# CheckTypeSize

Check sizeof a type

`CHECK_TYPE_SIZE`

      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_LINK_OPTIONS  = list of options to pass to link command
    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