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. Results are reported in the following variables: - HAVE_<variable>
- Holds a true or false value indicating whether the type exists. 
- <variable>
- Holds one of the following values: - <size>
- Type has non-zero size - <size>.
- 0
- Type has architecture-dependent size. This may occur when - CMAKE_OSX_ARCHITECTUREShas multiple architectures. In this case- <variable>_CODEcontains 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. 
 
- <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.
 - 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- Cand- CXX. If not specified, it defaults to- C.
 
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 additional flags to pass to the compiler. The string must be space-delimited--a ;-list will not work. The contents of
CMAKE_<LANG>_FLAGSand its associated configuration-specific variable are automatically added to the compiler command before the contents ofCMAKE_REQUIRED_FLAGS.
CMAKE_REQUIRED_DEFINITIONS
A ;-list of compiler definitions of the form
-DFOOor-DFOO=bar. A definition for the name specified by<resultVar>will also be added automatically.
CMAKE_REQUIRED_INCLUDES
A ;-list of header search paths to pass to the compiler. These will be the only header search paths used--the contents of the
INCLUDE_DIRECTORIESdirectory property will be ignored.
CMAKE_REQUIRED_LINK_OPTIONS
Added in version 3.14.
A ;-list of options to add to the link command (see
try_compile()for further details).
CMAKE_REQUIRED_LIBRARIES
A ;-list of libraries to add to the link command. These can be the name of system libraries or they can be Imported Targets (see
try_compile()for further details).
CMAKE_REQUIRED_LINK_DIRECTORIES
Added in version 3.31.
A ;-list of libraries search paths to pass to the linker (see
try_compile()for further details).
CMAKE_REQUIRED_QUIET
Added in version 3.1.
If this variable evaluates to a boolean true value, all status messages associated with the check will be suppressed.
- CMAKE_EXTRA_INCLUDE_FILES
- list of extra headers to include. 
Examples¶
Consider the code:
include(CheckTypeSize)
# Check for size of long.
check_type_size(long SIZEOF_LONG)
message("HAVE_SIZEOF_LONG: ${HAVE_SIZEOF_LONG}")
message("SIZEOF_LONG: ${SIZEOF_LONG}")
message("SIZEOF_LONG_CODE: ${SIZEOF_LONG_CODE}")
On a 64-bit architecture, the output may look something like this:
HAVE_SIZEOF_LONG: TRUE
SIZEOF_LONG: 8
SIZEOF_LONG_CODE: #define SIZEOF_LONG 8
On Apple platforms, when CMAKE_OSX_ARCHITECTURES has multiple
architectures, types may have architecture-dependent sizes.
For example, with the code
include(CheckTypeSize)
check_type_size(long SIZEOF_LONG)
message("HAVE_SIZEOF_LONG: ${HAVE_SIZEOF_LONG}")
message("SIZEOF_LONG: ${SIZEOF_LONG}")
foreach(key IN LISTS SIZE_OF_LONG_KEYS)
  message("key: ${key}")
  message("value: ${SIZE_OF_LONG-${key}}")
endforeach()
message("SIZEOF_LONG_CODE:
${SIZEOF_LONG_CODE}")
the result may be:
HAVE_SIZEOF_LONG: TRUE
SIZEOF_LONG: 0
key: __i386
value: 4
key: __x86_64
value: 8
SIZEOF_LONG_CODE:
#if defined(__i386)
# define SIZE_OF_LONG 4
#elif defined(__x86_64)
# define SIZE_OF_LONG 8
#else
# error SIZE_OF_LONG unknown
#endif
