Fix CMake CXX_STANDARD handling

https://sigrok.org/gitweb/?p=pulseview.git;a=commit;f=CMakeLists.txt;h=fa8d0fcb4cff4f19943fe3ff152dc1428b400b01 introduced a CXX_STANDARD value of 17 while still only requiring cmake 2.8.12.

However, https://cmake.org/cmake/help/latest/prop_tgt/CXX_STANDARD.html#cxx-standard shows that a value of 17 was introduced with cmake 3.8, leading to

"CXX_STANDARD is set to invalid value '17'" when trying to build with cmake < 3.8.

Hence, for versions below 3.8, we only check for up to 14.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 395222a25a7838a1717eb0c4427850d32696ebaa..c206d9158dc0994761ea88538c39670934fab1ec 100644 (file)
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -83,23 +83,39 @@ include(memaccess)
 
 find_package(PkgConfig)
 
-check_cxx_compiler_flag("-std=c++17" HAVE_STD_CXX_17)
-check_cxx_compiler_flag("-std=c++14" HAVE_STD_CXX_14)
-check_cxx_compiler_flag("-std=c++11" HAVE_STD_CXX_11)
-if(HAVE_STD_CXX_17)
-       message(STATUS "Using C++17 for the application build")
-       set(CMAKE_CXX_STANDARD 17)
-       set(REQUIRED_STD_CXX_FLAGS "-std=c++17")
-elseif(HAVE_STD_CXX_14)
-       message(STATUS "Using C++14 for the application build")
-       set(CMAKE_CXX_STANDARD 14)
-       set(REQUIRED_STD_CXX_FLAGS "-std=c++14")
-elseif(HAVE_STD_CXX_11)
-       message(STATUS "Using C++11 for the application build")
-       set(CMAKE_CXX_STANDARD 11)
-       set(REQUIRED_STD_CXX_FLAGS "-std=c++11")
+if(${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.8.0")
+       check_cxx_compiler_flag("-std=c++17" HAVE_STD_CXX_17)
+       check_cxx_compiler_flag("-std=c++14" HAVE_STD_CXX_14)
+       check_cxx_compiler_flag("-std=c++11" HAVE_STD_CXX_11)
+       if(HAVE_STD_CXX_17)
+               message(STATUS "Using C++17 for the application build")
+               set(CMAKE_CXX_STANDARD 17)
+               set(REQUIRED_STD_CXX_FLAGS "-std=c++17")
+       elseif(HAVE_STD_CXX_14)
+               message(STATUS "Using C++14 for the application build")
+               set(CMAKE_CXX_STANDARD 14)
+               set(REQUIRED_STD_CXX_FLAGS "-std=c++14")
+       elseif(HAVE_STD_CXX_11)
+               message(STATUS "Using C++11 for the application build")
+               set(CMAKE_CXX_STANDARD 11)
+               set(REQUIRED_STD_CXX_FLAGS "-std=c++11")
+       else()
+               message(FATAL_ERROR "Need modern C++, at least language standard 11")
+       endif()
 else()
-       message(FATAL_ERROR "Need modern C++, at least language standard 11")
+       check_cxx_compiler_flag("-std=c++14" HAVE_STD_CXX_14)
+       check_cxx_compiler_flag("-std=c++11" HAVE_STD_CXX_11)
+       if(HAVE_STD_CXX_14)
+               message(STATUS "Using C++14 for the application build")
+               set(CMAKE_CXX_STANDARD 14)
+               set(REQUIRED_STD_CXX_FLAGS "-std=c++14")
+       elseif(HAVE_STD_CXX_11)
+               message(STATUS "Using C++11 for the application build")
+               set(CMAKE_CXX_STANDARD 11)
+               set(REQUIRED_STD_CXX_FLAGS "-std=c++11")
+       else()
+               message(FATAL_ERROR "Need modern C++, at least language standard 11")
+       endif()
 endif()
 
 list(APPEND PKGDEPS glib-2.0>=2.28.0)