[SOLVED] Using CMakeLists.txt with multiple targets with different flags

Issue

I'm trying to compile the following file, into two different executables, using CMakeLists.txt.

This file is: main.cpp

#include <iostream>
#include <cassert>

int main(int, char**) {
    std::cout << "Hello, world!\n";
    assert(0);
    return 0;
}

and this is the CMakeLists.txt file

cmake_minimum_required(VERSION 3.0.0)
project(multi_Tar VERSION 0.1.0)


SET(CMAKE_CXX_FLAGS "-O3 -DNDEBUG")
SET(CMAKE_CXX_FLAGS_RELEASE "-O0")
add_executable(multi_Tar main.cpp)

add_executable(tests main.cpp)
set_target_properties(tests PROPERTIES COMPILE_FLAGS "${CMAKE_CXX_FLAGS_RELEASE}")

---

This solution does not work. When I run ./tests I'm not getting an assertion error.

---

The motivation is using the same CMakeLists.txt for testing validity, and to benchmark the same code.

---

Thanks for the help.

Edit after @squareskittles answer:

Thanks for the answer!

(Including the code for the answer:)

cmake_minimum_required(VERSION 3.0.0)
project(multi_Tar VERSION 0.1.0)

add_executable(multi_Tar main.cpp)
# Add the compile options for multi_Tar.
target_compile_definitions(multi_Tar PRIVATE -O3 -DNDEBUG)

add_executable(tests main.cpp)
# Add the compile options for tests.
target_compile_definitions(multi_Tar PRIVATE -O0)

I tried using your solution, but I got the following error:

<command-line>: error: macro names must be identifiers
<command-line>: error: macro names must be identifiers
CMakeFiles/multi_Tar.dir/build.make:62: recipe for target 'CMakeFiles/multi_Tar.dir/main.cpp.o' failed
make[2]: *** [CMakeFiles/multi_Tar.dir/main.cpp.o] Error 1
CMakeFiles/Makefile2:104: recipe for target 'CMakeFiles/multi_Tar.dir/all' failed
make[1]: *** [CMakeFiles/multi_Tar.dir/all] Error 2
Makefile:105: recipe for target 'all' failed
make: *** [all] Error 2

I tried changing the CMakeLists.txt a bit, but did not manage to get it to work.

Also, should the last line in your solution be:

target_compile_definitions(multi_Tar PRIVATE -O0)

or

target_compile_definitions(tests PRIVATE -O0)

Solution

Based on the CMake code, the tests executable should not produce an assertion error. You added the NDEBUG compile definition, which disables the assert macro per the assert documentation.

If you want to apply compile flags to specific CMake targets, you should use the target-specific CMake commands, such as target_compile_options and target_compile_definitions. I'm not sure where you found this CMake code, but manually modifying the CMAKE_CXX_FLAGS* variables is discouraged and typically unnecessary, especially in more recent versions of CMake.

Try something like this instead, to apply the NDEBUG flag only to the multi_Tar target:

cmake_minimum_required(VERSION 3.0.0)
project(multi_Tar VERSION 0.1.0)

add_executable(multi_Tar main.cpp)
# Add the compile options for multi_Tar.
target_compile_options(multi_Tar PRIVATE -O3 -DNDEBUG)

add_executable(tests main.cpp)
# Add the compile options for tests.
target_compile_options(tests PRIVATE -O0)

Answered By - squareskittles