CMake/Modules/CheckVariableExists.cmake

#
# Check if the variable exists.
# # CHECK_VARIABLE_EXISTS - macro which checks if the variable exists
# VAR - the name of the variable
# VARIABLE - variable to store the result
#

MACRO(CHECK_VARIABLE_EXISTS VAR VARIABLE)
  IF("${VARIABLE}" MATCHES "^${VARIABLE}$")
    SET(MACRO_CHECK_VARIABLE_DEFINITIONS -DCHECK_VARIABLE_EXISTS=${VAR} 
        ${CMAKE_REQUIRED_FLAGS})
    MESSAGE(STATUS "Looking for ${VARIABLE}")
    IF(CMAKE_REQUIRED_LIBRARIES)
      SET(CHECK_VARIABLE_EXISTS_ADD_LIBRARIES 
          "-DLINK_LIBRARIES:STRING=${CMAKE_REQUIRED_LIBRARIES}")
    ENDIF(CMAKE_REQUIRED_LIBRARIES)
    TRY_COMPILE(${VARIABLE}
               ${CMAKE_BINARY_DIR}
               ${CMAKE_ROOT}/Modules/CheckVariableExists.c
               CMAKE_FLAGS -DCOMPILE_DEFINITIONS:STRING=${MACRO_CHECK_VARIABLE_DEFINITIONS}
                        "${CHECK_VARIABLE_EXISTS_ADD_LIBRARIES}"
               OUTPUT_VARIABLE OUTPUT)
    IF(${VARIABLE})
      SET(${VARIABLE} 1 CACHE INTERNAL "Have variable ${VAR}")
      MESSAGE(STATUS "Looking for ${VARIABLE} - found")
    ELSE(${VARIABLE})
      SET(${VARIABLE} "" CACHE INTERNAL "Have variable ${VAR}")
      MESSAGE(STATUS "Looking for ${VARIABLE} - not found")
      WRITE_FILE(${CMAKE_BINARY_DIR}/CMakeError.log 
        "Determining if the variable ${VAR} exists failed with the following output:\n"
        "${OUTPUT}\n" APPEND)
    ENDIF(${VARIABLE})
  ENDIF("${VARIABLE}" MATCHES "^${VARIABLE}$")
ENDMACRO(CHECK_VARIABLE_EXISTS)