"CONFIG += c++11" in .pro however "-std=gnu++0x" in Compile output

fxch

Hi,

My .pro has the CONFIG += c++11 statement however compile output shows the flag -std=gnu++0x.
I'd like to know if it's correct and if the compiler actually is compiling c++11 or c++0x. Thank you.
Alt text

SGaist

Hi and welcome to devnet,

Did you re-run qmake after adding c++11 to CONFIG ? Also, what version of MinGW are you using ?

fxch

@SGaist Hi,

I entered in build folder and deleted all files :

$ cd ~/cpp/build-untitled-Desktop_Qt_5_6_0_GCC_64bit-Debug/
$ rm *

After clicked Build >> Build All and the result was:

19:47:01: Running steps for project untitled...
19:47:01: Starting: "/home/christiano/Qt/5.6/gcc_64/bin/qmake" /home/christiano/cpp/untitled/untitled.pro -r -spec linux-g++ CONFIG+=debug CONFIG+=qml_debug
19:47:01: The process "/home/christiano/Qt/5.6/gcc_64/bin/qmake" exited normally.
19:47:01: Starting: "/usr/bin/make" 
g++ -c -pipe -g -std=gnu++0x -Wall -W -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_CORE_LIB -I../untitled -I. -I../../Qt/5.6/gcc_64/include -I../../Qt/5.6/gcc_64/include/QtCore -I. -I../../Qt/5.6/gcc_64/mkspecs/linux-g++ -o Vector.o ../untitled/Vector.cpp
g++ -c -pipe -g -std=gnu++0x -Wall -W -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_CORE_LIB -I../untitled -I. -I../../Qt/5.6/gcc_64/include -I../../Qt/5.6/gcc_64/include/QtCore -I. -I../../Qt/5.6/gcc_64/mkspecs/linux-g++ -o main.o ../untitled/main.cpp
g++ -Wl,-z,origin -Wl,-rpath,\$ORIGIN -Wl,-rpath,/home/christiano/Qt/5.6/gcc_64/lib -o untitled Vector.o main.o   -L/home/christiano/Qt/5.6/gcc_64/lib -lQt5Core -lpthread 
19:47:03: The process "/usr/bin/make" exited normally.
19:47:03: Elapsed time: 00:02.

I am using Linux RHEL 7.2 and Qt Creator 3.6.1.

Paul Colby

Would you mind showing the output of:

cat /home/christiano/cpp/untitled/untitled.pro

I know it should be the same as the image you included above, but I'd like to be able to cut-and-paste it into a file to test locally.

Thanks :)

fxch

@SGaist @Paul-Colby Hi,
I think I understood:

$ man g++

...
-std=
Determine the language standard. This option is currently only supported when compiling C or C++. The compiler can accept several base standards, such as c90 or c++98, and GNU dialects of those standards, such as gnu90 or gnu++98. When a base standard is specified, the compiler accepts all programs following that standard plus those using GNU extensions that do not contradict it. For example, -std=c90 turns off certain features of GCC that are incompatible with ISO C90, such as the "asm" and "typeof" keywords, but not other GNU extensions that do not have a meaning in ISO C90, such as omitting the middle term of a "?:" expression. On the other hand, when a GNU dialect of a standard is specified, all features supported by the compiler are enabled, even when those features change the meaning of the base standard. As a result, some strict-conforming programs may be rejected. The particular standard is used by -Wpedantic to identify which features are GNU extensions given that version of the standard. For example -std=gnu90 -Wpedantic warns about C++ style // comments, while -std=gnu99 -Wpedantic does not.
A value for this option must be provided; possible values are
...
c++11
c++0x
The 2011 ISO C++ standard plus amendments. Support for C++11 is still experimental, and may change in incompatible ways in future releases. The name c++0x is deprecated.
...
gnu++11
gnu++0x
GNU dialect of -std=c++11. Support for C++11 is still experimental, and may change in incompatible ways in future releases. The name gnu++0x is deprecated.

Therefore gnu++0x, as well as gnu++11, are GNU dialects of the same ISO C++ standard: the 2011; the first being a std value deprecated.

Anyway, below the .pro


QT += core
QT -= gui

CONFIG += c++11


TARGET = untitled
CONFIG += console
CONFIG -= app_bundle

TEMPLATE = app

SOURCES += \
    Vector.cpp \
    main.cpp

HEADERS += \
    Vector.h

Thank you!

Paul Colby

@fxch said:

Therefore gnu++0x, as well as gnu++11, are GNU dialects of the same ISO C++ standard: the 2011; the first being a std value deprecated.

Yep, looks like you are correct.

qtbase/mkspecs/common/g++-base.conf [Qt 5.6]:

QMAKE_CXXFLAGS_CXX11    = -std=c++0x
QMAKE_CXXFLAGS_CXX14    = -std=c++1y
QMAKE_CXXFLAGS_CXX1Z    = -std=c++1z
QMAKE_CXXFLAGS_GNUCXX11 = -std=gnu++0x
QMAKE_CXXFLAGS_GNUCXX14 = -std=gnu++1y
QMAKE_CXXFLAGS_GNUCXX1Z = -std=gnu++1z

qtbase/mkspecs/common/g++-base.conf [Qt 5.7]:

QMAKE_CXXFLAGS_CXX11    = -std=c++11
QMAKE_CXXFLAGS_CXX14    = -std=c++1y
QMAKE_CXXFLAGS_CXX1Z    = -std=c++1z
QMAKE_CXXFLAGS_GNUCXX11 = -std=gnu++11
QMAKE_CXXFLAGS_GNUCXX14 = -std=gnu++1y
QMAKE_CXXFLAGS_GNUCXX1Z = -std=gnu++1z

Cheers.

_PIB

@fxch this bugs me as well. Qmake puts GNU dialect for whatever reason both with CONFIG += c++11 and without it.

I have my mkspec modified so I noticed that QMAKE_CXXFLAGS_GNUCXX11 is used by Qmake for whatever reason (this whole variable is fed to compiler).

Of course it does not matter largely but I would rather like to have control over dialect used.

QT v5.8.0

_PIB

Convenient solution was:

CONFIG+= strict_c++ c++11

This would disable GNU dialect before C++11.prf was removed from source tree:
https://git.merproject.org/mer-core/qtbase/blob/041fae00351164fbd72763e4bd947fdeb9956a5d/mkspecs/features/c++11.prf

So, now you can only disable gnu extensions by modifying mkspec file.