Override compilation flags for individual files

Question

I would like to use a global set of flags to compile the project, which means that in my top-level CMakeLists.txt file, I specified:

ADD_DEFINITIONS ( -Wall -Weffc++ -pedantic -std=c++0x ) 

However, for a specific file (say, "foo.cpp") in a subdirectory, I want to switch compile flags so that I don't use -WeffC ++ (including a commercial library that I cannot change). To simplify things, to use only -Wall, I tried:

  SET_SOURCE_FILES_PROPERTIES( foo.cpp PROPERTIES COMPILE_FLAGS -Wall ) ADD_EXECUTABLE( foo foo.cpp ) 

which did not work. I also tried

 SET_PROPERTY( SOURCE foo.cpp PROPERTY COMPILE_FLAGS -Wall ) ADD_EXECUTABLE( foo foo.cpp ) 

and

 ADD_EXECUTABLE( foo foo.cpp ) SET_TARGET_PROPERTIES( foo PROPERTIES COMPILE_FLAGS -Wall ) 

which did not work.

Finally, I tried to remove this error:

 REMOVE_DEFINITIONS( -Weffc++ ) ADD_EXECUTABLE( foo foo.cpp ) ADD_DEFINITIONS( -Weffc++ ) 

which also didn’t work (that is, I get a lot of style warnings in the commercial library). (** Note: ARE warnings are suppressed if I DO NOT re-enable the -WeffC ++ directive after creating the executable.)

I also tried temporarily removing the compilation flags: http://www.cmake.org/pipermail/cmake/2007-June/014614.html , but that didn't help.

Is there an elegant solution for this?

Answer 1

Your attempts above add extra flags to your file / target, rather than overwriting what you seem to expect. For example, from the documentation for set_source_files_properties(foo.cpp PROPERTIES COMPILE_FLAGS -Wno-effc++)

This should add -Wno-effc++ after -Weffc++ to the compiler command, and the last setting will be defeated. To see the full command and verify that this is true, you can do

 make VERBOSE=1 

As one of the proponents of the GNU standard library, C ++ presents a rather negative opinion about -Weffc++ 's.

Another point is that you are misusing what you are using for compiler flags, and not for alleged preprocessor definitions.

It would be preferable to use

 add_compile_options(-Wall -Weffc++ -pedantic -std=c++0x) 

or for versions of CMake <3.0 to do something more:

 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Weffc++ -pedantic -std=c++0x") 

In response to further questions in the comments below, I find it impossible to reliably remove the flag in a single file. The reason is that for any given source file it has ^{1 of} its target, but they are not displayed in any of the properties of this source file.

You can see how to remove the problem flag from the target COMPILE_OPTIONS , and then apply it to each of the target sources separately, dropping it from a specific source file as necessary.

However, while this may work in many scenarios, it has several problems.

First do not include COMPILE_OPTIONS , only COMPILE_FLAGS . This is a problem because COMPILE_OPTIONS targets may include, but COMPILE_FLAGS does not support them. Thus, you will have to adapt the generator expressions while searching for your flag, and even you may even have to “parse” the generator expressions if your flag was contained in one or more to see if it should be reapplied to the remaining source files.

The second - with CMake v3.0, targets can indicate. This means that your target’s dependency can add or override the target COMPILE_OPTIONS through its INTERFACE_COMPILE_OPTIONS . Thus, you will also have to recursively iterate over all your target dependencies (not a very simple task, since the list for the target may also contain generator expressions) to find any that apply the problem flag and try to remove ' INTERFACE_COMPILE_OPTIONS from these goals as well.

At this point in complexity, I would like to introduce a patch for CMake to provide functionality to remove a specific flag unconditionally from the source file.

1: Note that unlike the COMPILE_FLAGS property in the source files, the COMPILE_FLAGS property is COMPILE_FLAGS for purposes.

Answer 2

Just adding the correct @Fraser answer.

If you want to add a special flag to specific folders, you can do:

 file(GLOB SPECIAL_SRC_FILES "path/one/src/*.cpp" "path/two/src/*.cpp") set_property(SOURCE ${SPECIAL_SRC_FILES} PROPERTY COMPILE_FLAGS -Wno-effc++) 

or

 file(GLOB SPECIAL_SRC_FILES "path/one/src/*.cpp" "path/two/src/*.cpp") set_source_files_properties(${SPECIAL_SRC_FILES} PROPERTIES COMPILE_FLAGS -Wno-effc++) 

Please note that GLOB is not recommended, as discussed here.