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# System configuration

When NumPy is built, information about system configuration is recorded, and is made available for extension modules using Numpy’s C API. These are mostly defined in `numpyconfig.h` (included in `ndarrayobject.h`). The public symbols are prefixed by `NPY_*`. Numpy also offers some functions for querying information about the platform in use.

For private use, Numpy also constructs a `config.h` in the NumPy include directory, which is not exported by Numpy (that is a python extension which use the numpy C API will not see those symbols), to avoid namespace pollution.

## Data type sizes

The `NPY_SIZEOF_{CTYPE}` constants are defined so that sizeof information is available to the pre-processor.

`NPY_SIZEOF_SHORT`

`NPY_SIZEOF_INT`

`NPY_SIZEOF_LONG`

`NPY_SIZEOF_LONG_LONG`

`NPY_SIZEOF_PY_LONG_LONG`

`NPY_SIZEOF_FLOAT`

`NPY_SIZEOF_DOUBLE`

`NPY_SIZEOF_LONG_DOUBLE`

`NPY_SIZEOF_PY_INTPTR_T`

  Size of a pointer on this platform (sizeof(void *)) (A macro defines NPY_SIZEOF_INTP as well.)

## Platform information

`NPY_CPU_X86`

`NPY_CPU_AMD64`

`NPY_CPU_IA64`

`NPY_CPU_PPC`

`NPY_CPU_PPC64`

`NPY_CPU_SPARC`

`NPY_CPU_SPARC64`

`NPY_CPU_S390`

`NPY_CPU_PARISC`

  New in version 1.3.0.

  CPU architecture of the platform; only one of the above is defined.

  Defined in `numpy/npy_cpu.h`

`NPY_LITTLE_ENDIAN`

`NPY_BIG_ENDIAN`

`NPY_BYTE_ORDER`

  New in version 1.3.0.

  Portable alternatives to the `endian.h` macros of GNU Libc. If big endian, `NPY_BYTE_ORDER` == `NPY_BIG_ENDIAN`, and similarly for little endian architectures.

  Defined in `numpy/npy_endian.h`.

`PyArray_GetEndianness`()

  New in version 1.3.0.

  Returns the endianness of the current platform. One of `NPY_CPU_BIG`, `NPY_CPU_LITTLE`, or `NPY_CPU_UNKNOWN_ENDIAN`.

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