MantisBT - CMake
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IDProjectCategoryView StatusDate SubmittedLast Update
0015361CMakeCMakepublic2015-01-19 18:282016-06-10 14:31
ReporterLaurent Demailly 
Assigned ToKitware Robot 
PrioritynormalSeveritymajorReproducibilityalways
StatusclosedResolutionmoved 
PlatformLinuxOSUbuntuOS Version14.04.1
Product VersionCMake 3.1 
Target VersionFixed in Version 
Summary0015361: CHECK_CXX_SOURCE_COMPILES doesn't use c++11 flags specified
DescriptionI have

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED on)

in my cmake file - yet later when I try:

check_cxx_source_compiles(
"extern \"C\" void cmkcheckweak() __attribute__((weak));
int main(int argc, char** argv) {
  return cmkcheckweak == nullptr; // works with (void*)0;
}" HAVE_WEAK_SYMBOLS)

it fails incorrectly because it invokes the compiler without the -std=gnu++11 it adds for regular files

(the goal/point of CMAKE_CXX_STANDARD_REQUIRED is to use that compiler for everything and not me having to write code to guess the way to request c++11 compiler)

this is related to http://public.kitware.com/Bug/view.php?id=15359 [^]
but while here there is an easy work around (not use nullptr and use 0 instead) that won't work for other tests I'm trying to do with CHECK_CXX_SOURCE_COMPILES

suggestions/workarounds on how to make CHECK_CXX_SOURCE_COMPILES use the same compiler invocation as my other targets would be most welcome in the meantime
Steps To Reproducesee above and below
Additional InformationPerforming C++ SOURCE FILE Test HAVE_WEAK_SYMBOLS failed with the following output:
Change Dir: /home/ldemailly/mac/wdt_ubuntu_build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTryCompileExec1489303762/fast"
/usr/bin/make -f CMakeFiles/cmTryCompileExec1489303762.dir/build.make CMakeFiles/cmTryCompileExec1489303762.dir/build
make[1]: Entering directory `/mnt/hgfs/ldemailly/wdt_ubuntu_build/CMakeFiles/CMakeTmp'
/usr/local/bin/cmake -E cmake_progress_report /home/ldemailly/mac/wdt_ubuntu_build/CMakeFiles/CMakeTmp/CMakeFiles 1
Building CXX object CMakeFiles/cmTryCompileExec1489303762.dir/src.cxx.o
/usr/bin/c++ -DHAVE_WEAK_SYMBOLS -o CMakeFiles/cmTryCompileExec1489303762.dir/src.cxx.o -c /home/ldemailly/mac/wdt_ubuntu_build/CMakeFiles/CMakeTmp/src.cxx
/home/ldemailly/mac/wdt_ubuntu_build/CMakeFiles/CMakeTmp/src.cxx: In function ‘int main(int, char**)’:
/home/ldemailly/mac/wdt_ubuntu_build/CMakeFiles/CMakeTmp/src.cxx:3:26: error: ‘nullptr’ was not declared in this scope
   return cmkcheckweak == nullptr; // (void*)0; works
                          ^
make[1]: Leaving directory `/mnt/hgfs/ldemailly/wdt_ubuntu_build/CMakeFiles/CMakeTmp'
make[1]: *** [CMakeFiles/cmTryCompileExec1489303762.dir/src.cxx.o] Error 1
make: *** [cmTryCompileExec1489303762/fast] Error 2

Source file was:
extern "C" void cmkcheckweak() __attribute__((weak));
int main(int argc, char** argv) {
  return cmkcheckweak == nullptr; // (void*)0; works
}
TagsNo tags attached.
Relationships
has duplicate 0015550closed  check_cxx_source_compiles() does not honor CMAKE_CXX_STANDARD 
related to 0015359closed Kitware Robot __attribute__((weak)) support/detection (weak symbols) 
Attached Files
Issue History
Date ModifiedUsernameFieldChange
2015-01-19 18:28Laurent DemaillyNew Issue
2015-01-19 20:05Laurent DemaillyNote Added: 0037755
2015-01-20 08:31Brad KingRelationship addedrelated to 0015359
2015-01-20 14:05Laurent DemaillyNote Added: 0037757
2015-01-21 08:29Brad KingNote Added: 0037760
2015-05-01 13:29Brad KingRelationship addedhas duplicate 0015550
2015-07-10 01:12Roman80Note Added: 0039119
2015-08-17 20:02Laurent DemaillyNote Added: 0039292
2015-08-17 20:24Laurent DemaillyNote Added: 0039293
2016-06-10 14:29Kitware RobotNote Added: 0042701
2016-06-10 14:29Kitware RobotStatusnew => resolved
2016-06-10 14:29Kitware RobotResolutionopen => moved
2016-06-10 14:29Kitware RobotAssigned To => Kitware Robot
2016-06-10 14:31Kitware RobotStatusresolved => closed

Notes
(0037755)
Laurent Demailly   
2015-01-19 20:05   
found a temporary workaround:

set(CMAKE_REQUIRED_DEFINITIONS ${CMAKE_CXX11_STANDARD_COMPILE_OPTION})
before
check_cxx_source_compiles(...)

but what if there were other flags etc...
(0037757)
Laurent Demailly   
2015-01-20 14:05   
I realized it seems internally check compiler flags calls CHECK_CXX_SOURCE_COMPILES but I think the "public" version (or a new function) should use all the flags that other CXX files would get

I also have a related (faq?) issue about check_library_exists() using c and not c++ - any way to make it use c++ ?

and (maybe I should ask in seperate issue or email) : why do I must list C CXX in my pure c++ project (if I remove C things fail - I would think cmake should switch to use c++ for everything when the project is CXX ? instead of having some macros that have _cxx and some that only exist with C)
(0037760)
Brad King   
2015-01-21 08:29   
Re 0015361:0037757: For basic projects enabling just CXX is enough for a pure C++ project. However, as you point out check macros like check_library_exists assume C is enabled, so C must be enabled to use them. Many such check macros were written before we had separate C and CXX language enabling capabilities.

As this issue records the check macros need to be taught more about the CXX_STANDARD levels and other information about language variants and flags. The language standard levels and "Compile Features" interfaces are all brand new so not everything has been updated to support them.
(0039119)
Roman80   
2015-07-10 01:12   
I can reproduce the problem on Mac OS 10.10.x too.

The current workaround "for me" is, to set the CMAKE_CXX_FLAGS manually before the check_cxx_source_compiles() calls like:

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

But then I must maintain two places, the CMAKE_CXX_FLAGS and:

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED on)
(0039292)
Laurent Demailly   
2015-08-17 20:02   
ping ?
my temp workaround makes basic thing like

check_function_exists(open HAS_OPEN)

fail

any idea btw to get verbose / details on what cmake did / why it didn't find something ?
(0039293)
Laurent Demailly   
2015-08-17 20:24   
found where to look for errors:

CMakeFiles/CMakeError.log has



error: invalid argument '-std=c++11' not allowed with 'C/ObjC'

as a result for check_function_exists()
(0042701)
Kitware Robot   
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.