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# Distributed under the OSI-approved BSD 3-Clause License. See accompanying
# file LICENSE.rst or https://cmake.org/licensing for details.
#[=======================================================================[.rst:
CheckVariableExists
-------------------
This module provides a command to check whether a C variable exists.
Load this module in a CMake project with:
.. code-block:: cmake
include(CheckVariableExists)
Commands
^^^^^^^^
This module provides the following command:
.. command:: check_variable_exists
Checks once if a C variable exists:
.. code-block:: cmake
check_variable_exists(<var> <variable>)
This command attempts to compile and link a test C program that references
the specified C variable ``<var>``. A boolean result of whether
the check was successful is stored in an internal cache variable
``<variable>``.
.. note::
Prefer using :module:`CheckSymbolExists` or :module:`CheckSourceCompiles`
instead of this command for more robust detection. This command performs
a link-only check and doesn't detect whether a variable is also declared
in system or library headers. Neither can it detect variables that might
be defined as preprocessor macros.
.. rubric:: Variables Affecting the Check
The following variables may be set before calling this command to modify
the way the check is run:
.. include:: /module/include/CMAKE_REQUIRED_FLAGS.rst
.. include:: /module/include/CMAKE_REQUIRED_DEFINITIONS.rst
.. include:: /module/include/CMAKE_REQUIRED_LINK_OPTIONS.rst
.. include:: /module/include/CMAKE_REQUIRED_LIBRARIES.rst
.. include:: /module/include/CMAKE_REQUIRED_LINK_DIRECTORIES.rst
.. include:: /module/include/CMAKE_REQUIRED_QUIET.rst
Examples
^^^^^^^^
Example: Basic Usage
""""""""""""""""""""
In the following example, a check is performed whether the linker sees the
C variable ``tzname`` and stores the check result in the
``PROJECT_HAVE_TZNAME`` internal cache variable:
.. code-block:: cmake
include(CheckVariableExists)
check_variable_exists(tzname PROJECT_HAVE_TZNAME)
Example: Isolated Check With Linked Libraries
"""""""""""""""""""""""""""""""""""""""""""""
In the following example, this module is used in combination with the
:module:`CMakePushCheckState` module to link additional required library
using the ``CMAKE_REQUIRED_LIBRARIES`` variable. For example, in a find
module, to check whether the Net-SNMP library has the
``usmHMAC192SHA256AuthProtocol`` array:
.. code-block:: cmake
include(CheckVariableExists)
include(CMakePushCheckState)
find_library(SNMP_LIBRARY NAMES netsnmp)
if(SNMP_LIBRARY)
cmake_push_check_state(RESET)
set(CMAKE_REQUIRED_LIBRARIES ${SNMP_LIBRARY})
check_variable_exists(usmHMAC192SHA256AuthProtocol SNMP_HAVE_SHA256)
cmake_pop_check_state()
endif()
See Also
^^^^^^^^
* The :module:`CheckSymbolExists` module to check whether a C symbol exists.
#]=======================================================================]
include_guard(GLOBAL)
macro(CHECK_VARIABLE_EXISTS VAR VARIABLE)
if(NOT DEFINED "${VARIABLE}")
set(MACRO_CHECK_VARIABLE_DEFINITIONS
"-DCHECK_VARIABLE_EXISTS=${VAR} ${CMAKE_REQUIRED_FLAGS}")
if(NOT CMAKE_REQUIRED_QUIET)
message(CHECK_START "Looking for ${VAR}")
endif()
if(CMAKE_REQUIRED_LINK_OPTIONS)
set(CHECK_VARIABLE_EXISTS_ADD_LINK_OPTIONS
LINK_OPTIONS ${CMAKE_REQUIRED_LINK_OPTIONS})
else()
set(CHECK_VARIABLE_EXISTS_ADD_LINK_OPTIONS)
endif()
if(CMAKE_REQUIRED_LIBRARIES)
set(CHECK_VARIABLE_EXISTS_ADD_LIBRARIES
LINK_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
else()
set(CHECK_VARIABLE_EXISTS_ADD_LIBRARIES)
endif()
if(CMAKE_REQUIRED_LINK_DIRECTORIES)
set(_CVE_LINK_DIRECTORIES
"-DLINK_DIRECTORIES:STRING=${CMAKE_REQUIRED_LINK_DIRECTORIES}")
else()
set(_CVE_LINK_DIRECTORIES)
endif()
try_compile(${VARIABLE}
SOURCES ${CMAKE_ROOT}/Modules/CheckVariableExists.c
COMPILE_DEFINITIONS ${CMAKE_REQUIRED_DEFINITIONS}
${CHECK_VARIABLE_EXISTS_ADD_LINK_OPTIONS}
${CHECK_VARIABLE_EXISTS_ADD_LIBRARIES}
CMAKE_FLAGS -DCOMPILE_DEFINITIONS:STRING=${MACRO_CHECK_VARIABLE_DEFINITIONS}
"${_CVE_LINK_DIRECTORIES}"
)
unset(_CVE_LINK_DIRECTORIES)
if(${VARIABLE})
set(${VARIABLE} 1 CACHE INTERNAL "Have variable ${VAR}")
if(NOT CMAKE_REQUIRED_QUIET)
message(CHECK_PASS "found")
endif()
else()
set(${VARIABLE} "" CACHE INTERNAL "Have variable ${VAR}")
if(NOT CMAKE_REQUIRED_QUIET)
message(CHECK_FAIL "not found")
endif()
endif()
endif()
endmacro()
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