How do I activate C 11 in CMake

Question

When I try to run a CMake generated makefile to compile my program  I get the error that     range based for loops are not supported in C   98 mode    I tried adding add definitions -std c  0x  to my CMakeLists txt  but it did not help   I tried this too   if CMAKE COMPILER IS GNUCXX      add definitions -std gnu  0x  endif     When I do g   --version  I get      g    Ubuntu Linaro 4 6 1-9ubuntu3  4 6 1   I have also tried SET CMAKE CXX FLAGS  -std c  0x    which also does not work   I do not understand how I can activate C   11 features using CMake

User · Answer

The CMake command target compile features   is used to specify the required C   feature cxx range for  CMake will then induce the C   standard to be used   cmake minimum required VERSION 3 1 0 FATAL ERROR  project foobar CXX  add executable foobar main cc  target compile features foobar PRIVATE cxx range for    There is no need to use add definitions -std c  11  or to modify the CMake variable CMAKE CXX FLAGS  because CMake will make sure the C   compiler is invoked with the appropriate command line flags   Maybe your C   program uses other C   features than cxx range for  The CMake global property CMAKE CXX KNOWN FEATURES lists the C   features you can choose from   Instead of using target compile features   you can also specify the C   standard explicitly by setting the CMake properties  CXX STANDARD  and  CXX STANDARD REQUIRED for your CMake target   See also my more detailed answer

User · Answer

I am using  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   elseif COMPILER SUPPORTS CXX0X      set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -std c  0x   else           message STATUS  The compiler   CMAKE CXX COMPILER  has no C  11 support  Please use a different C   compiler    endif     But if you want to play with C  11  g   4 6 1 is pretty old  Try to get a newer g   version

User · Answer

This is another way of enabling C  11 support   ADD DEFINITIONS      -std c  11   Or -std c  0x       Other flags     I have encountered instances where only this method works and other methods fail  Maybe it has something to do with the latest version of CMake

User · Answer

In case you want to always activate the latest C   standard  here s my extension of David Grayson s answer  in light of the recent  CMake 3 8 and CMake 3 11  additions of values of 17 and 20 for CMAKE CXX STANDARD    IF  CMAKE VERSION VERSION LESS  3 8       SET CMAKE CXX STANDARD 14  ELSEIF  CMAKE VERSION VERSION LESS  3 11       SET CMAKE CXX STANDARD 17  ELSE       SET CMAKE CXX STANDARD 20  ENDIF      Typically  you ll also want to turn off compiler-specific extensions  SET CMAKE CXX EXTENSIONS OFF     Use that code in the place of set  CMAKE CXX STANDARD 11  in the linked answer

User · Answer

I think just these two lines are enough   set CMAKE CXX STANDARD 11   set CMAKE CXX FLAGS    CMAKE CXX FLAGS  -std c  11

User · Answer

CMake 3 1 introduced the CMAKE CXX STANDARD variable that you can use   If you know that you will always have CMake 3 1 or later available  you can just write this in your top-level CMakeLists txt file  or put it right before any new target is defined  set  CMAKE CXX STANDARD 11   If you need to support older versions of CMake  here is a macro I came up with that you can use  macro use cxx11    if  CMAKE VERSION VERSION LESS  quot 3 1 quot       if  CMAKE CXX COMPILER ID STREQUAL  quot GNU quot         set  CMAKE CXX FLAGS  quot   CMAKE CXX FLAGS  -std gnu  11 quot       endif      else        set  CMAKE CXX STANDARD 11    endif    endmacro use cxx11   The macro only supports GCC right now  but it should be straight-forward to expand it to other compilers  Then you could write use cxx11   at the top of any CMakeLists txt file that defines a target that uses C  11  CMake issue  15943 for clang users targeting macOS If you are using CMake and clang to target macOS there is a bug that can cause the CMAKE CXX STANDARD feature to simply not work  not add any compiler flags    Make sure that you do one of the following things   Use cmake minimum required to require CMake 3 0 or later  or  Set policy CMP0025 to NEW with the following code at the top of your CMakeLists txt file before the project command      Fix behavior of CMAKE CXX STANDARD when targeting macOS    if  POLICY CMP0025      cmake policy SET CMP0025 NEW    endif

User · Answer

OS X and Homebrew LLVM related   Don t forget to call cmake minimum required VERSION 3 3  and project   after it   Or CMake will insert project   implicitly before line 1  causing trouble with Clang version detection and possibly other sorts of troubles  Here is a related issue

User · Answer

On modern CMake     3 1  the best way to set global requirements is   set CMAKE CXX STANDARD 11  set CMAKE CXX STANDARD REQUIRED ON  set CMAKE CXX EXTENSIONS OFF    It translates to  I want C  11 for all targets  it s not optional  I don   t want to use any GNU or Microsoft  extensions   As of C  17  this still is IMHO the best way   Source  Enabling C  11 And Later In CMake

User · Answer

The easiest way   add compile options -std c  11

User · Answer

The easiest way to set the Cxx standard is    set property TARGET tgt PROPERTY CXX STANDARD 11    See the CMake documentation for more details

User · Answer

As it turns out  SET CMAKE CXX FLAGS  -std c  0x   does activate many C  11 features  The reason it did not work was that the statement looked like this   set CMAKE CXX FLAGS  -std c  0x   CMAKE CXX FLAGS  -g -ftest-coverage -fprofile-arcs     Following this approach  somehow the -std c  0x flag was overwritten and it did not work  Setting the flags one by one or using a list method is working   list  APPEND CMAKE CXX FLAGS  -std c  0x   CMAKE CXX FLAGS  -g -ftest-coverage -fprofile-arcs

User · Answer

Modern cmake offers simpler ways to configure compilers to use a specific version of C    The only thing anyone needs to do is set the relevant target properties  Among the properties supported by cmake  the ones that are used to determine how to configure compilers to support a specific version of C   are the following    CXX STANDARD sets the C   standard whose features are requested to build the target  Set this as 11 to target C  11  CXX EXTENSIONS  a boolean specifying whether compiler specific extensions are requested   Setting this as Off disables support for any compiler-specific extension    To demonstrate  here is a minimal working example of a CMakeLists txt   cmake minimum required VERSION 3 1   project testproject LANGUAGES CXX    set testproject SOURCES     main c          add executable testproject   testproject SOURCES    set target properties testproject     PROPERTIES     CXX STANDARD 11     CXX EXTENSIONS off

User · Answer

For CMake 3 8 and newer you can use  target compile features target PUBLIC cxx std 11

User · Answer

What works for me is to set the following line in your CMakeLists txt   set  CMAKE CXX FLAGS    CMAKE CXX FLAGS  -std c  11     Setting this command activates the C  11 features for the compiler and after executing the cmake    command  you should be able to use range based for loops in your code and compile it without any errors

[c++11] How do I activate C++ 11 in CMake?

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