# CheckPrototypeDefinition

Check if a `C` function has the expected prototype.

check_prototype_definition

      check_prototype_definition(<function> <prototype> <return> <headers> <variable>)

  `<function>`

    The name of the function whose prototype is being checked.

  `<prototype>`

    The expected prototype of the function, provided as a string.

  `<return>`

    The return value of the function. This will be used as a return value in the function definition body of the generated test program to verify that the function's return type matches the expected type.

  `<headers>`

    A semicolon-separated list of header file names required for checking the function prototype.

  `<variable>`

    The name of the variable to store the check result. This variable will be created as an internal cache variable.

  This command generates a test program and verifies that it builds without errors. The generated test program includes specified `<headers>`, defines a function with given literal `<prototype>` and `<return>` value and then uses the specified `<function>`. The simplified test program can be illustrated as:

      #include <headers>
      // ...
      <prototype> { return <return>; }
      int main(...) { ...<function>()... }

The following variables may be set before calling this function 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>_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_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.

## Examples

Checking if the `getpwent_r()` function on Solaris/illumos systems has the expected prototype:

    include(CheckPrototypeDefinition)

    check_prototype_definition(
      getpwent_r
      "struct passwd *getpwent_r(struct passwd *src, char *buf, int buflen)"
      "NULL"
      "unistd.h;pwd.h"
      HAVE_SOLARIS_GETPWENT_R
    )