Compiling with gcc fails if using lambda function for QObject::connect()

Question

This Code compiles without any problems Qt5.2.0 MSVC2012:

#include <QCoreApplication>
#include <QObject>
#include <QTimer>
#include <QDebug>

int main(int argc, char *argv[])
{
    QTimer timer;
    QCoreApplication a(argc, argv);

    QObject::connect(&timer, &QTimer::timeout,
            [=] () {
       qDebug() << Q_FUNC_INFO;
    });

    timer.start(1000);

    return a.exec();
}

But if I try to compile it with Qt5.2.0 with gcc I get this errors:

../_test_gccLambda/main.cpp: In function 'int main(int, char**)': ../_test_gccLambda/main.cpp:14:5: warning: lambda expressions only available with -std=c++11 or -std=gnu++11 [enabled by default] }); ^ ../_test_gccLambda/main.cpp:14:6: error: no matching function for call to 'QObject::connect(QTimer*, void (QTimer::)(QTimer::QPrivateSignal), main(int, char*)::__lambda0)' }); ^ ../_test_gccLambda/main.cpp:14:6: note: candidates are: In file included from ../../Qt5/5.2.0/gcc_64/include/QtCore/qcoreapplication.h:48:0, from ../../Qt5/5.2.0/gcc_64/include/QtCore/QCoreApplication:1, from ../_test_gccLambda/main.cpp:1: ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:198:36: note: static QMetaObject::Connection QObject::connect(const QObject*, const char*, const QObject*, const char*, Qt::ConnectionType) static QMetaObject::Connection connect(const QObject *sender, const char *signal, ^ ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:198:36: note: candidate expects 5 arguments, 3 provided ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:201:36: note: static QMetaObject::Connection QObject::connect(const QObject*, const QMetaMethod&, const QObject*, const QMetaMethod&, Qt::ConnectionType) static QMetaObject::Connection connect(const QObject *sender, const QMetaMethod &signal, ^ ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:201:36: note: candidate expects 5 arguments, 3 provided ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:479:32: note: QMetaObject::Connection QObject::connect(const QObject*, const char*, const char*, Qt::ConnectionType) const inline QMetaObject::Connection QObject::connect(const QObject *asender, const char *asignal, ^ ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:479:32: note: no known conversion for argument 2 from 'void (QTimer::)(QTimer::QPrivateSignal)' to 'const char' ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:215:43: note: template static QMetaObject::Connection QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, const typename QtPrivate::FunctionPointer::Object*, Func2, Qt::ConnectionType) static inline QMetaObject::Connection connect(const typename QtPrivate::FunctionPointer::Object *sender, Func1 signal, ^ ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:215:43: note: template argument deduction/substitution failed: ../_test_gccLambda/main.cpp:14:6: note: mismatched types 'const typename QtPrivate::FunctionPointer::Object*' and 'main(int, char**)::__lambda0' }); ^ In file included from ../../Qt5/5.2.0/gcc_64/include/QtCore/qcoreapplication.h:48:0, from ../../Qt5/5.2.0/gcc_64/include/QtCore/QCoreApplication:1, from ../_test_gccLambda/main.cpp:1: ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:247:13: note: template static typename QtPrivate::QEnableIf<((int)(QtPrivate::FunctionPointer::ArgumentCount) >= 0), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, Func2) connect(const typename QtPrivate::FunctionPointer::Object *sender, Func1 signal, Func2 slot) ^ ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:247:13: note: template argument deduction/substitution failed: ../_test_gccLambda/main.cpp: In substitution of 'template static typename QtPrivate::QEnableIf<((int)(QtPrivate::FunctionPointer::ArgumentCount) >= 0), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, Func2) [with Func1 = void (QTimer::)(QTimer::QPrivateSignal); Func2 = main(int, char*)::__lambda0]': ../_test_gccLambda/main.cpp:14:6: required from here ../_test_gccLambda/main.cpp:14:6: error: template argument for 'template static typename QtPrivate::QEnableIf<((int)(QtPrivate::FunctionPointer::ArgumentCount) >= 0), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, Func2)' uses local type 'main(int, char**)::__lambda0' }); ^ ../_test_gccLambda/main.cpp:14:6: error: trying to instantiate 'template static typename QtPrivate::QEnableIf<((int)(QtPrivate::FunctionPointer::ArgumentCount) >= 0), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, Func2)' In file included from ../../Qt5/5.2.0/gcc_64/include/QtCore/qcoreapplication.h:48:0, from ../../Qt5/5.2.0/gcc_64/include/QtCore/QCoreApplication:1, from ../_test_gccLambda/main.cpp:1: ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:256:13: note: template static typename QtPrivate::QEnableIf<(((int)(QtPrivate::FunctionPointer::ArgumentCount) >= 0) && (! QtPrivate::FunctionPointer::IsPointerToMemberFunction)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) connect(const typename QtPrivate::FunctionPointer::Object *sender, Func1 signal, const QObject *context, Func2 slot, ^ ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:256:13: note: template argument deduction/substitution failed: ../_test_gccLambda/main.cpp:14:6: note: cannot convert 'main(int, char**)::__lambda0{}' (type 'main(int, char**)::__lambda0') to type 'const QObject*' }); ^ In file included from ../../Qt5/5.2.0/gcc_64/include/QtCore/qcoreapplication.h:48:0, from ../../Qt5/5.2.0/gcc_64/include/QtCore/QCoreApplication:1, from ../_test_gccLambda/main.cpp:1: ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:287:13: note: template static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, Func2) connect(const typename QtPrivate::FunctionPointer::Object *sender, Func1 signal, Func2 slot) ^ ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:287:13: note: template argument deduction/substitution failed: ../_test_gccLambda/main.cpp: In substitution of 'template static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, Func2) [with Func1 = void (QTimer::)(QTimer::QPrivateSignal); Func2 = main(int, char*)::__lambda0]': ../_test_gccLambda/main.cpp:14:6: required from here ../_test_gccLambda/main.cpp:14:6: error: template argument for 'template static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, Func2)' uses local type 'main(int, char**)::__lambda0' }); ^ ../_test_gccLambda/main.cpp:14:6: error: trying to instantiate 'template static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, Func2)' In file included from ../../Qt5/5.2.0/gcc_64/include/QtCore/qcoreapplication.h:48:0, from ../../Qt5/5.2.0/gcc_64/include/QtCore/QCoreApplication:1, from ../_test_gccLambda/main.cpp:1: ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:295:13: note: template static typename QtPrivate::QEnableIf<(QtPrivate::FunctionPointer::ArgumentCount == (-1)), QMetaObject::Connection>::Type QObject::connect(const typename QtPrivate::FunctionPointer::Object*, Func1, const QObject*, Func2, Qt::ConnectionType) connect(const typename QtPrivate::FunctionPointer::Object *sender, Func1 signal, const QObject *context, Func2 slot, ^ ../../Qt5/5.2.0/gcc_64/include/QtCore/qobject.h:295:13: note: template argument deduction/substitution failed: ../_test_gccLambda/main.cpp:14:6: note: cannot convert 'main(int, char**)::__lambda0{}' (type 'main(int, char**)::__lambda0') to type 'const QObject*' }); ^ make: * [main.o] Error 1 16:53:24: The process "/usr/bin/make" exited with code 2. Error while building/deploying project _test_gccLambda (kit: Desktop Qt 5.2.0 GCC 64bit) When executing step 'Make' 16:53:24: Elapsed time: 00:02.

Where is the problem?

compile with -std=c++11 mode. see http://stackoverflow.com/questions/17299139/building-qt-project-for-c11-standard — Khurshid, Feb 10 '14 at 16:11

score 1 · Answer 1 · answered Oct 31 '17 at 14:38

1

as answered in comments, use -std=c++11 to have it compiles with gcc

answered Oct 31 '17 at 14:38

sandwood

2,038
20
38

I'm not sure a question that demonstrates such a lack of basic reading comprehension or language awareness needs an answer. But while you're posting someone else's comment as an answer, you could at least explain everything that is required (i.e. including the QMake config in some cases), and why. – underscore_d Oct 31 '17 at 14:43
To be honnest I have tried to follow the procedure suggested in meta stack overflow; when the response is on the comments (gives answer and put community wiki). I agree with you and indeed I would rather like to be able to report this question as too lame but it seems there is no such flag. – sandwood Oct 31 '17 at 14:48

Compiling with gcc fails if using lambda function for QObject::connect()

1 Answers1