Conflicting C++11 flags when compiling with GCC

[Smjert]

medusa cmake file adds -std=c++11 flag for gcc but ogdf submodule uses -std=gnu++0x so the OpenMP flag test can't compile (and i suppose the same would happen with the project later).

[wisk]

I'm not sure to understand this problem, so don't hesitate to bring more information if I'm wrong. IIRC CMake doesn't provide a generic way to enable C++11 feature and I have no idea how to implement it properly. Do you think this test could fix this issue?

[Smjert]

The problem is that the medusa root CmakeLists.txt adds -std=c++11 flag if you use GCC (line 72 and 73) but ogdf projects adds -std=gnu++0x if you use GCC (line 33-34). Those are two conflicting flags that prevents cmake (and the project) to compile. It should be set only once in the medusa root project, and it should be set to c++11. I understand that the other project checks and adds the flag because you can compile it "alone", though there should be a way to check if the flag is already set, so if medusa set it, ogdf wont.

What you're saying is another issue: testing if a compiler support c++11 or not. But i don't think is necessary here because you are using c++11 code, so the flag should be enforced.

[saeschdivara]

I had the problem that for clang a false flag was added, so I am using some code from a dependency of your project which looks like this:

# Enable C++11
if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" OR EMSCRIPTEN)
        list(APPEND CMAKE_CXX_FLAGS "-std=c++11 -stdlib=libc++")
elseif("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
        list(APPEND CMAKE_CXX_FLAGS "-std=gnu++0x -fno-operator-names")
endif()

[wisk]

Hi,

It should be fixed with set(CMAKE_CXX_STANDARD 11), feel free to re-open this issue if it doesn't work.

Thanks