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CheckTypeSize: Modernize and clarify documentation

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Spell out the list of result variables as a definition list rather
than in prose.

Fixes: #23247
This commit is contained in:
Brad King
2022-02-18 11:33:06 -05:00
parent a1cb448580
commit 65e4d29e35
1 changed files with 36 additions and 29 deletions
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65
Modules/CheckTypeSize.cmake
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@@ -7,46 +7,53 @@ CheckTypeSize
Check sizeof a type
.. command:: CHECK_TYPE_SIZE
.. command:: check_type_size
.. code-block:: cmake
CHECK_TYPE_SIZE(TYPE VARIABLE [BUILTIN_TYPES_ONLY]
[LANGUAGE <language>])
check_type_size(<type> <variable> [BUILTIN_TYPES_ONLY]
[LANGUAGE <language>])
Check if the type exists and determine its size. On return,
``HAVE_${VARIABLE}`` holds the existence of the type, and ``${VARIABLE}``
holds one of the following:
Check if the type exists and determine its size. Results are reported
in the following variables:
::
``HAVE_<variable>``
Holds a true or false value indicating whether the type exists.
<size> = type has non-zero size <size>
"0" = type has arch-dependent size (see below)
"" = type does not exist
``<variable>``
Holds one of the following values:
Both ``HAVE_${VARIABLE}`` and ``${VARIABLE}`` will be created as internal
cache variables.
``<size>``
Type has non-zero size ``<size>``.
Furthermore, the variable ``${VARIABLE}_CODE`` holds C preprocessor code
to define the macro ``${VARIABLE}`` to the size of the type, or leave
the macro undefined if the type does not exist.
``0``
Type has architecture-dependent size. This may occur when
:variable:`CMAKE_OSX_ARCHITECTURES` has multiple architectures.
In this case ``<variable>_CODE`` contains C preprocessor tests
mapping from each architecture macro to the corresponding type size.
The list of architecture macros is stored in ``<variable>_KEYS``,
and the value for each key is stored in ``<variable>-<key>``.
The variable ``${VARIABLE}`` may be ``0`` when
:variable:`CMAKE_OSX_ARCHITECTURES` has multiple architectures for building
OS X universal binaries. This indicates that the type size varies across
architectures. In this case ``${VARIABLE}_CODE`` contains C preprocessor
tests mapping from each architecture macro to the corresponding type size.
The list of architecture macros is stored in ``${VARIABLE}_KEYS``, and the
value for each key is stored in ``${VARIABLE}-${KEY}``.
"" (empty string)
Type does not exist.
If the ``BUILTIN_TYPES_ONLY`` option is not given, the macro checks for
headers ``<sys/types.h>``, ``<stdint.h>``, and ``<stddef.h>``, and saves
results in ``HAVE_SYS_TYPES_H``, ``HAVE_STDINT_H``, and ``HAVE_STDDEF_H``.
The type size check automatically includes the available headers, thus
supporting checks of types defined in the headers.
``<variable>_CODE``
Holds C preprocessor code to define the macro ``<variable>`` to the size
of the type, or to leave the macro undefined if the type does not exist.
If ``LANGUAGE`` is set, the specified compiler will be used to perform the
check. Acceptable values are ``C`` and ``CXX``.
The options are:
``BUILTIN_TYPES_ONLY``
Support only compiler-builtin types. If *not* given, the macro checks
for headers ``<sys/types.h>``, ``<stdint.h>``, and ``<stddef.h>``, and
saves results in ``HAVE_SYS_TYPES_H``, ``HAVE_STDINT_H``, and
``HAVE_STDDEF_H``. The type size check automatically includes the
available headers, thus supporting checks of types defined in the headers.
``LANGUAGE <language>``
Use the ``<language>`` compiler to perform the check.
Acceptable values are ``C`` and ``CXX``.
Despite the name of the macro you may use it to check the size of more
complex expressions, too. To check e.g. for the size of a struct