Tell CMake to use C++ compiler for C files coming from CMake?

Question

This is similar to Force CMake to use C++ compiler for C files with Visual Studio, but its not quite the same. Its not the same because a its CMake file causing the failure;

Answer 1

There are ways to add .c as a valid file extension for the CXX compiler. Even this being very advanced CMake stuff, you may need - if you are bound to support older versions of CMake - a "make rules overwrite script" anyway.

So I've successfully tested the following:

CryptoppMakeRulesOverwrite.cmake

list(APPEND CMAKE_CXX_SOURCE_FILE_EXTENSIONS c)

CMakeLists.txt

cmake_minimum_required(VERSION 2.8.7 FATAL_ERROR)

set(CMAKE_USER_MAKE_RULES_OVERRIDE "CryptoppMakeRulesOverwrite.cmake")

project(cryptopp CXX)

include(CheckTypeSize)
CHECK_TYPE_SIZE("unsigned short" CMAKE_SIZEOF_UNSIGNED_SHORT)

As @Tsyvarev has commented check_type_size() supports a LANGUAGE parameter, but unfortunately not for CMake version 2.8.7. But this older version does already support CMAKE_USER_MAKE_RULES_OVERRIDE.

So I'm still wondering if not the best solution would be to go to a newer version of CMake (forcing some users of older CMake versions to upgrade). Or writing your own try_compile() snippets.

References

• How to add in a CMake project a global file extension (*.pde) to GCC which is treated like C++ code
• Change default value of CMAKE_CXX_FLAGS_DEBUG and friends in CMake