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IDProjectCategoryView StatusDate SubmittedLast Update
0015316CMakeCMakepublic2014-12-18 08:462016-06-10 14:31
Reporterlucaghera 
Assigned ToKitware Robot 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionmoved 
PlatformApple MacOSOS XOS Version10.4.10
Product VersionCMake 3.0.2 
Target VersionFixed in Version 
Summary0015316: Generation of Eclipse project does not provide support for c++ 11
DescriptionI’m writing a CMake file for a project that should be compiled both in Ubuntu and OS X.
I want to use eclipse as IDE, gcc and C++ 11.

I read different threads that suggest how to enable C++ 11 in eclipse.
According to them I included these lines in my CMake:

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

if (${CMAKE_EXTRA_GENERATOR} MATCHES "Eclipse CDT4")
    set(CMAKE_CXX_COMPILER_ARG1 "-std=c++11" CACHE STRING "C++ version for eclipse" FORCE)
    set(CMAKE_ECLIPSE_VERSION "4.3" CACHE STRING "Eclipse version" FORCE)
endif (${CMAKE_EXTRA_GENERATOR} MATCHES "Eclipse CDT4”)

However, eclipse still set a wrong value for the symbol __cplusplus (199711L instead of 201103L I guess). In the generated file .cproject this should be the line <pathentry kind="mac" name="__cplusplus" path="" value="199711L"/> (in my case 265)
For this reason eclipse is not able to index C++ 11 features such as shared pointer.
Therefore I get a syntax error also if the code compiles.
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  Notes
(0037479)
Brad King (manager)
2014-12-18 09:04

 I think this was fixed in 'master' recently by these commits:

 Code Blocks/Eclipse: Use non-default stdlib includes when specified.
 http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=45a25d63 [^]

 Code Blocks/Eclipse: Add -std= flag matching.
 http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=eaf6f67f [^]

Please build from source or try a nightly binary: http://www.cmake.org/files/dev/?C=M;O=D [^]
(0037480)
lucaghera (reporter)
2014-12-18 09:17

 I just tried to download the version cmake-3.1.20141217-g9a64b on both Mac and Ubuntu.

The generated .cproject is still incorrect.
The variable __cplusplus is still set to 199711L
<pathentry kind="mac" name="__cplusplus" path="" value="199711L"/>
(0037481)
Brad King (manager)
2014-12-18 09:27

 Try hacking on Modules/CMakeExtraGeneratorDetermineCompilerMacrosAndIncludeDirs.cmake get it to extract the __cplusplus builtin definition from its trial run of the compiler.
(0037493)
lucaghera (reporter)
2014-12-19 04:36

 Here are some preliminary results.
I did it on MAC.

a) It seems that the variable in which all the defines are stored is the variable ${_gccStdout}
b) For some reason that is not yet clear to me, when CMake run the command to infer the #defines this variable is empty and the variable ${_gccOutput} contains "g++-4.9: error: -std=c++11: No such file or directory".

This error does not happen if I don't set the language (i.e. project(NAME CXX)).
However in that case the default language seems to be C and the code doesn't use the CXX_ARG_1 containing std=c++11.
(0037497)
Brad King (manager)
2014-12-19 08:34

 Re 0015316:0037493: Thanks for looking into it. To debug the call to g++, just before the execute_process line add:

message("'${_compilerExecutable}' '${_arg1}' '${_stdver}' '${_stdlib}' '-v' '-E' '-x' '${_lang}' '-dD' 'dummy'")

This should show exactly what command is being executed.
(0037944)
Andrea Salvi (reporter)
2015-02-07 08:09

 I can confirm this happening also in cmake 3.1.2.
I'm using Xubuntu 14.04 LTS 64bit.

Here is my CMakeList.txt snippet with which I enable C++11:

include(CheckCXXCompilerFlag)
CHECK_CXX_COMPILER_FLAG("-std=c++11" COMPILER_SUPPORTS_CXX11)
if(COMPILER_SUPPORTS_CXX11)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
else()
    message(FATAL_ERROR "${CMAKE_CXX_COMPILER} has no C++11 support. Please use a different C++ compiler.")
endif()

if(${CMAKE_EXTRA_GENERATOR} MATCHES "Eclipse CDT4")
    set(CMAKE_CXX_COMPILER_ARG1 "-std=c++11" CACHE STRING "C++ version for eclipse" FORCE)
    set(CMAKE_ECLIPSE_VERSION "4.4" CACHE STRING "Eclipse version" FORCE)
endif()

I have checked how g++ is being called while building my project and the -std=c++11 argument is present.
(0037987)
Andrea Salvi (reporter)
2015-02-17 06:01

 Ok, I think I managed to understand why this behavior happened.

Initially, this is the g++ call that was used to fetch all of the compiler's properties and flags:

/usr/bin/c++ -v -E -x c++ -dD dummy

This way the compiler uses the C++98 standard, which is apparently the default for GCC 4.8, shipped with Ubuntu 14.04 and its derivatives.

To force the compiler to use the C++11 standard, I had to prepend

if(${CMAKE_EXTRA_GENERATOR} MATCHES "Eclipse CDT4")
    set(CMAKE_CXX_COMPILER_ARG1 "-std=c++11" CACHE STRING "C++ version for eclipse" FORCE)
    set(CMAKE_ECLIPSE_VERSION "4.4" CACHE STRING "Eclipse version" FORCE)
endif()

before the project() declaration. This way, the call to g++ became

/usr/bin/c++ -std=c++11 -v -E -x c++ -dD dummy

and the Eclipse project file was set with the correct properties.
(0040514)
Gregory Kramida (reporter)
2016-02-19 10:29
edited on: 2016-02-19 10:31

 Hi all, thank you all for looking into this issue to date. Apparently, this issue is still around and is possibly causing indexer errors in Eclipse CDT (on any OS), even with the -std=c++11 manually included in the parser options. Value of __cplusplus, using the lastest CMake build, is still incorrect without using the workaround graciously provided by @Andrea Salvi.

Is it possible to fix this so that the generator takes the C++ standard flags into account when querying gcc to make the CDT project file?

-Thanks
(0042692)
Kitware Robot (administrator)
2016-06-10 14:29

 Resolving issue as `moved`.

This issue tracker is no longer used. Further discussion of this issue may take place in the current CMake Issues page linked in the banner at the top of this page.

 Issue History
Date Modified Username Field Change
2014-12-18 08:46 lucaghera New Issue
2014-12-18 09:04 Brad King Note Added: 0037479
2014-12-18 09:17 lucaghera Note Added: 0037480
2014-12-18 09:27 Brad King Note Added: 0037481
2014-12-19 04:36 lucaghera Note Added: 0037493
2014-12-19 08:34 Brad King Note Added: 0037497
2015-02-07 08:09 Andrea Salvi Note Added: 0037944
2015-02-17 06:01 Andrea Salvi Note Added: 0037987
2016-02-19 10:29 Gregory Kramida Note Added: 0040514
2016-02-19 10:31 Gregory Kramida Note Edited: 0040514
2016-06-10 14:29 Kitware Robot Note Added: 0042692
2016-06-10 14:29 Kitware Robot Status new => resolved
2016-06-10 14:29 Kitware Robot Resolution open => moved
2016-06-10 14:29 Kitware Robot Assigned To => Kitware Robot
2016-06-10 14:31 Kitware Robot Status resolved => closed

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