Set CFLAGS and CXXFLAGS options using CMake

Question

I just want to debug some code running on Linux and I need a debug build (-O0 -ggdb). So I added these things to my CMakeLists.txt:

set(CMAKE_BUILD_TYPE DEBUG) set(CMAKE_C_FLAGS "-O0 -ggdb") set(CMAKE_C_FLAGS_DEBUG "-O0 -ggdb") set(CMAKE_C_FLAGS_RELEASE "-O0 -ggdb") set(CMAKE_CXX_FLAGS "-O0 -ggdb") set(CMAKE_CXX_FLAGS_DEBUG "-O0 -ggdb") set(CMAKE_CXX_FLAGS_RELEASE "-O0 -ggdb") 

When I tried to compile I turned verbose on using make VERBOSE=1 And I observed the output, like this

... /usr/bin/c++ -D_BSD_SOURCE **-O0 -ggdb** -Wnon-virtual-dtor  -Wno-long-long -ansi -Wundef -Wcast-align -Wchar-subscripts -Wall -W  -Wpointer-arith -Wformat-security -fno-exceptions -DQT_NO_EXCEPTIONS  -fno-check-new -fno-common -Woverloaded-virtual -fno-threadsafe-statics  -fvisibility=hidden -fvisibility-inlines-hidden **-g -O2**  -fno-reorder-blocks -fno-schedule-insns -fno-inline ... 

Apparently the code is compiled with "-g -O2" and this is not what I want. How can I force it to use "-O0 -ggdb" only?

Answer 1

You need to set the flags after the project command in your CMakeLists.txt.

Also, if you're calling include(${QT_USE_FILE}) or add_definitions(${QT_DEFINITIONS}), you should include these set commands after the Qt ones since these would append further flags. If that is the case, you maybe just want to append your flags to the Qt ones, so change to e.g.

set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O0 -ggdb") 

Answer 2

The easiest solution working fine for me is this:

export CFLAGS=-ggdb export CXXFLAGS=-ggdb 

CMake will append them to all configurations' flags. Just make sure to clear CMake cache.