Qt - Downloading file from URL

[iQChange]

Hello.
I'm really new to Qt. I learnt GUI ~2 weeks. Now, I'm with networking.
Based on the Qt examples (almost a copy), I made this class:
(HEADER)

#ifndef QDOWNLOADER_HPP
#define QDOWNLOADER_HPP

#include <QObject>
#include <QByteArray>
#include <QString>
#include <QtNetwork>
#include <QDir>
#include <QFile>

class QDownloader : public QObject
{
    Q_OBJECT
    public:
    explicit QDownloader(QObject *parent = 0);
    QDownloader(const QString url, QObject* parent = 0, const QDir dir = QDir::currentPath());
    QString data() const;
    signals:
    void downloaded();
    public slots:
    void download(const QString url);
    private slots:
    void downloaded_file(QNetworkReply* reply);
    private:
    QNetworkAccessManager manager;
    QByteArray downloaded_data;
};

#endif // QDOWNLOADER_HPP 

(IMPLEMENTATIONS)

#include "qdownloader.hpp"
QDownloader::QDownloader(QObject *parent) :
    QObject(parent)
{

}

QDownloader::QDownloader(const QString url, QObject* parent, const QDir dir) :
    QObject(parent)
{
    this->download(url);
}

void QDownloader::download(const QString url)
{
    connect(&manager, SIGNAL(finished(QNetworkReply*)), SLOT(downloaded_file(QNetworkReply*)));
    QNetworkRequest request(url);
    manager.get(request);
}

void QDownloader::downloaded_file(QNetworkReply *reply)
{
    this->downloaded_data = reply->readAll();
    reply->deleteLater();
    emit downloaded();
}

QString QDownloader::data() const
{
    return QString(this->downloaded_data);
}

And using like that:

#include <QCoreApplication>
#include <QDebug>
#include "C:/cpp/libs/qdownloader.hpp"
int main(int argc, char* argv[])
{
    QCoreApplication app(argc, argv);
    QDownloader a("http://www.google.com/robots.txt");
    qDebug() << a.data();
    return app.exec();
}

But the program output is that:
http://s28.postimg.org/idb2jbtzh/error.png

What am I doing wrong? How to fix it?

[iQChange]

Anyone?

[norm b]

I think that those are just warnings. Notice that the last line is "".

The problem is that a network request is not made until the event loop executes (line 9 in main.cpp). So you get an empty QString at line 8 (the "").

Try adding a qDebug() as follows:

void QDownloader::downloaded_file(QNetworkReply *reply)
{
    this->downloaded_data = reply->readAll();
    qDebug() << downloaded_data;   // should get some output here
    reply->deleteLater();
    emit downloaded();
}