Preventing CMake-generated makefile for optional-header-only library from compiling source files in header-only mode

Question

I have a library that can both be used as an header-only library and as a traditional library. To enable this optional-header-only functionality, the library includes

.cpp

source files if compiled in header-only mode. Example:

// Vector.hpp 

// (Module file), intended to be included manually by the user

#ifndef LIBRARY_MODULE_VECTOR

#define LIBRARY_MODULE_VECTOR



#include "Library/Vector/Inc/Vector2.hpp"

#include "Library/Vector/Inc/Vector3.hpp"

#include "Library/Vector/Inc/VectorUtils.hpp"



#if defined(LIBRARY_HEADERONLY)

    #include "Library/Vector/Src/Vector2.cpp"

    #include "Library/Vector/Src/Vector3.cpp"

    #include "Library/Vector/Src/VectorUtils.cpp"

#endif



#endif

When the user includes

Vector.hpp

in one of his projects, if

LIBRARY_HEADERONLY

is defined, the implementation source files will be included right after the header files. Careful usage of the

inline

keyword is applied to avoid multiple definitions.

If

LIBRARY_HEADERONLY

is undefined, the

.cpp

files will be compiled and the library will have to be linked.

My build system of choice is CMake.

Using a CMake flag, the user can define or undefine

LIBRARY_HEADERONLY

.

The

CMakeLists.txt

file is similar to this:

# (not shown) set flag and cache variables...



# Include library directory

include_directories("./${INCLUDE_DIRECTORY}")



# Glob all library header/source files

file(GLOB_RECURSE SRC_LIST "${INC_DIR}/*" "${SRC_DIR}/*")



# (not shown) check if header-only mode is enabled

# (from now on we assume header-only mode is enabled and that

# LIBRARY_HEADERONLY is defined)



# Use all source/header files as a library target

add_library(HEADER_ONLY_TARGET STATIC ${SRC_LIST})

set_target_properties(HEADER_ONLY_TARGET PROPERTIES LINKER_LANGUAGE CXX)

install(DIRECTORY ${INC_DIR} DESTINATION .)

Unfortunately, the CMake-generated makefile always compiles the

.cpp

files, even when header-only mode is enabled and the target is

HEADER_ONLY_TARGET

.

How can I prevent the CMake-generated makefile from compiling the source files in header-only mode?

Note that IDEs reliant on CMake-generated output, such as QTCreator, should display both the header and source files as part of the project.

If I don't glob any source file, but only the

.hpp

header files, CMake will complain that no source files were selected for a library target, and IDEs that rely on CMake files will not display any item.

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Answer 1

Try setting the source files' HEADER_FILE_ONLY property to prevent them from building, e.g.:

if (LIBRARY_HEADERONLY)
    set_source_files_properties(${SRC_LIST} PROPERTIES HEADER_FILE_ONLY 1)
    ...
endif()

Also see the documentation.

Preventing CMake-generated makefile for optional-header-only library from compiling source files in header-only mode

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