[SOLVED] CMake Add and Remove a Macro definition to compile Shared Library/Executable

Issue

I have a c++ code i need to compile in two ways, a Shared Library and an Executable, In order to do so some of my functions need to be undefined when compiling as a shared library. So i decide to used #ifdef MACRO and define MACRO in my CMakeLists.txt.

Here is my case :

File function.cpp :

#include <iostream>

#ifdef _SHARED_LIBRARY_

void printSharedLibrary(void)
{
    std::cout << "Shared Library" << std::endl;
}

#else

void printExecutable(void)
{
    std::cout << "Executable" << std::endl;
}

#endif

File main.cpp :

#ifdef _SHARED_LIBRARY_
    void printSharedLibrary(void);
#else
    void printExecutable(void);
#endif

int main (void)
{
    #ifdef _SHARED_LIBRARY_
        printSharedLibrary();
    #else
        printExecutable();
    #endif
}

File CMakeLists.txt :

project(ProjectTest)

message("_SHARED_LIBRARY_ ADDED BELOW")
add_definitions(-D_SHARED_LIBRARY_)

add_library(TestLibrary SHARED functions.cpp)
add_executable(DefinedExecutable main.cpp) // Only here to be able to test the library
target_link_libraries(DefinedExecutable TestLibrary)

message("_SHARED_LIBRARY_ REMOVED BELOW")
remove_definitions(-D_SHARED_LIBRARY_)

add_executable(UndefinedExecutable main.cpp functions.cpp)

Output :

$> ./DefinedExecutable
Executable

$> ./UndefinedExecutable
Executable

Expected Output :

$> ./build/DefinedExecutable
Shared Library

$> ./build/UndefinedExecutable
Executable

in order to build it i use : rm -rf build/ ; mkdir build ; cd build ; cmake .. ; make ; cd ..

So my question is Is there a way to define _SHARED_LIBRARY_ for the build of DefinedExecutable and then undefine it for the build of UndefinedExecutable. Thanks for the help

Solution

Use target_compile_definitions to specify compile definitions for the given target:

target_compile_definitions(TestLibrary PUBLIC _SHARED_LIBRARY_)

Then any executable linked against TestLibrary will inherit _SHARED_LIBRARY_ definition.

Answered By - Evg