The issue is that GCC 4.8 c++1y does offer support for some c++14
features ( https://gcc.gnu.org/projects/cxx-status.html#cxx14 ) and
therefore that is why you getting a compile time failure. You could
try using target_compile_features instead but it only verifies
language level features and is not aware of standard library features
such as std::string_literals.
On Tue, Mar 7, 2017 at 9:32 AM, Winfried <winfried_...@xmsnet.nl> wrote:
> I am trying to let cmake exit with an error when the c++ compiler doesn't
> support at least the C++14 standard.
> According to the cmake documentation this should be possible with variables
> CMAKE_CXX_STANDARD and CMAKE_CXX_STANDARD_REQUIRED.
>
> However when I compile the simple helloworld example below with g++ 4.8
> (which has no C++14 support), cmake supplies the option -std=c++1y to g++
> and compilation fails.
> I expected CMake to stop during configure with an error.
>
> Can anybody see what I am doing wrong ?
>
> Thanks in advance,
> Winfried
>
>
> file main.cpp :
>
> #include <string>
> #include <iostream>
>
> using namespace std::string_literals;
>
> int main(int, char **)
> {
> std::cout << "Hello "s + "world!" << std::endl;
> return 0;
> }
>
>
>
> file CMakeLists.txt :
>
> project(reqstd_test)
> cmake_minimum_required(VERSION 3.7)
>
> set(CMAKE_CXX_STANDARD 14)
> set(CMAKE_CXX_STANDARD_REQUIRED ON)
> set(CMAKE_CXX_EXTENSIONS OFF)
>
> add_executable(hello main.cpp)
>
>
> cmake output:
> wdobbe@linux-wdobbe:/data/generated/cmake_std_req/build> cmake ..
> -- The C compiler identification is GNU 4.8.5
> -- The CXX compiler identification is GNU 4.8.5
> -- Check for working C compiler: /usr/bin/cc
> -- Check for working C compiler: /usr/bin/cc -- works
> -- Detecting C compiler ABI info
> -- Detecting C compiler ABI info - done
> -- Detecting C compile features
> -- Detecting C compile features - done
> -- Check for working CXX compiler: /usr/bin/c++
> -- Check for working CXX compiler: /usr/bin/c++ -- works
> -- Detecting CXX compiler ABI info
> -- Detecting CXX compiler ABI info - done
> -- Detecting CXX compile features
> -- Detecting CXX compile features - done
> -- Configuring done
> -- Generating done
> -- Build files have been written to: /data/generated/cmake_std_req/build
> wdobbe@linux-wdobbe:/data/generated/cmake_std_req/build>
>
>
> make output:
> wdobbe@linux-wdobbe:/data/generated/cmake_std_req/build> make VERBOSE=Y
> /home/wdobbe/install/cmake-3.8.0-rc2-Linux-x86_64/bin/cmake
> -H/data/generated/cmake_std_req -B/data/generated/cmake_std_req/build
> --check-build-system CMakeFiles/Makefile.cmake 0
> <cut>
> [ 50%] Building CXX object CMakeFiles/hello.dir/main.cpp.o
> /usr/bin/c++ -std=c++1y -o CMakeFiles/hello.dir/main.cpp.o -c
> /data/generated/cmake_std_req/main.cpp
> /data/generated/cmake_std_req/main.cpp:4:22: error: ‘string_literals’ is not
> a namespace-name
> using namespace std::string_literals;
> ^
> /data/generated/cmake_std_req/main.cpp:4:37: error: expected namespace-name
> before ‘;’ token
> using namespace std::string_literals;
> ^
> /data/generated/cmake_std_req/main.cpp: In function ‘int main(int, char**)’:
> /data/generated/cmake_std_req/main.cpp:8:18: error: unable to find string
> literal operator ‘operator"" s’
> std::cout << "Hello "s + "world!" << std::endl;
> ^
> CMakeFiles/hello.dir/build.make:62: recipe for target
> 'CMakeFiles/hello.dir/main.cpp.o' failed
> make[2]: *** [CMakeFiles/hello.dir/main.cpp.o] Error 1
> make[2]: Leaving directory '/data/generated/cmake_std_req/build'
> CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/hello.dir/all' failed
> make[1]: *** [CMakeFiles/hello.dir/all] Error 2
> make[1]: Leaving directory '/data/generated/cmake_std_req/build'
> Makefile:83: recipe for target 'all' failed
> make: *** [all] Error 2
>
> --
>
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