parse command line options outside of main()?

[cdwijs]

Hi All,
I am writing a program that does command line parsing. For now the lines that deal with this are in main.cpp, in the constructor. I would like to move this to it's own function, so re-using should be easier, and the function will have less lines. I encounter the following obstacles in my attempt:
->QCommandLineParser requires access to argc and *argv[], so I have to pass those to my function. This is not a big problem, I can just give them as arguments.
->QCommandLineParser requires access to the QCoreApplication instance. In a new empty Qt console application, this is a local variable. I think it's not a good idea to define this variable outside the main constructor.
Is there a solution to break up the main function into smaller functions?
My versions:
Windows 7 enterprise SP1 64 bit
Qt Creator 3.6.0 Based on Qt 5.5.1 (MSVC 2013, 32 bit)
QT5.5, mingw492_32
Cheers,
Cedric

[kshegunov]

Hello,

->QCommandLineParser requires access to argc and *argv[], so I have to pass those to my function. This is not a big problem, I can just give them as arguments.
->QCommandLineParser requires access to the QCoreApplication instance. In a new empty Qt console application, this is a local variable. I think it's not a good idea to define

It requires neither of those. It requires a list of strings (QStringList) containing the command line (application path + arguments).

outside the main constructor.

The main constructor?

[cdwijs]

Hi kshegunov,
Thanks for your quick reply. I have made a minimal program that works:

#include <QCoreApplication>
#include <QCommandLineParser>
#include <QDebug>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QCommandLineParser parser;
    parser.setApplicationDescription("Explaining text");
    parser.addHelpOption();

    //An option with a value
    QCommandLineOption targetDirectoryOption(QStringList() << "t" << "target-directory",
            QCoreApplication::translate("main", "Copy all source files into <directory>."),
            QCoreApplication::translate("main", "directory"));
    parser.addOption(targetDirectoryOption);
    // Process the actual command line arguments given by the user
    parser.process(a);

    QString target = parser.value(targetDirectoryOption);
    qDebug()<<target;

    return a.exec();
}

This version gives the following error when I uncomment
parser.process(a);
error: 'a' was not declared in this scope
Without this line, I get the following run-time errors:
QCommandLineParser: call process() or parse() before value
QCommandLineParser: call process() or parse() before values

#include <QCoreApplication>
#include <QCommandLineParser>
#include <QDebug>

void parseCommandLine();

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    parseCommandLine();
    return a.exec();
}

void parseCommandLine()
{
    QCommandLineParser parser;
    parser.setApplicationDescription("Explaining text");
    parser.addHelpOption();

    //An option with a value
    QCommandLineOption targetDirectoryOption(QStringList() << "t" << "target-directory",
            QCoreApplication::translate("main", "Copy all source files into <directory>."),
            QCoreApplication::translate("main", "directory"));
    parser.addOption(targetDirectoryOption);
    // Process the actual command line arguments given by the user
    //parser.process(a); //error: 'a' was not declared in this scope

    QString target = parser.value(targetDirectoryOption);
    qDebug()<<target;
}

I see the following page has an example, that passes a reference to the parser object.
http://doc.qt.io/qt-5/qcommandlineparser.html
I will try that and report back.
Cheers,
Cedric

[cdwijs]

Hi All,
The following works, so my problem is fixed:

#include <QCoreApplication>
#include <QCommandLineParser>
#include <QDebug>

void parseCommandLine(QCommandLineParser &parser);

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QCommandLineParser parser;
    parseCommandLine(parser);
    return a.exec();
}

void parseCommandLine(QCommandLineParser &parser)
{

    parser.setApplicationDescription("Explaining text");
    parser.addHelpOption();

    //An option with a value
    QCommandLineOption targetDirectoryOption(QStringList() << "t" << "target-directory",
            QCoreApplication::translate("main", "Copy all source files into <directory>."),
            QCoreApplication::translate("main", "directory"));
    parser.addOption(targetDirectoryOption);
    // Process the actual command line arguments given by the user
    parser.process(QCoreApplication::arguments());

    QString target = parser.value(targetDirectoryOption);
    qDebug()<<target;
}

Cheers,
Cedric

[VRonin]

also you can easily get the application instance wherever you want using QCoreApplication::instance() static method

[kshegunov]

@cdwijs
Why not pass the actual arguments instead? E.g:

#include <QCoreApplication>
#include <QCommandLineParser>
#include <QDebug>

void parseCommandLine(const QStringList &);

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

    parseCommandLine(QCoreApplication::arguments());

    return QCoreApplication::exec();
}

void parseCommandLine(const QStringList & arguments)
{
    QCommandLineParser parser;
    // ...
    parser.process(arguments); //< I advise QCommandLineParser::parse instead, since it doesn't call exit() on error.
    // ...
}

[cdwijs]

@kshegunov
QStringList is new for me, that's the reason :-)
Your solution is clean, as the main function now doesn't have to know anything about parsing.
Now I can create a class that does nothing more than parsing the strings, and put them into a QSettings object.

Thanks for your help,
Cedric

[kshegunov]

You're welcome. Happy coding!