mirror of
https://gitlab.kitware.com/cmake/cmake.git
synced 2026-09-25 04:09:36 +03:00
Peter Kokot
59da6d9e5c
- Fixed typo in the module description. - Added examples section highlighting the code migration towards the `CMAKE_<LANG>_BYTE_ORDER` variable. - Documented command similar to other modules. - Added examples for the `CMAKE_<LANG>_BYTE_ORDER` variable and explained when endianness for different languages can be used.
96 lines
2.6 KiB
ReStructuredText
96 lines
2.6 KiB
ReStructuredText
CMAKE_<LANG>_BYTE_ORDER
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-----------------------
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.. versionadded:: 3.20
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Byte order of ``<LANG>`` compiler target architecture, if known.
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If defined and not empty, the value is one of:
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``BIG_ENDIAN``
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The target architecture is Big Endian.
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``LITTLE_ENDIAN``
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The target architecture is Little Endian.
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This is defined for languages ``C``, ``CXX``, ``OBJC``, ``OBJCXX``,
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and ``CUDA``.
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If :variable:`CMAKE_OSX_ARCHITECTURES` specifies multiple architectures, the
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value of ``CMAKE_<LANG>_BYTE_ORDER`` is non-empty only if all architectures
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share the same byte order.
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Examples
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^^^^^^^^
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Example: Checking Endianness
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""""""""""""""""""""""""""""
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Checking endianness (byte order) of the target architecture in a CMake
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project, where ``C`` language is one of the enabled languages, and storing
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the result in a variable ``WORDS_BIGENDIAN``:
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.. code-block:: cmake
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if(CMAKE_C_BYTE_ORDER STREQUAL "BIG_ENDIAN")
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set(WORDS_BIGENDIAN TRUE)
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elseif(CMAKE_C_BYTE_ORDER STREQUAL "LITTLE_ENDIAN")
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set(WORDS_BIGENDIAN FALSE)
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else()
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set(WORDS_BIGENDIAN FALSE)
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message(WARNING "Endianness could not be determined.")
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endif()
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Or, if the project doesn't have ``C`` language enabled, it can be replaced
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with some other enabled language. For example, if ``CXX`` is enabled:
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.. code-block:: cmake
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if(CMAKE_CXX_BYTE_ORDER STREQUAL "BIG_ENDIAN")
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set(WORDS_BIGENDIAN TRUE)
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elseif(CMAKE_CXX_BYTE_ORDER STREQUAL "LITTLE_ENDIAN")
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set(WORDS_BIGENDIAN FALSE)
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else()
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set(WORDS_BIGENDIAN FALSE)
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message(WARNING "Endianness could not be determined.")
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endif()
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Note, that in most cases this can be simplified by only checking for a
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big-endian target:
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.. code-block:: cmake
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if(CMAKE_C_BYTE_ORDER STREQUAL "BIG_ENDIAN")
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set(WORDS_BIGENDIAN TRUE)
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else()
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set(WORDS_BIGENDIAN FALSE)
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endif()
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Example: Per-language Endianness Check
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""""""""""""""""""""""""""""""""""""""
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Most of the time, architectures used today are consistent in endianness
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across compilers. But here's when per-language endianness check can matter:
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* Cross-compilation to different architectures (e.g., big-endian embedded
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system).
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* Heterogeneous toolchains where one target architecture is for C language
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and another target is for different language.
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* Static libraries or binaries reused across platforms (e.g., distributing
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precompiled CUDA kernels).
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.. code-block:: cmake
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if(CMAKE_C_BYTE_ORDER)
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message(STATUS "C byte order: ${CMAKE_C_BYTE_ORDER}")
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endif()
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if(CMAKE_CXX_BYTE_ORDER)
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message(STATUS "C++ byte order: ${CMAKE_CXX_BYTE_ORDER}")
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endif()
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if(CMAKE_CUDA_BYTE_ORDER)
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message(STATUS "CUDA byte order: ${CMAKE_CUDA_BYTE_ORDER}")
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endif()
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