CMAKE_<LANG>_BYTE_ORDER

.. versionadded:: 3.20

Byte order of <LANG> compiler target architecture, if known. If defined and not empty, the value is one of:

BIG_ENDIAN The target architecture is Big Endian.

LITTLE_ENDIAN The target architecture is Little Endian.

This is defined for languages C, CXX, OBJC, OBJCXX, and CUDA.

If :variable:CMAKE_OSX_ARCHITECTURES specifies multiple architectures, the value of CMAKE_<LANG>_BYTE_ORDER is non-empty only if all architectures share the same byte order.

Examples ^^^^^^^^

Example: Checking Endianness """"""""""""""""""""""""""""

Checking endianness (byte order) of the target architecture in a CMake project, where C language is one of the enabled languages, and storing the result in a variable WORDS_BIGENDIAN:

.. code-block:: cmake

if(CMAKE_C_BYTE_ORDER STREQUAL "BIG_ENDIAN") set(WORDS_BIGENDIAN TRUE) elseif(CMAKE_C_BYTE_ORDER STREQUAL "LITTLE_ENDIAN") set(WORDS_BIGENDIAN FALSE) else() set(WORDS_BIGENDIAN FALSE) message(WARNING "Endianness could not be determined.") endif()

Or, if the project doesn't have C language enabled, it can be replaced with some other enabled language. For example, if CXX is enabled:

.. code-block:: cmake

if(CMAKE_CXX_BYTE_ORDER STREQUAL "BIG_ENDIAN") set(WORDS_BIGENDIAN TRUE) elseif(CMAKE_CXX_BYTE_ORDER STREQUAL "LITTLE_ENDIAN") set(WORDS_BIGENDIAN FALSE) else() set(WORDS_BIGENDIAN FALSE) message(WARNING "Endianness could not be determined.") endif()

Note, that in most cases this can be simplified by only checking for a big-endian target:

.. code-block:: cmake

if(CMAKE_C_BYTE_ORDER STREQUAL "BIG_ENDIAN") set(WORDS_BIGENDIAN TRUE) else() set(WORDS_BIGENDIAN FALSE) endif()

Example: Per-language Endianness Check """"""""""""""""""""""""""""""""""""""

Most of the time, architectures used today are consistent in endianness across compilers. But here's when per-language endianness check can matter:

Cross-compilation to different architectures (e.g., big-endian embedded system).
Heterogeneous toolchains where one target architecture is for C language and another target is for different language.
Static libraries or binaries reused across platforms (e.g., distributing precompiled CUDA kernels).

.. code-block:: cmake

if(CMAKE_C_BYTE_ORDER) message(STATUS "C byte order: ${CMAKE_C_BYTE_ORDER}") endif()

if(CMAKE_CXX_BYTE_ORDER) message(STATUS "C++ byte order: ${CMAKE_CXX_BYTE_ORDER}") endif()

if(CMAKE_CUDA_BYTE_ORDER) message(STATUS "CUDA byte order: ${CMAKE_CUDA_BYTE_ORDER}") endif()