int sqlite3_value_bytes(sqlite3_value*);
>     int sqlite3_value_bytes16(sqlite3_value*);
>     double sqlite3_value_double(sqlite3_value*);
>     int sqlite3_value_int(sqlite3_value*);
>     sqlite3_int64 sqlite3_value_int64(sqlite3_value*);
>     const unsigned char *sqlite3_value_text(sqlite3_value*);
>     const void *sqlite3_value_text16(sqlite3_value*);
>     const void *sqlite3_value_text16le(sqlite3_value*);
>     const void *sqlite3_value_text16be(sqlite3_value*);
>     int sqlite3_value_type(sqlite3_value*);
>     int sqlite3_value_numeric_type(sqlite3_value*);

The C-language implementation of SQL functions and aggregates uses this set of interface routines to access the parameter values on the function or aggregate.

The xFunc (for scalar functions) or xStep (for aggregates) parameters to sqlite3_create_function() and sqlite3_create_function16() define callbacks that implement the SQL functions and aggregates. The 4th parameter to these callbacks is an array of pointers to sqlite3_value objects. There is one sqlite3_value object for each parameter to the SQL function. These routines are used to extract values from the sqlite3_value objects.

These routines work just like the corresponding sqlite3_column_* routines except that these routines take a single sqlite3_value* pointer instead of an sqlite3_stmt* pointer and an integer column number.

The sqlite3_value_text16() interface extracts a UTF16 string in the native byte-order of the host machine. The sqlite3_value_text16be() and sqlite3_value_text16le() interfaces extract UTF16 strings as big-endian and little-endian respectively.

The sqlite3_value_numeric_type() interface attempts to apply numeric affinity to the value. This means that an attempt is made to convert the value to an integer or floating point. If such a conversion is possible without loss of information (in other words if the value is a string that looks like a number) then the conversion is done. Otherwise no conversion occurs. The datatype after conversion is returned.

Please pay particular attention to the fact that the pointer that is returned from sqlite3_value_blob(), sqlite3_value_text(), or sqlite3_value_text16() can be invalidated by a subsequent call to sqlite3_value_bytes(), sqlite3_value_bytes16(), sqlite3_value_text(), or sqlite3_value_text16().

These routines must be called from the same thread as the SQL function that supplied the sqlite3_value* parameters. Or, if the sqlite3_value* argument comes from the sqlite3_column_value() interface, then these routines should be called from the same thread that ran sqlite3_column_value().

## Virtual File System Objects

>     sqlite3_vfs *sqlite3_vfs_find(const char *zVfsName);
>     int sqlite3_vfs_register(sqlite3_vfs*, int makeDflt);
>     int sqlite3_vfs_unregister(sqlite3_vfs*);

A virtual filesystem (VFS) is an sqlite3_vfs object that SQLite uses to interact with the underlying operating system. Most builds come with a single default VFS that is appropriate for the host computer. New VFSes can be registered and existing VFSes can be unregistered. The following interfaces are provided.

The sqlite3_vfs_find() interface returns a pointer to a VFS given its name. Names are case sensitive. Names are zero-terminated UTF-8 strings. If there is no match, a NULL pointer is returned. If zVfsName is NULL then the default VFS is returned.

New VFSes are registered with sqlite3_vfs_register(). Each new VFS becomes the default VFS if the makeDflt flag is set. The same VFS can be registered multiple times without injury. To make an existing VFS into the default VFS, register it again with the makeDflt flag set. If two different VFSes with the same name are registered, the behavior is undefined. If a VFS is registered with a name that is NULL or an empty string, then the behavior is undefined.

Unregister a VFS with the sqlite3_vfs_unregister() interface. If the default VFS is unregistered, another VFS is chosen as the default. The choice for the new VFS is arbitrary.

## Create Or Redefine SQL Functions

>     int sqlite3_create_function(
>       sqlite3 *db,
>       const char *zFunctionName,
>       int nArg,
>       int eTextRep,
>       void *pApp,
>       void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
>       void (*xStep)(sqlite3_context*,int,sqlite3_value**),
>       void (*xFinal)(sqlite3_context*)
>     );
>     int sqlite3_create_function16(
>       sqlite3 *db,
>       const void *zFunctionName,
>       int nArg,
>       int eTextRep,
>       void *pApp,
>       void (*xFunc)(sqlite3_context*,int,sqlite3_value**),
>       void (*xStep)(sqlite3_context*,int,sqlite3_value**),
>       void (*xFinal)(sqlite3_context*)
>     );

These two functions (collectively known as "function creation routines") are used to add SQL functions or aggregates or to redefine the behavior of existing SQL functions or aggregates. The difference only between the two is that the second parameter, the name of the (scalar) function or aggregate, is encoded in UTF-8 for sqlite3_create_function() and UTF-16 for sqlite3_create_function16().

The first argument is the database connection that holds the SQL function or aggregate is to be added or redefined. If a single program uses more than one database handle internally, then SQL functions or aggregates must be added individually to each database handle with which they will be used.

The second parameter is the name of the SQL function to be created or redefined. The length of the name is limited to 255 bytes, exclusive of the zero-terminator. Note that the name length limit is in bytes, not characters. Any attempt to create a function with a longer name will result in an SQLITE_ERROR error.

The third parameter is the number of arguments that the SQL function or aggregate takes. If this parameter is negative, then the SQL function or aggregate may take any number of arguments.

The fourth parameter, eTextRep, specifies what text encoding this SQL function prefers for its parameters. Any SQL function implementation should be able to work work with UTF-8, UTF-16le, or UTF-16be. But some implementations may be more efficient with one encoding than another. It is allowed to invoke sqlite3_create_function() or sqlite3_create_function16() multiple times with the same function but with different values of eTextRep. When multiple implementations of the same function are available, SQLite will pick the one that involves the least amount of data conversion. If there is only a single implementation which does not care what text encoding is used, then the fourth argument should be SQLITE_ANY.

The fifth parameter is an arbitrary pointer. The implementation of the function can gain access to this pointer using sqlite3_user_data().

The seventh, eighth and ninth parameters, xFunc, xStep and xFinal, are pointers to C-language functions that implement the SQL function or aggregate. A scalar SQL function requires an implementation of the xFunc callback only, NULL pointers should be passed as the xStep and xFinal parameters. An aggregate SQL function requires an implementation of xStep and xFinal and NULL should be passed for xFunc. To delete an existing SQL function or aggregate, pass NULL for all three function callback.

It is permitted to register multiple implementations of the same functions with the same name but with either differing numbers of arguments or differing perferred text encodings. SQLite will use the implementation most closely matches the way in which the SQL function is used.

### Invariants:

F16103 | The sqlite3_create_function16() interface behaves exactly like sqlite3_create_function() in every way except that it interprets the zFunctionName argument as zero-terminated UTF-16 native byte order instead of as a zero-terminated UTF-8.

This page last modified 2008/01/31 20:37:13 UTC