Development/Tutorials/CommandLineArguments

Command line arguments

Tutorial Series	Beginner Tutorial
Previous	Tutorial 4 - Loading and saving
What's Next	n/a
Further Reading	n/a

Abstract

Now that we have a text editor that can open and save files. We will now make the editor act more like a desktop application by enabling it to open files from command line arguments or even using Open with from within Dolphin.

The Code

main.cpp

#include <cstdlib>
 
#include <QApplication>
#include <QCommandLineParser>
#include <QUrl>
#include <QDir>

#include <KAboutData>
#include <KLocalizedString>

#include "mainwindow.h"
 
int main (int argc, char *argv[])
{
    QApplication app(argc, argv);
    
    KLocalizedString::setApplicationDomain("tutorial5");
    
    KAboutData aboutData(
                         // The program name used internally. (componentName)
                         QStringLiteral("tutorial5"),
                         // A displayable program name string. (displayName)
                         i18n("Tutorial 5"),
                         // The program version string. (version)
                         QStringLiteral("1.0"),
                         // Short description of what the app does. (shortDescription)
                         i18n("A simple text area which can load and save."),
                         // The license this code is released under
                         KAboutLicense::GPL,
                         // Copyright Statement (copyrightStatement = QString())
                         i18n("(c) 2015"),
                         // Optional text shown in the About box.
                         // Can contain any information desired. (otherText)
                         i18n("Some text..."),
                         // The program homepage string. (homePageAddress = QString())
                         QStringLiteral("http://example.com/"),
                         // The bug report email address
                         // (bugsEmailAddress = QLatin1String("[email protected]")
                         QStringLiteral("[email protected]"));
    
    aboutData.addAuthor(i18n("Name"), i18n("Task"), QStringLiteral("[email protected]"),
                        QStringLiteral("http://your.website.com"), QStringLiteral("OSC Username"));
    
    KAboutData::setApplicationData(aboutData);
 
    QCommandLineParser parser;
    aboutData.setupCommandLine(&parser);
    parser.addPositionalArgument(QStringLiteral("file"), i18n("Document to open"));
    
    parser.process(app);
    aboutData.processCommandLine(&parser);
    
    MainWindow* window = new MainWindow();
    window->show();
    
    if (parser.positionalArguments().count() > 0)
    {
        window->openFile(QUrl::fromUserInput(parser.positionalArguments().at(0), QDir::currentPath()));
    }
    
    return app.exec();
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <KXmlGuiWindow>

class KTextEdit;
class KJob;
 
class MainWindow : public KXmlGuiWindow
{
    Q_OBJECT
    
  public:
    explicit MainWindow(QWidget *parent = nullptr);
    void openFile(const QUrl &inputFileName);
 
  private:
    void setupActions();
 
  private slots:
    void newFile();
    void openFile();
    void saveFile();
    void saveFileAs();
    void saveFileAs(const QString &outputFileName);
    
    void downloadFinished(KJob* job);

  private:
    KTextEdit* textArea;
    QString fileName;
};
 
#endif

mainwindow.cpp

#include <QApplication>
#include <QAction>
#include <QSaveFile>
#include <QFileDialog>
#include <QTextStream>
#include <QByteArray>

#include <KTextEdit>
#include <KLocalizedString>
#include <KActionCollection>
#include <KStandardAction>
#include <KMessageBox>
#include <KIO/Job>

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent) : KXmlGuiWindow(parent), fileName(QString())
{
  textArea = new KTextEdit();
  setCentralWidget(textArea);
  
  setupActions();
}

void MainWindow::setupActions()
{
    QAction* clearAction = new QAction(this);
    clearAction->setText(i18n("&Clear"));
    clearAction->setIcon(QIcon::fromTheme("document-new"));
    actionCollection()->setDefaultShortcut(clearAction, Qt::CTRL + Qt::Key_W);
    actionCollection()->addAction("clear", clearAction);
    connect(clearAction, SIGNAL(triggered(bool)), textArea, SLOT(clear()));
    
    KStandardAction::quit(qApp, SLOT(quit()), actionCollection());
    
    KStandardAction::open(this, SLOT(openFile()), actionCollection());
 
    KStandardAction::save(this, SLOT(saveFile()), actionCollection());
 
    KStandardAction::saveAs(this, SLOT(saveFileAs()), actionCollection());
 
    KStandardAction::openNew(this, SLOT(newFile()), actionCollection());
    
    setupGUI(Default, "tutorial5ui.rc");
}

void MainWindow::newFile()
{
    fileName.clear();
    textArea->clear();
}

void MainWindow::saveFileAs(const QString &outputFileName)
{
    if (!outputFileName.isNull())
    {
        QSaveFile file(outputFileName);
        file.open(QIODevice::WriteOnly);
        
        QByteArray outputByteArray;
        outputByteArray.append(textArea->toPlainText().toUtf8());
        file.write(outputByteArray);
        file.commit();

        fileName = outputFileName;
    }
}

void MainWindow::saveFileAs()
{
    saveFileAs(QFileDialog::getSaveFileName(this, i18n("Save File As")));
}

void MainWindow::saveFile()
{
    if (!fileName.isEmpty())
    {
        saveFileAs(fileName);
    }
    else
    {
        saveFileAs();
    }
}


void MainWindow::openFile()
{
    openFile(QFileDialog::getOpenFileUrl(this, i18n("Open File")));
}
    
void MainWindow::openFile(const QUrl &inputFileName)
{
    if (!inputFileName.isEmpty())
    {
        KIO::Job* job = KIO::storedGet(inputFileName);
        fileName = inputFileName.toLocalFile();

        connect(job, SIGNAL(result(KJob*)), this, SLOT(downloadFinished(KJob*)));
        
        job->exec();
    }
}

void MainWindow::downloadFinished(KJob* job)
{
    if (job->error())
    {
        KMessageBox::error(this, job->errorString());
        fileName.clear();
        return;
    }
    
    KIO::StoredTransferJob* storedJob = (KIO::StoredTransferJob*)job;
    textArea->setPlainText(QTextStream(storedJob->data(), QIODevice::ReadOnly).readAll());
}

tutorial5ui.rc

<?xml version="1.0" encoding="UTF-8"?>
<gui name="tutorial5"
     version="1"
     xmlns="http://www.kde.org/standards/kxmlgui/1.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.kde.org/standards/kxmlgui/1.0
                         http://www.kde.org/standards/kxmlgui/1.0/kxmlgui.xsd" >
 
  <MenuBar>
    <Menu name="file" >
      <Action name="clear" />
    </Menu>
  </MenuBar>
 
  <ToolBar name="mainToolBar" >
    <text>Main Toolbar</text>
    <Action name="clear" />
  </ToolBar>
 
</gui>

Explanation

mainwindow.h

Here we have done nothing but add a new openFile function which takes a QUrl. Again, we use a QUrl instead of a QString so that we can also work with remote files as if they were local.

void openFile(const QUrl &inputFileName);

mainwindow.cpp

There's no new code here, only rearranging. Everything from void openFile() has been moved into void openFile(const QUrl &inputFileName) except the call to QFileDialog::getOpenFileUrl().

This way, we can call openFile() if we want to display a dialog, or we can call openFile(QUrl) if we know the name of the file already. Which will be the case when we feed the file name through the command line.

main.cpp

This is where all the QCommandLineParser magic happens. In previous examples, we only used the class to feed QApplication the necessary data for using flags like --version or --author. Now we actually get to use it to process command line arguments.

First, we tell QCommandLineParser that we want to add a new positional arguments. In a nutshell, these are arguments that are not options. -h or --version are options, file is an argument.

parser.addPositionalArgument(QStringLiteral("file"), i18n("Document to open"));

Later on, we start processing positional arguments, but only if there is one. Otherwise, we proceed as usual. In our case we can only open one file at a time, so only the first file is of interest to us. We call the openFile() function and feed it the URL of the file we want to open, whether it is a local file like $HOME/foo or a remote one like ftp.mydomain.com/bar. We use the overloaded form of QUrl::fromUserInput() in order to set the current path. This is needed in order to work with relative paths like "../baz".

if (parser.positionalArguments().count() > 0)
{
    window->openFile(QUrl::fromUserInput(parser.positionalArguments().at(0), QDir::currentPath()));
}

Make, Install and Run

CMakeLists.txt

cmake_minimum_required(VERSION 3.0)

project (tutorial5)

set(QT_MIN_VERSION "5.3.0")
set(KF5_MIN_VERSION "5.2.0")

find_package(ECM 1.0.0 REQUIRED NO_MODULE)
set(CMAKE_MODULE_PATH ${ECM_MODULE_PATH} ${CMAKE_CURRENT_SOURCE_DIR}/cmake)

include(KDEInstallDirs)
include(KDECMakeSettings)
include(KDECompilerSettings NO_POLICY_SCOPE)
include(FeatureSummary)

find_package(Qt5 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS 
    Core    # QCommandLineParser, QStringLiteral, QSaveFile, QTextStream, QByteArray
    Widgets # QApplication, QAction, QFileDialog
)

find_package(KF5 ${KF5_MIN_VERSION} REQUIRED COMPONENTS
    CoreAddons      # KAboutData
    I18n            # KLocalizedString
    XmlGui          # KXmlGuiWindow, KActionCollection
    TextWidgets     # KTextEdit
    ConfigWidgets   # KStandardActions
    WidgetsAddons   # KMessageBox
    KIO             # KIO
)
    
feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)
    
set(tutorial5_SRCS main.cpp mainwindow.cpp)

add_executable(tutorial5 ${tutorial5_SRCS})

target_link_libraries(tutorial5
    Qt5::Widgets
    KF5::CoreAddons
    KF5::I18n
    KF5::XmlGui
    KF5::TextWidgets
    KF5::ConfigWidgets
    KF5::WidgetsAddons
    KF5::KIOCore
)

install(TARGETS tutorial5  ${KDE_INSTALL_TARGETS_DEFAULT_ARGS})

install(FILES tutorial5ui.rc DESTINATION ${KDE_INSTALL_KXMLGUI5DIR}/tutorial5)

With this file, the tutorial can built and run in the same way as tutorial 3 and 4. For more information, see tutorial 3.

mkdir build && cd build
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME
make install
XDG_DATA_DIRS=$HOME/share:$XDG_DATA_DIRS $HOME/bin/tutorial5