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

User · Answer

On Unix systems  for several projects  I added these lines into the CMakeLists txt and it was compiling successfully because base   usr include  and local includes   usr local include  go into separated directories   set CMAKE C FLAGS    CMAKE C FLAGS  -I usr local include -L usr local lib   set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -I usr local include   set CMAKE EXE LINKER FLAGS    CMAKE EXE LINKER FLAGS  -L usr local lib     It appends the correct directory  including paths for the C and C   compiler flags and the correct directory path for the linker flags   Note  C   compiler  c    doesn t support -L  so we have to use CMAKE EXE LINKER FLAGS

User · Answer

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

User · Answer

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

User · Answer

You must change the cmake C CXX default FLAGS    According to CMAKE BUILD TYPE  DEBUG MINSIZEREL RELWITHDEBINFO RELEASE  put in the main CMakeLists txt one of    For C  set CMAKE C FLAGS DEBUG  put your flags   set CMAKE C FLAGS MINSIZEREL  put your flags   set CMAKE C FLAGS RELWITHDEBINFO  put your flags   set CMAKE C FLAGS RELEASE  put your flags     For C    set CMAKE CXX FLAGS DEBUG  put your flags   set CMAKE CXX FLAGS MINSIZEREL  put your flags   set CMAKE CXX FLAGS RELWITHDEBINFO  put your flags   set CMAKE CXX FLAGS RELEASE  put your flags     This will override the values defined in CMakeCache txt

[cmake] Set CFLAGS and CXXFLAGS options using CMake

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