QNetworkAccessManager example

MainWindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <stdint.h>
#include <vector>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_clicked()
{
    QNetworkAccessManager *mgr = new QNetworkAccessManager(this);
    QNetworkRequest req;
    req.setUrl(ui->lineEdit->text());
    req.setRawHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.154 Safari/537.36");

    resp = mgr->get(req);
    connect(resp, SIGNAL(readyRead()),                          this, SLOT(slotReadyRead()));
    connect(resp, SIGNAL(error(QNetworkReply::NetworkError)),   this, SLOT(slotError(QNetworkReply::NetworkError)));
    connect(resp, SIGNAL(sslErrors(QList<QSslError>)),          this, SLOT(slotSslErrors(QList<QSslError>)));
}

void MainWindow::slotReadyRead() {
    std::vector<char> buf;
    qint64 chunk;

    QString allbuf;

    while(resp->bytesAvailable() > 0) {
        chunk = resp->bytesAvailable();
        if(chunk > 4096)
            chunk = 4096;

        buf.resize(chunk + 1);
        memset(& buf[0], 0, chunk + 1);

        if(chunk != resp->read(& buf[0], chunk)) {
            ui->textBrowser->appendPlainText("-> read error");
        } else {
            ui->textBrowser->appendPlainText("-> read ok");
        }

        allbuf += & buf[0];
    }

    ui->textBrowser->setPlainText(allbuf);
}

void MainWindow::slotError(QNetworkReply::NetworkError) {

}

void MainWindow::slotSslErrors(QList<QSslError>) {

}

Where resp come from in 25 th line?

It was 5 years ago and I don't have the original code anymore, but it looks like resp is a field inside MainWindow class (so it should be in MainWindow.h), as well as it's type is QNetworkReply * (I think).