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Compilation of Qt5.3.1 on Ubuntu 20.04.1 - QCommandLineParser addVersionOption() Issue

  • Hello,

    I'm trying to compile Qt5.3.1 on Ubuntu 20.04.1 (see this thread for other issues I encountered with foreach loops :

    I could compile OK, but then I discovered another issue at runtime, e.g. 'moc--version' gives "Unknown option 'version'" (the same happens with 'rcc' and 'uic').

    I actually saw many of those messages during compilation:

    QCommandLineParser: option not defined: "version"
    QCommandLineParser: option not defined: "help"

    Although I felt it was probably not normal, I did not look into it as it did not stop me compiling.

    But now, I've been investigating this warnings due to the runtime issue, and here is what I found:

    In main.cpp of moc for example, there are calls to parser.addVersionOption() and parser.addHelpOption() so I looked into those methods in src/corelib/tools/qcommandlineparser.cpp.

    QCommandLineOption QCommandLineParser::addVersionOption()
        QCommandLineOption opt(QStringList() << QStringLiteral("v") << QStringLiteral("version"), tr("Displays version information."));
        d->builtinVersionOption = true;
        return opt;

    We see that addVersionOption() calls addOption(). So I added some debug and here what I found:

    QCommandLineParser: addOptionVersion size = 2       => Correct  size of QStringList (arg 1 of QCommandLineOption)
    QCommandLineParser: addOption optionNames size = 1  => Wrong size of QStringList (option.names.size()) !
    QCommandLineParser: addOption iterating name = v    => So in the loop (replaced by a for loop instead of foreach!), only 'v' gets parsed, not 'version'

    To try, I changed the code to:

    QCommandLineOption opt(QStringList() << QStringLiteral("version"), tr("Displays version information."));

    Then it works fine, and 'moc --version' returns the expected value (+ QCommandLineParser: option not defined: "version" warning disappears of course).

    I'm not able to explain why the QStringList is not passed correctly. So that's where I'm requesting your help trying to understand what's going on !

    I'm compiling using GCC 9.3.0.

    Thanks in advance.

  • Lifetime Qt Champion

    I would take a look in the git history of QCommandLineOption to see if there were fixes/changes to make it work with gcc9

  • Lifetime Qt Champion

    @laurent-c if you really want to keep such an old Qt version (why?), wouldn't it be easier to set up a docker environment for that?


  • @Christian-Ehrlicher That's what I've done, and this line is identical in the latest code. Looking at the git log, I could not find anything relevant.

  • @aha_1980 I'm actually cross-compiling Qt for my embedded device. And I cannot upgrade to latest Qt. I'm cross-compiling for arm (using gcc 4.8 from Linaro toolchain). However, the tools themselves are compiled using the host machine GCC as they have to run on the host machine.

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