# CheckTypeSize

Check sizeof a type

    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:

    <size> = type has non-zero size <size>
    "0"    = type has arch-dependent size (see below)
    ""     = type does not exist

Both `HAVE_${VARIABLE}` and `${VARIABLE}` will be created as internal cache variables.

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.

The variable “${VARIABLE}” may be “0” when CMAKE_OSX_ARCHITECTURES has multiple architectures for building OS X universal binaries. This indicates that the type size varies across architectures. In this case “${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}”.

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.

If LANGUAGE is set, the specified compiler will be used 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 member you can do something like this:

    check_type_size("((struct something*)0)->member" SIZEOF_MEMBER)

The following variables may be set before calling this macro to modify the way the check is run:

    CMAKE_REQUIRED_FLAGS = string of compile command line flags
    CMAKE_REQUIRED_DEFINITIONS = list of macros to define (-DFOO=bar)
    CMAKE_REQUIRED_INCLUDES = list of include directories
    CMAKE_REQUIRED_LIBRARIES = list of libraries to link
    CMAKE_REQUIRED_QUIET = execute quietly without messages
    CMAKE_EXTRA_INCLUDE_FILES = list of extra headers to include