使用clang的QT标头中的错误

Question

Questions:

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My question is thus: How do I build my QT project without turning off warnings altogether (or having to sort through a million purposeless ones to find my own)? Can I suppress warnings for just the QT headers?

Details:

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Issue

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A number of months ago, I started a QT project in QT-Creator. At the time I was using gcc 4.6. After a bit other priorities asserted themselves and I found myself without time to work on the project until now. In the interim I switched to using clang. When I configured my QT project to use clang -- which project compiled without warnings in g++ -- it generated some 263 warnings all within the QT headers themselves. Mostly sign-conversion and unreachable-code.

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Attempts

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To try and get around this I added -isystem /path/to/QT/include/dir based on this entry in the Clang User Manual , but it did not seem to affect anything. Though I am not certain, I think it is because my code #include 's the QT headers by name, not by directory. While the solution to that might be to manually list every single QT header used (have not tried), it would mean I would have to update it every time I upgraded QT or used a new header. Surely there is a better solution.

As requested here is the actual compile command being executed:

clang++ -c -pipe -Qunused-arguments -Weverything -cxx-isystem /path/to/qt/4.8.3/include/ -g -D_REENTRANT -DQT_NO_KEYWORDS -DQT_SHARED -I/path/to/qt/x86_64/4.8.3/mkspecs/unsupported/linux-clang -I. -I.moc -I.ui -I/path/to/qt/4.8.3/include/ -o .obj/main.o main.cpp

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Specs

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I am using:

• Linux 3.2.0-40-generic #64-Ubuntu SMP x86_64 GNU/Linux
  • Though others on my team use Windows
• QT creator 2.6.2
• QT 4.8.3
• clang version 3.2 (trunk 165250) (llvm/trunk 165249)
  • Target: x86_64-unknown-linux-gnu

Answer 1

I will answer my own question because, as it turns out, it is a specific environmental quirk in this case.

I have two copies of the QT libraries on my dev machine, one system-wide and one project specific (included in the VCS). The project libraries do not have qmake included, so I used my system qmake, which appended a different path than I was including in my -isystem specifications. To solve this, I added

QMAKE_INCDIR_QT = 

to qmake.conf (in qt/mkspecs/unsupported/linux-clang/)

Since someone else on the project had fanangled qmake into using the project libraries everywhere else.

Answer 2

For those who stumble upon this question with a more general problem than the author. Try inserting:

LIBS_USED_FOR_QT = QtCore QtSql QtMultimediaWidgets QtSensors QtSvg QtXml QtPrintSupport QtWidgets QtQuick QtQml QtPositioning QtGui QtWebKitWidgets
for(somelib, $$list($$LIBS_USED_FOR_QT)) {
    QMAKE_CXXFLAGS += -isystem $$(QTDIR)/lib/$${somelib}.framework/Versions/5/Headers/
    QMAKE_CXXFLAGS += -isystem $$(QTDIR)/lib/$${somelib}.framework/Headers/
}

in your .pro file. Addtionally avoid includes like #include <QtCore/QtCore> writing #include <QtCore> instead

This tamed qt quite efficiently for me.

see also this source