Qt Reference Documentation

main.cpp Example File

network/download/main.cpp
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 #include <QCoreApplication>
 #include <QFile>
 #include <QFileInfo>
 #include <QList>
 #include <QNetworkAccessManager>
 #include <QNetworkRequest>
 #include <QNetworkReply>
 #include <QStringList>
 #include <QTimer>
 #include <QUrl>

 #include <stdio.h>

 class DownloadManager: public QObject
 {
     Q_OBJECT
     QNetworkAccessManager manager;
     QList<QNetworkReply *> currentDownloads;

 public:
     DownloadManager();
     void doDownload(const QUrl &url);
     QString saveFileName(const QUrl &url);
     bool saveToDisk(const QString &filename, QIODevice *data);

 public slots:
     void execute();
     void downloadFinished(QNetworkReply *reply);
 };

 DownloadManager::DownloadManager()
 {
     connect(&manager, SIGNAL(finished(QNetworkReply*)),
             SLOT(downloadFinished(QNetworkReply*)));
 }

 void DownloadManager::doDownload(const QUrl &url)
 {
     QNetworkRequest request(url);
     QNetworkReply *reply = manager.get(request);

     currentDownloads.append(reply);
 }

 QString DownloadManager::saveFileName(const QUrl &url)
 {
     QString path = url.path();
     QString basename = QFileInfo(path).fileName();

     if (basename.isEmpty())
         basename = "download";

     if (QFile::exists(basename)) {
         // already exists, don't overwrite
         int i = 0;
         basename += '.';
         while (QFile::exists(basename + QString::number(i)))
             ++i;

         basename += QString::number(i);
     }

     return basename;
 }

 bool DownloadManager::saveToDisk(const QString &filename, QIODevice *data)
 {
     QFile file(filename);
     if (!file.open(QIODevice::WriteOnly)) {
         fprintf(stderr, "Could not open %s for writing: %s\n",
                 qPrintable(filename),
                 qPrintable(file.errorString()));
         return false;
     }

     file.write(data->readAll());
     file.close();

     return true;
 }

 void DownloadManager::execute()
 {
     QStringList args = QCoreApplication::instance()->arguments();
     args.takeFirst();           // skip the first argument, which is the program's name
     if (args.isEmpty()) {
         printf("Qt Download example - downloads all URLs in parallel\n"
                "Usage: download url1 [url2... urlN]\n"
                "\n"
                "Downloads the URLs passed in the command-line to the local directory\n"
                "If the target file already exists, a .0, .1, .2, etc. is appended to\n"
                "differentiate.\n");
         QCoreApplication::instance()->quit();
         return;
     }

     foreach (QString arg, args) {
         QUrl url = QUrl::fromEncoded(arg.toLocal8Bit());
         doDownload(url);
     }
 }

 void DownloadManager::downloadFinished(QNetworkReply *reply)
 {
     QUrl url = reply->url();
     if (reply->error()) {
         fprintf(stderr, "Download of %s failed: %s\n",
                 url.toEncoded().constData(),
                 qPrintable(reply->errorString()));
     } else {
         QString filename = saveFileName(url);
         if (saveToDisk(filename, reply))
             printf("Download of %s succeeded (saved to %s)\n",
                    url.toEncoded().constData(), qPrintable(filename));
     }

     currentDownloads.removeAll(reply);
     reply->deleteLater();

     if (currentDownloads.isEmpty())
         // all downloads finished
         QCoreApplication::instance()->quit();
 }

 int main(int argc, char **argv)
 {
     QCoreApplication app(argc, argv);

     DownloadManager manager;
     QTimer::singleShot(0, &manager, SLOT(execute()));

     app.exec();
 }

 #include "main.moc"
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