macro(determine_gflags_namespace VARIABLE)

  if (NOT DEFINED "${VARIABLE}")

    if (CMAKE_REQUIRED_INCLUDES)

      set (CHECK_INCLUDE_FILE_CXX_INCLUDE_DIRS "-DINCLUDE_DIRECTORIES=${CMAKE_REQUIRED_INCLUDES}")

    else ()

      set (CHECK_INCLUDE_FILE_CXX_INCLUDE_DIRS)

    endif ()

    set(MACRO_CHECK_INCLUDE_FILE_FLAGS ${CMAKE_REQUIRED_FLAGS})

    set(_NAMESPACES gflags google)

    set(_check_code

"

#include <gflags/gflags.h>

int main(int argc, char**argv)

{

  GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);

}

")

    if (NOT CMAKE_REQUIRED_QUIET)

      message (STATUS "Looking for gflags namespace")

    endif ()

    if (${ARGC} EQUAL 3)

      set (CMAKE_CXX_FLAGS_SAVE ${CMAKE_CXX_FLAGS})

      set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${ARGV2}")

    endif ()

    set (_check_file

        ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/DetermineGflagsNamespace.cxx)

    foreach (_namespace ${_NAMESPACES})

      file (WRITE "${_check_file}" "${_check_code}")

      try_compile (${VARIABLE}

        "${CMAKE_BINARY_DIR}" "${_check_file}"

        COMPILE_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS}" -DGFLAGS_NAMESPACE=${_namespace}

        LINK_LIBRARIES "${gflags_LIBRARIES}"

        CMAKE_FLAGS -DINCLUDE_DIRECTORIES:STRING="${gflags_INCLUDE_DIR}"

        OUTPUT_VARIABLE OUTPUT)

      if (${VARIABLE})

        set (${VARIABLE} ${_namespace} CACHE INTERNAL "gflags namespace" FORCE)

        break ()

      else ()

        file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log

          "Determining the gflags namespace ${_namespace} failed with the following output:\n"

          "${OUTPUT}\n\n")

      endif ()

    endforeach (_namespace)

    if (${ARGC} EQUAL 3)

      set (CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS_SAVE})

    endif ()

    if (${VARIABLE})

      if (NOT CMAKE_REQUIRED_QUIET)

        message (STATUS "Looking for gflags namespace - ${${VARIABLE}}")

      endif ()

      file (APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log

        "Determining the gflags namespace passed with the following output:\n"

        "${OUTPUT}\n\n")

    else ()

      if (NOT CMAKE_REQUIRED_QUIET)

        message (STATUS "Looking for gflags namespace - failed")

      endif ()

      set (${VARIABLE} ${_namespace} CACHE INTERNAL "gflags namespace")

    endif ()

  endif ()

endmacro ()