Faulty detection of C++11 support.

[elfprince13]

if (NOT WIN32)
#http://www.guyrutenberg.com/2014/01/05/enabling-c11-c0x-in-cmake/
include(CheckCXXCompilerFlag)
CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
if(COMPILER_SUPPORTS_CXX11)
	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
    message("-- C++11 Enabled")
elseif(COMPILER_SUPPORTS_CXX0X)
	set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")
    message("-- C++0x Enabled")
else()
        message(STATUS "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
endif()
endif()

This snippet causes configuration to abort on my Linux machine when using clang (clang --version returns the following:

clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

).

However Clang is absolutely a C++11 compliant compiler, and I can manually pass it the -std=c++11 flag without incident.

[pjcozzi]

@elfprince13 thanks for the report, any chance you would be able to contribute a pull request with a fix?

[elfprince13]

I've just commented them out in our fork (https://github.com/Geopipe/COLLADA2GLTF), because it's pretty easy to identify by inspection of error messages when compilation fails due to C++11 not being supported. I suspect you guys will want a more user-friendly fix.

[javagl]

Instead of manually setting the (compiler-specific) flags, it should be possible to just use

set(CMAKE_CXX_STANDARD 11)

(with 98, 11 or 17).

(This might need a CMake version newer than 2.8, though, and .... I cannot test it appropriately right now, so no PR from me here, just as a hint)

[elfprince13]

Yeah, that's I use in other projects, with a for-loop to iterate over both C and CXX (and disable GNU extensions for strict standards compliance). If you think that's a good idea, I'll happily submit the PR here. If it needs a newer CMake version, is there any particular reason not to bump the requirement to something newer?

On Tue, Jun 20, 2017 at 4:40 PM Marco Hutter ***@***.***> wrote: Instead of manually setting the (compiler-specific) flags, it should be possible to just use set(CMAKE_CXX_STANDARD 11) (with 98, 11 or 17). (This might need a CMake version newer than 2.8, though, and .... I cannot test it appropriately right now, so no PR from me here, just as a hint)

-- ~Thomas

[javagl]

Given that the required version (which I think is 3.1) is out for more than a year now (according to https://cmake.org/files/ ), requiring it should be fine, but the decision has to be made by the main maintainers here.

[lasalvavida]

set(CMAKE_CXX_STANDARD 11) is the preferred fix

[elfprince13]

set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_EXTENSIONS OFF)

Is more comprehensive, and standards-enforcing. CMAKE_CXX_STANDARD_REQUIRED is intended to provide the same behavior as the message(STATUS "The compiler ${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.") in the existing code.

[lasalvavida]

This was done in #74.