QCommandLineParser Class

In practice, additional error checking needs to be performed on the positional arguments and option values. For example, ranges of numbers should be checked.

It is then advisable to introduce a function to do the command line parsing which takes a struct or class receiving the option values returning an enumeration representing the result. The dnslookup example of the QtNetwork module illustrates this:

struct DnsQuery
{
    DnsQuery() : type(QDnsLookup::A) {}

    QDnsLookup::Type type;
    QHostAddress nameServer;
    QString name;
};

enum CommandLineParseResult
{
    CommandLineOk,
    CommandLineError,
    CommandLineVersionRequested,
    CommandLineHelpRequested
};

CommandLineParseResult parseCommandLine(QCommandLineParser &parser, DnsQuery *query, QString *errorMessage)
{
    parser.setSingleDashWordOptionMode(QCommandLineParser::ParseAsLongOptions);
    const QCommandLineOption nameServerOption("n", "The name server to use.", "nameserver");
    parser.addOption(nameServerOption);
    const QCommandLineOption typeOption("t", "The lookup type.", "type");
    parser.addOption(typeOption);
    parser.addPositionalArgument("name", "The name to look up.");
    const QCommandLineOption helpOption = parser.addHelpOption();
    const QCommandLineOption versionOption = parser.addVersionOption();

    if (!parser.parse(QCoreApplication::arguments())) {
        *errorMessage = parser.errorText();
        return CommandLineError;
    }

    if (parser.isSet(versionOption))
        return CommandLineVersionRequested;

    if (parser.isSet(helpOption))
        return CommandLineHelpRequested;

    if (parser.isSet(nameServerOption)) {
        const QString nameserver = parser.value(nameServerOption);
        query->nameServer = QHostAddress(nameserver);
        if (query->nameServer.isNull() || query->nameServer.protocol() == QAbstractSocket::UnknownNetworkLayerProtocol) {
            *errorMessage = "Bad nameserver address: " + nameserver;
            return CommandLineError;
        }
    }

    if (parser.isSet(typeOption)) {
        const QString typeParameter = parser.value(typeOption);
        const int type = typeFromParameter(typeParameter.toLower());
        if (type < 0) {
            *errorMessage = "Bad record type: " + typeParameter;
            return CommandLineError;
        }
        query->type = static_cast<QDnsLookup::Type>(type);
    }

    const QStringList positionalArguments = parser.positionalArguments();
    if (positionalArguments.isEmpty()) {
        *errorMessage = "Argument 'name' missing.";
        return CommandLineError;
    }
    if (positionalArguments.size() > 1) {
        *errorMessage = "Several 'name' arguments specified.";
        return CommandLineError;
    }
    query->name = positionalArguments.first();

    return CommandLineOk;
}

In the main function, help should be printed to the standard output if the help option was passed and the application should return the exit code 0.

If an error was detected, the error message should be printed to the standard error output and the application should return an exit code other than 0.

    QCoreApplication::setApplicationVersion(QT_VERSION_STR);
    QCoreApplication::setApplicationName(QCoreApplication::translate("QDnsLookupExample", "DNS Lookup Example"));
    QCommandLineParser parser;
    parser.setApplicationDescription(QCoreApplication::translate("QDnsLookupExample", "An example demonstrating the class QDnsLookup."));
    DnsQuery query;
    QString errorMessage;
    switch (parseCommandLine(parser, &query, &errorMessage)) {
    case CommandLineOk:
        break;
    case CommandLineError:
        fputs(qPrintable(errorMessage), stderr);
        fputs("\n\n", stderr);
        fputs(qPrintable(parser.helpText()), stderr);
        return 1;
    case CommandLineVersionRequested:
        printf("%s %s\n", qPrintable(QCoreApplication::applicationName()),
               qPrintable(QCoreApplication::applicationVersion()));
        return 0;
    case CommandLineHelpRequested:
        parser.showHelp();
        Q_UNREACHABLE();
    }

A special case to consider here are GUI applications on Windows and mobile platforms. These applications may not use the standard output or error channels since the output is either discarded or not accessible.

On Windows, QCommandLineParser uses message boxes to display usage information and errors if no console window can be obtained.

For other platforms, it is recommended to display help texts and error messages using a QMessageBox. To preserve the formatting of the help text, rich text with <pre> elements should be used:

switch (parseCommandLine(parser, &query, &errorMessage)) {
case CommandLineOk:
    break;
case CommandLineError:
    QMessageBox::warning(0, QGuiApplication::applicationDisplayName(),
                         "<html><head/><body><h2>" + errorMessage + "</h2><pre>"
                         + parser.helpText() + "</pre></body></html>");
    return 1;
case CommandLineVersionRequested:
    QMessageBox::information(0, QGuiApplication::applicationDisplayName(),
                             QGuiApplication::applicationDisplayName() + ' '
                             + QCoreApplication::applicationVersion());
    return 0;
case CommandLineHelpRequested:
    QMessageBox::warning(0, QGuiApplication::applicationDisplayName(),
                         "<html><head/><body><pre>"
                         + parser.helpText() + "</pre></body></html>");
    return 0;
}

However, this does not apply to the dnslookup example, because it is a console application.

See also QCommandLineOption, QCoreApplication

This enum describes the way the parser interprets options that occur after positional arguments.

This enum was introduced or modified in Qt 5.6.

See Also▲

This enum describes the way the parser interprets command-line options that use a single dash followed by multiple letters, as as -abc.

See Also▲

Constructs a command line parser object.

Destroys the command line parser object.

Adds the help option (-h, --help and -? on Windows) as well as an option --help-all to include Qt-specific options in the output.

These options are handled automatically by QCommandLineParser.

Remember to use setApplicationDescription to set the application description, which will be displayed when this option is used.

Example:

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    QCoreApplication::setApplicationName("my-copy-program");
    QCoreApplication::setApplicationVersion("1.0");

    QCommandLineParser parser;
    parser.setApplicationDescription("Test helper");
    parser.addHelpOption();
    parser.addVersionOption();
    parser.addPositionalArgument("source", QCoreApplication::translate("main", "Source file to copy."));
    parser.addPositionalArgument("destination", QCoreApplication::translate("main", "Destination directory."));

    // A boolean option with a single name (-p)
    QCommandLineOption showProgressOption("p", QCoreApplication::translate("main", "Show progress during copy"));
    parser.addOption(showProgressOption);

    // A boolean option with multiple names (-f, --force)
    QCommandLineOption forceOption(QStringList() << "f" << "force",
            QCoreApplication::translate("main", "Overwrite existing files."));
    parser.addOption(forceOption);

    // 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(app);

    const QStringList args = parser.positionalArguments();
    // source is args.at(0), destination is args.at(1)

    bool showProgress = parser.isSet(showProgressOption);
    bool force = parser.isSet(forceOption);
    QString targetDir = parser.value(targetDirectoryOption);
    // ...
}

Returns the option instance, which can be used to call isSet().

Adds the option option to look for while parsing.

Returns true if adding the option was successful; otherwise returns false.

Adding the option fails if there is no name attached to the option, or the option has a name that clashes with an option name added before.

Adds the options to look for while parsing. The options are specified by the parameter options.

Returns true if adding all of the options was successful; otherwise returns false.

See the documentation for addOption() for when this function may fail.

This function was introduced in Qt 5.4.

Defines an additional argument to the application, for the benefit of the help text.

The argument name and description will appear under the Arguments: section of the help. If syntax is specified, it will be appended to the Usage line, otherwise the name will be appended.

Example:

// Usage: image-editor file
//
// Arguments:
//   file                  The file to open.
parser.addPositionalArgument("file", QCoreApplication::translate("main", "The file to open."));

// Usage: web-browser [urls...]
//
// Arguments:
//   urls                URLs to open, optionally.
parser.addPositionalArgument("urls", QCoreApplication::translate("main", "URLs to open, optionally."), "[urls...]");

// Usage: cp source destination
//
// Arguments:
//   source                Source file to copy.
//   destination           Destination directory.
parser.addPositionalArgument("source", QCoreApplication::translate("main", "Source file to copy."));
parser.addPositionalArgument("destination", QCoreApplication::translate("main", "Destination directory."));

See Also▲

Adds the -v / --version option, which displays the version string of the application.

This option is handled automatically by QCommandLineParser.

You can set the actual version string by using QCoreApplication::setApplicationVersion().

Returns the option instance, which can be used to call isSet().

Returns the application description set in setApplicationDescription().

See Also▲

Clears the definitions of additional arguments from the help text.

This is only needed for the special case of tools which support multiple commands with different options. Once the actual command has been identified, the options for this command can be defined, and the help text for the command can be adjusted accordingly.

Example:

QCoreApplication app(argc, argv);
QCommandLineParser parser;

parser.addPositionalArgument("command", "The command to execute.");

// Call parse() to find out the positional arguments.
parser.parse(QCoreApplication::arguments());

const QStringList args = parser.positionalArguments();
const QString command = args.isEmpty() ? QString() : args.first();
if (command == "resize") {
    parser.clearPositionalArguments();
    parser.addPositionalArgument("resize", "Resize the object to a new size.", "resize [resize_options]");
    parser.addOption(QCommandLineOption("size", "New size.", "new_size"));
    parser.process(app);
    // ...
}

/*
This code results in context-dependent help:

$ tool --help
Usage: tool command

Arguments:
  command  The command to execute.

$ tool resize --help
Usage: tool resize [resize_options]

Options:
  --size <size>  New size.

Arguments:
  resize         Resize the object to a new size.
*/

Returns a translated error text for the user. This should only be called when parse() returns false.

Returns a string containing the complete help information.

See Also▲

Checks whether the option name was passed to the application.

Returns true if the option name was set, false otherwise.

The name provided can be any long or short name of any option that was added with addOption(). All the options names are treated as being equivalent. If the name is not recognized or that option was not present, false is returned.

Example:

bool verbose = parser.isSet("verbose");

This is an overloaded function.

Checks whether the option was passed to the application.

Returns true if the option was set, false otherwise.

This is the recommended way to check for options with no values.

Example:

QCoreApplication app(argc, argv);
QCommandLineParser parser;
QCommandLineOption verboseOption("verbose");
parser.addOption(verboseOption);
parser.process(app);
bool verbose = parser.isSet(verboseOption);

Returns a list of option names that were found.

This returns a list of all the recognized option names found by the parser, in the order in which they were found. For any long options that were in the form {–option=value}, the value part will have been dropped.

The names in this list do not include the preceding dash characters. Names may appear more than once in this list if they were encountered more than once by the parser.

Any entry in the list can be used with value() or with values() to get any relevant option values.

Parses the command line arguments.

Most programs don't need to call this, a simple call to process() is enough.

parse() is more low-level, and only does the parsing. The application will have to take care of the error handling, using errorText() if parse() returns false. This can be useful for instance to show a graphical error message in graphical programs.

Calling parse() instead of process() can also be useful in order to ignore unknown options temporarily, because more option definitions will be provided later on (depending on one of the arguments), before calling process().

Don't forget that arguments must start with the name of the executable (ignored, though).

Returns false in case of a parse error (unknown option or missing value); returns true otherwise.

See Also▲

Returns a list of positional arguments.

These are all of the arguments that were not recognized as part of an option.

Processes the command line arguments.

In addition to parsing the options (like parse()), this function also handles the builtin options and handles errors.

The builtin options are --version if addVersionOption was called and --help / --help-all if addHelpOption was called.

When invoking one of these options, or when an error happens (for instance an unknown option was passed), the current process will then stop, using the exit() function.

See Also▲

This is an overloaded function.

The command line is obtained from the QCoreApplication instance app.

Sets the application description shown by helpText().

See Also▲

Sets the parsing mode to parsingMode. This must be called before process() or parse().

This function was introduced in Qt 5.6.

Sets the parsing mode to singleDashWordOptionMode. This must be called before process() or parse().

Displays the help information, and exits the application. This is automatically triggered by the –help option, but can also be used to display the help when the user is not invoking the application correctly. The exit code is set to exitCode. It should be set to 0 if the user requested to see the help, and to any other value in case of an error.

See Also▲

Displays the version information from QCoreApplication::applicationVersion(), and exits the application. This is automatically triggered by the –version option, but can also be used to display the version when not using process(). The exit code is set to EXIT_SUCCESS (0).

This function was introduced in Qt 5.4.

See Also▲

Returns a list of unknown option names.

This list will include both long an short name options that were not recognized. For any long options that were in the form {–option=value}, the value part will have been dropped and only the long name is added.

The names in this list do not include the preceding dash characters. Names may appear more than once in this list if they were encountered more than once by the parser.

See Also▲

Returns the option value found for the given option name optionName, or an empty string if not found.

The name provided can be any long or short name of any option that was added with addOption(). All the option names are treated as being equivalent. If the name is not recognized or that option was not present, an empty string is returned.

For options found by the parser, the last value found for that option is returned. If the option wasn't specified on the command line, the default value is returned.

An empty string is returned if the option does not take a value.

See Also▲

This is an overloaded function.

Returns the option value found for the given option, or an empty string if not found.

For options found by the parser, the last value found for that option is returned. If the option wasn't specified on the command line, the default value is returned.

An empty string is returned if the option does not take a value.

See Also▲

Returns a list of option values found for the given option name optionName, or an empty list if not found.

The name provided can be any long or short name of any option that was added with addOption(). All the options names are treated as being equivalent. If the name is not recognized or that option was not present, an empty list is returned.

For options found by the parser, the list will contain an entry for each time the option was encountered by the parser. If the option wasn't specified on the command line, the default values are returned.

An empty list is returned if the option does not take a value.

See Also▲

This is an overloaded function.

Returns a list of option values found for the given option, or an empty list if not found.

For options found by the parser, the list will contain an entry for each time the option was encountered by the parser. If the option wasn't specified on the command line, the default values are returned.

An empty list is returned if the option does not take a value.

See Also▲