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>.0Type 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>_CODEHolds 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_ONLYSupport only compiler-builtin types. If not given, the macro checks for headers
<sys/types.h>,<stdint.h>, and<stddef.h>, and saves results inHAVE_SYS_TYPES_H,HAVE_STDINT_H, andHAVE_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 areCandCXX. If not specified, it defaults toC.
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_FLAGSString 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_DEFINITIONSA ;-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_INCLUDESA ;-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_OPTIONSAdded in version 3.14.
A ;-list of options to add to the link command (see
try_compile()for further details).
CMAKE_REQUIRED_LIBRARIESA ;-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_DIRECTORIESAdded in version 3.31.
A ;-list of libraries search paths to pass to the linker (see
try_compile()for further details).
CMAKE_REQUIRED_QUIETAdded 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_FILESlist 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