Debug vs Release in CMake

With CMake, it's generally recommended to do an "out of source" build. Create your CMakeLists.txt in the root of your project. Then from the root of your project:

mkdir Releasecd Releasecmake -DCMAKE_BUILD_TYPE=Release ..make

And for Debug (again from the root of your project):

mkdir Debugcd Debugcmake -DCMAKE_BUILD_TYPE=Debug ..make

Release / Debug will add the appropriate flags for your compiler. There are also RelWithDebInfo and MinSizeRel build configurations.

You can modify/add to the flags by specifying a toolchain file in which you can add CMAKE_<LANG>_FLAGS_<CONFIG>_INIT variables, e.g.:

set(CMAKE_CXX_FLAGS_DEBUG_INIT "-Wall")set(CMAKE_CXX_FLAGS_RELEASE_INIT "-Wall")

See CMAKE_BUILD_TYPE for more details.

As for your third question, I'm not sure what you are asking exactly. CMake should automatically detect and use the compiler appropriate for your different source files.

For debug/release flags, see the CMAKE_BUILD_TYPE variable (you pass it as cmake -DCMAKE_BUILD_TYPE=value). It takes values like Release, Debug, etc.

https://gitlab.kitware.com/cmake/community/wikis/doc/cmake/Useful-Variables#compilers-and-tools

cmake uses the extension to choose the compiler, so just name your files .c.

You can override this with various settings:

For example:

set_source_files_properties(yourfile.c LANGUAGE CXX) 

Would compile .c files with g++. The link above also shows how to select a specific compiler for C/C++.

Instead of manipulating the CMAKE_CXX_FLAGS strings directly (which could be done more nicely using string(APPEND CMAKE_CXX_FLAGS_DEBUG " -g3") btw), you can use add_compile_options:

add_compile_options(  "-Wall" "-Wpedantic" "-Wextra" "-fexceptions"  "$<$<CONFIG:DEBUG>:-O0;-g3;-ggdb>")

This would add the specified warnings to all build types, but only the given debugging flags to the DEBUG build. Note that compile options are stored as a CMake list, which is just a string separating its elements by semicolons ;.