1# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
2# file Copyright.txt or https://cmake.org/licensing for details.
3
4#[=======================================================================[.rst:
5CheckFunctionExists
6-------------------
7
8Check if a C function can be linked
9
10.. command:: check_function_exists
11
12  .. code-block:: cmake
13
14    check_function_exists(<function> <variable>)
15
16  Checks that the ``<function>`` is provided by libraries on the system and store
17  the result in a ``<variable>``, which will be created as an internal
18  cache variable.
19
20The following variables may be set before calling this macro to modify the
21way the check is run:
22
23``CMAKE_REQUIRED_FLAGS``
24  string of compile command line flags.
25``CMAKE_REQUIRED_DEFINITIONS``
26  a :ref:`;-list <CMake Language Lists>` of macros to define (-DFOO=bar).
27``CMAKE_REQUIRED_INCLUDES``
28  a :ref:`;-list <CMake Language Lists>` of header search paths to pass to
29  the compiler.
30``CMAKE_REQUIRED_LINK_OPTIONS``
31  .. versionadded:: 3.14
32    a :ref:`;-list <CMake Language Lists>` of options to add to the link command.
33``CMAKE_REQUIRED_LIBRARIES``
34  a :ref:`;-list <CMake Language Lists>` of libraries to add to the link
35  command. See policy :policy:`CMP0075`.
36``CMAKE_REQUIRED_QUIET``
37  .. versionadded:: 3.1
38    execute quietly without messages.
39
40.. note::
41
42  Prefer using :Module:`CheckSymbolExists` instead of this module,
43  for the following reasons:
44
45  * ``check_function_exists()`` can't detect functions that are inlined
46    in headers or specified as a macro.
47
48  * ``check_function_exists()`` can't detect anything in the 32-bit
49    versions of the Win32 API, because of a mismatch in calling conventions.
50
51  * ``check_function_exists()`` only verifies linking, it does not verify
52    that the function is declared in system headers.
53#]=======================================================================]
54
55include_guard(GLOBAL)
56
57macro(CHECK_FUNCTION_EXISTS FUNCTION VARIABLE)
58  if(NOT DEFINED "${VARIABLE}" OR "x${${VARIABLE}}" STREQUAL "x${VARIABLE}")
59    set(MACRO_CHECK_FUNCTION_DEFINITIONS
60      "-DCHECK_FUNCTION_EXISTS=${FUNCTION} ${CMAKE_REQUIRED_FLAGS}")
61    if(NOT CMAKE_REQUIRED_QUIET)
62      message(CHECK_START "Looking for ${FUNCTION}")
63    endif()
64    if(CMAKE_REQUIRED_LINK_OPTIONS)
65      set(CHECK_FUNCTION_EXISTS_ADD_LINK_OPTIONS
66        LINK_OPTIONS ${CMAKE_REQUIRED_LINK_OPTIONS})
67    else()
68      set(CHECK_FUNCTION_EXISTS_ADD_LINK_OPTIONS)
69    endif()
70    if(CMAKE_REQUIRED_LIBRARIES)
71      set(CHECK_FUNCTION_EXISTS_ADD_LIBRARIES
72        LINK_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
73    else()
74      set(CHECK_FUNCTION_EXISTS_ADD_LIBRARIES)
75    endif()
76    if(CMAKE_REQUIRED_INCLUDES)
77      set(CHECK_FUNCTION_EXISTS_ADD_INCLUDES
78        "-DINCLUDE_DIRECTORIES:STRING=${CMAKE_REQUIRED_INCLUDES}")
79    else()
80      set(CHECK_FUNCTION_EXISTS_ADD_INCLUDES)
81    endif()
82
83    if(CMAKE_C_COMPILER_LOADED)
84      set(_cfe_source ${CMAKE_ROOT}/Modules/CheckFunctionExists.c)
85    elseif(CMAKE_CXX_COMPILER_LOADED)
86      set(_cfe_source ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CheckFunctionExists/CheckFunctionExists.cxx)
87      configure_file(${CMAKE_ROOT}/Modules/CheckFunctionExists.c "${_cfe_source}" COPYONLY)
88    else()
89      message(FATAL_ERROR "CHECK_FUNCTION_EXISTS needs either C or CXX language enabled")
90    endif()
91
92    try_compile(${VARIABLE}
93      ${CMAKE_BINARY_DIR}
94      ${_cfe_source}
95      COMPILE_DEFINITIONS ${CMAKE_REQUIRED_DEFINITIONS}
96      ${CHECK_FUNCTION_EXISTS_ADD_LINK_OPTIONS}
97      ${CHECK_FUNCTION_EXISTS_ADD_LIBRARIES}
98      CMAKE_FLAGS -DCOMPILE_DEFINITIONS:STRING=${MACRO_CHECK_FUNCTION_DEFINITIONS}
99      "${CHECK_FUNCTION_EXISTS_ADD_INCLUDES}"
100      OUTPUT_VARIABLE OUTPUT)
101    unset(_cfe_source)
102
103    if(${VARIABLE})
104      set(${VARIABLE} 1 CACHE INTERNAL "Have function ${FUNCTION}")
105      if(NOT CMAKE_REQUIRED_QUIET)
106        message(CHECK_PASS "found")
107      endif()
108      file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
109        "Determining if the function ${FUNCTION} exists passed with the following output:\n"
110        "${OUTPUT}\n\n")
111    else()
112      if(NOT CMAKE_REQUIRED_QUIET)
113        message(CHECK_FAIL "not found")
114      endif()
115      set(${VARIABLE} "" CACHE INTERNAL "Have function ${FUNCTION}")
116      file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
117        "Determining if the function ${FUNCTION} exists failed with the following output:\n"
118        "${OUTPUT}\n\n")
119    endif()
120  endif()
121endmacro()
122