# CheckCompilerFlag

Added in version 3.19.

Check whether the compiler supports a given flag.

check_compiler_flag

      check_compiler_flag(<lang> <flag> <resultVar>)

Check that the `<flag>` is accepted by the compiler without a diagnostic. Stores the result in an internal cache entry named `<resultVar>`.

A positive result from this check indicates only that the compiler did not issue a diagnostic message when given the flag. Whether the flag has any effect or even a specific one is beyond the scope of this module.

The check is only performed once, with the result cached in the variable named by `<resultVar>`. Every subsequent CMake run will reuse this cached value rather than performing the check again, even if the `<code>` changes. In order to force the check to be re-evaluated, the variable named by `<resultVar>` must be manually removed from the cache.

The compile and link commands can be influenced by setting any of the following variables prior to calling `check_compiler_flag()`

> `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>_FLAGS` and its associated configuration-specific variable are automatically added to the compiler command before the contents of `CMAKE_REQUIRED_FLAGS`.

> `CMAKE_REQUIRED_DEFINITIONS`

>   A ;-list of compiler definitions of the form `-DFOO` or `-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_DIRECTORIES` directory 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_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.