Question

The following snippet is from a little app I wrote using the Qt framework. The idea is that the app can be run in batch mode (i.e. called by a script) or can be run interactively.

It is important therefore, that I am able to parse command line arguments in order to know which mode in which to run etc.

[Edit]

I am debugging using Qt Creator 1.3.1 on Ubuntu Karmic. The arguments are passed in the normal way (i.e. by adding them via the ‘Project’ settings in the Qt Creator IDE).

When I run the app, it appears that the arguments are not being passed to the application. The code below, is a snippet of my main() function.

int main(int argc, char *argv[])
{
    //Q_INIT_RESOURCE(application);

    try {
        QApplication the_app(argc, argv);

        //trying to get the arguments into a list    
        QStringList cmdline_args = QCoreApplication::arguments();

        // Code continues ...
    }
    catch (const MyCustomException &e) { return 1; }

    return 0;
}

[Update]

I have identified the problem – for some reason, although argc is correct, the elements of argv are empty strings.

I put this little code snippet to print out the argv items – and was horrified to see that they were all empty.

for (int i=0; i< argc; i++){
    std::string s(argv[i]); //required so I can see the damn variable in the debugger
    std::cout << s << std::endl;
}

Does anyone know how I can retrieve the command line args in my application?

Answer 1

If your argc and argv are good, I’m surprised this would be possible as QApplication::arguments() is extremely simple. Note the source code. Filtering the #ifdefs for Linux, it’s just:

QStringList QCoreApplication::arguments()
{
    QStringList list;
    if (!self) {
        qWarning("QCoreApplication::arguments: Please instantiate the QApplication object first");
        return list;
    }
    const int ac = self->d_func()->argc;
    char ** const av = self->d_func()->argv;
    for (int a = 0; a < ac; ++a) {
        list << QString::fromLocal8Bit(av[a]);
    }
    return list;
}

That’s all you’ve got. There’s a Unicode caveat which I would not think would apply to Karmic:

“On Unix, this list is built from the argc and argv parameters passed to the constructor in the main() function. The string-data in argv is interpreted using QString::fromLocal8Bit(); hence it is not possible to pass, for example, Japanese command line arguments on a system that runs in a Latin1 locale. Most modern Unix systems do not have this limitation, as they are Unicode-based.”

You might try a copy of that code against your argc and argv directly and see what happens.