Check sizeof a type

check_type_size(<type> <variable> [BUILTIN_TYPES_ONLY]
                                  [LANGUAGE <language>])

Check if the type exists and determine its size. Results are reported in the following variables:


Holds a true or false value indicating whether the type exists.


Holds one of the following values:


Type has non-zero size <size>.


Type has architecture-dependent size. This may occur when 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>.

"" (empty string)

Type does not exist.


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.

The options are:


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 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:


string of compile command line flags.


list of macros to define (-DFOO=bar).


list of include directories.


New in version 3.14: list of options to pass to link command.


list of libraries to link.


New in version 3.1: execute quietly without messages.


list of extra headers to include.