Fix overridde CMAKE_C_STANDARD, CMAKE_C_STANDARD_REQUIRED, CMAKE_C_EXTENSIONS. False...

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>

diff --git a/CMakeLists.txt b/CMakeLists.txt
index deb075d10691214f1a841e48fd3a54943cb82a65..dca75063a5c07747968b0ccc0ce2588df284c96a 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -9,13 +9,13 @@ message(STATUS "Using CMake version ${CMAKE_VERSION}")
 # If not specified on the command line, enable C11 as the default
 # Configuration items that affect the global compiler environment standards
 # should be issued before the "project" command.
-if(NOT CMAKE_C_STANDARD)
+if(NOT DEFINED CMAKE_C_STANDARD)
     set(CMAKE_C_STANDARD 11)          # The C standard whose features are requested to build this target
 endif()
-if(NOT CMAKE_C_STANDARD_REQUIRED)
+if(NOT DEFINED CMAKE_C_STANDARD_REQUIRED)
     set(CMAKE_C_STANDARD_REQUIRED ON) # Boolean describing whether the value of C_STANDARD is a requirement
 endif()
-if(NOT CMAKE_C_EXTENSIONS)
+if(NOT DEFINED CMAKE_C_EXTENSIONS)
     set(CMAKE_C_EXTENSIONS OFF)       # Boolean specifying whether compiler specific extensions are requested
 endif()
 set(VALID_C_STANDARDS "99" "11")