Set CFLAGS and CXXFLAGS options using CMake

cmake cflags
majie picture majie · Apr 10, 2012 · Viewed 178.5k times · Source

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

Fraser picture Fraser · Apr 10, 2012

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")

Related questions

How do I add a linker or compile flag in a CMake file?

I am using the arm-linux-androideabi-g++ compiler. When I try to compile a simple "Hello, World!" program it compiles fine. When I test it by adding a simple exception handling in that code it works too (after adding -fexceptions .. I guess …

Read More
Debug vs Release in CMake

In a GCC compiled project, How do I run CMake for each target type (debug/release)? How do I specify debug and release C/C++ flags using CMake? How do I express that the main executable will be compiled with …

Read More
How to properly add include directories with CMake

About a year ago I asked about header dependencies in CMake. I realized recently that the issue seemed to be that CMake considered those header files to be external to the project. At least, when generating a Code::Blocks project …

Read More