How to enable C++11 in CLion?

Question

I'm trying to run C++11 code in CLion but it doesn't work. It says:

...
    /projects/CLion/untitled/main.cpp:7:1: note: C++11 ‘constexpr’ only available with -std=c++11 or -std=gnu++11
...

I tried to set CMAKE_C_FLAGS to -std=c++11 or -std=gnu++11 but I still have the same problem. Regular C++ code compiles fine.

What flag do I have to set in CLion's CMake window to compile my C++11 code?

Answer 1

I tried to set CMAKE_C_FLAGS

According to the documentation the CMAKE_C_FLAGS set C language flags for all build types. For C++ you need use CMAKE_CXX_FLAGS instead:

set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

Answer 2

For CMake 3.1 or later, you can set the CMAKE_CXX_STANDARD variable to 11:

Default value for CXX_STANDARD property of targets.

This variable is used to initialize the CXX_STANDARD property on all targets.

CXX_STANDARD documentation:

The C++ standard whose features are requested to build this target.

This property specifies the C++ standard whose features are requested to build this target. For some compilers, this results in adding a flag such as -std=gnu++11 to the compile line.

Supported values are 98, 11 and 14.

If the value requested does not result in a compile flag being added for the compiler in use, a previous standard flag will be added instead. This means that using:

set_property(TARGET tgt PROPERTY CXX_STANDARD 11)

with a compiler which does not support -std=gnu++11 or an equivalent flag will not result in an error or warning, but will instead add the -std=gnu++98 flag if supported. This “decay” behavior may be controlled with the CXX_STANDARD_REQUIRED target property.

See the cmake-compile-features(7) manual for information on compile features.

This property is initialized by the value of the CMAKE_CXX_STANDARD variable if it is set when a target is created.