i am a beginner in c++ and i am trying to retrieve data from a website using http request and to download the data in a file .

I am using the classes :

QMainWindow QtNetwork/QNetworkAccessManager QtNetwork/QNetworkRequest QtNetwork/QNetworkReply QUrl

The thing is that the file is created but there is no data in the file and i am getting an error that i don't understand . I searched through the forum found some similar kind of problems but did not understand as i am a beginner . Please help me its a school project and i am really stuck here.

Here is the httpWindow.h code


Qt Code: 
  1. #ifndef HTTPWINDOW_H
  2. #define HTTPWINDOW_H
  3.  
  4. #include <QMainWindow>
  5. #include <QtNetwork/QNetworkAccessManager>
  6. #include <QtNetwork/QNetworkRequest>
  7. #include <QtNetwork/QNetworkReply>
  8. #include <QUrl>
  9. #include <QString>
  10.  
  11. class QFile;
  12.  
  13. namespace Ui {
  14. class httpWindow;
  15. }
  16.  
  17. class httpWindow : public QMainWindow
  18. {
  19.     Q_OBJECT
  20.  
  21. public:
  22.     explicit httpWindow(QWidget *parent = 0);
  23.     ~httpWindow();
  24.     void request(QUrl url);
  25.  
  26. private slots:
  27.     void downloadFile();
  28.     void httpFinished();
  29.     void httpReadyRead();
  30. private:
  31.     Ui::httpWindow *ui;
  32.     QUrl url;
  33.     QNetworkAccessManager *manager;
  34.     QNetworkRequest requete;
  35.     QNetworkReply *reply;
  36.     QFile *file;
  37.     int httpGetId;
  38.     bool httpRequestAborted;
  39.  
  40. };
  41.  
  42. #endif // HTTPWINDOW_H
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Here is the httpwindow.cpp

Qt Code: 
  1. #include <QtWidgets>
  2. #include <qnetwork.h>
  3. #include <QString>
  4.  
  5. #include "httpwindow.h"
  6. #include "ui_httpwindow.h"
  7.  
  8. httpWindow::httpWindow(QWidget *parent) :
  9.     QMainWindow(parent),
  10.     ui(new Ui::httpWindow)
  11. {
  12.     ui->setupUi(this);
  13.     downloadFile();
  14. }
  15.  
  16. httpWindow::~httpWindow()
  17. {
  18.     delete ui;
  19. }
  20.  
  21. void httpWindow::request(QUrl url)
  22. {
  23.     manager =  new QNetworkAccessManager(this);
  24.     connect(manager, SIGNAL(finished()),
  25.             this, SLOT(httpFinished()));
  26.  
  27.     //requete.setUrl(QUrl("http://fxrates.fr.forexprostools.com/index.php?force_lang=5&pairs_ids=1;3;2;4;7;5;8;6;&header-text-color=%23FFFFFF&curr-name-color=%230059b0&inner-text-color=%23000000&green-text-color=%232A8215&green-background=%23B7F4C2&red-text-color=%23DC0001&red-background=%23FFE2E2&inner-border-color=%23CBCBCB&border-color=%23cbcbcb&bg1=%23F6F6F6&bg2=%23ffffff&bid=show&ask=show&last=show&change=hide&last_update=hide"));
  28.     requete.setUrl(url);
  29.  
  30.     reply = manager->get(requete);
  31.    connect(reply, SIGNAL(&reply::readyRead()), this, SLOT(httpReadyRead()));
  32. }
  33.  
  34. void httpWindow::downloadFile()
  35. {
  37.    QUrl url("http://fxrates.fr.forexprostools.com/index.php?force_lang=5&pairs_ids=1;3;2;4;7;5;8;6;&header-text-color=%23FFFFFF&curr-name-color=%230059b0&inner-text-color=%23000000&green-text-color=%232A8215&green-background=%23B7F4C2&red-text-color=%23DC0001&red-background=%23FFE2E2&inner-border-color=%23CBCBCB&border-color=%23cbcbcb&bg1=%23F6F6F6&bg2=%23ffffff&bid=show&ask=show&last=show&change=hide&last_update=hide") ;
  38.    qDebug() << url.toString();
  39.    QFileInfo fileInfo(url.path());
  40.     //msg.setText("fileInfo = " + fileInfo);
  41.     QString fileName = "C:\\testQt\\" + fileInfo.fileName();
  42.      msg.setText("fileName = " + fileName);
  43.  
  44.      if (fileName.isEmpty()){
  45.  
  46.         fileName = "C:\testQt\fichier.html";
  47.         msg.setText(" création d'un nouveau fichier fichier.html ");
  48.  
  49.     }
  50.     if (QFile::exists(fileName)) {
  51.         QFile::remove(fileName);
  52.         return;
  53.  
  54.  
  55.     }
  56.     file = new QFile(fileName);
  57.     msg.setText(" QFile::exists(fileName) == true , file : ");
  58.     if (!file->open(QIODevice::WriteOnly)) {
  59.  
  60.         delete file;
  61.         file = 0;
  62.         return;
  63.     }
  64.  
  65.  
  66.     // schedule the request
  67.     httpRequestAborted = false;
  68.     request(url);
  69.  
  70. }
  71.  
  72. void httpWindow::httpFinished()
  73. {
  74.     if (httpRequestAborted) {
  75.         if (file) {
  76.             file->close();
  77.             file->remove();
  78.             delete file;
  79.             file = 0;
  80.         }
  81.         reply->deleteLater();
  82.         return;
  83.     }
  84.  
  85.     file->flush();
  86.     file->close();
  87.  
  88.     QVariant redirectionTarget = reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
  89.     if (reply->error()) {
  90.         file->remove();
  91. //        QMessageBox::information(this, tr("HTTP"),
  92. //                                 tr("Download failed: %1.")
  93. //                                 .arg(reply->errorString()));
  94. //        downloadButton->setEnabled(true);
  95.     } else if (!redirectionTarget.isNull()) {
  96.         QUrl newUrl = url.resolved(redirectionTarget.toUrl());
  97. //        if (QMessageBox::question(this, tr("HTTP"),
  98. //                                  tr("Redirect to %1 ?").arg(newUrl.toString()),
  99. //                                  QMessageBox::Yes | QMessageBox::No) == QMessageBox::Yes) {
  100.             url = newUrl;
  101.             reply->deleteLater();
  102.             file->open(QIODevice::WriteOnly);
  103.             file->resize(0);
  104.             request(url);
  105.             return;
  106.  
  107.     }
  108.  
  109.     reply->deleteLater();
  110.     reply = 0;
  111.     delete file;
  112.     file = 0;
  113.  
  114. }
  115.  
  116.  
  117. void httpWindow::httpReadyRead()
  118. {
  119.     // this slot gets called every time the QNetworkReply has new data.
  120.     // We read all of its new data and write it into the file.
  121.     // That way we use less RAM than when reading it at the finished()
  122.     // signal of the QNetworkReply
  123.     if (file)
  124.         file->write(reply->readAll());
  125.  
  126. }
  127. Here is the main.cpp code
  128.  
  129. #include "httpwindow.h"
  130. #include <QApplication>
  131.  
  132. int main(int argc, char *argv[])
  133. {
  134.     QApplication a(argc, argv);
  135.     httpWindow w;
  136.     w.show();
  137.  
  138.     return a.exec();
  139. }
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The errors :

Qt Code: 
  1. can't find linker symbol for virtual table for `QMessageBox' value
  2.   found `RGB_MASK' instead
  3. can't find linker symbol for virtual table for `QMessageBox' value
  4.   found `RGB_MASK' instead
  5. "http://fxrates.fr.forexprostools.com/index.php?force_lang=5&pairs_ids=1;3;2;4;7;5;8;6;&header-text-color=%23FFFFFF&curr-name-color=%230059b0&inner-text-color=%23000000&green-text-color=%232A8215&green-background=%23B7F4C2&red-text-color=%23DC0001&red-background=%23FFE2E2&inner-border-color=%23CBCBCB&border-color=%23cbcbcb&bg1=%23F6F6F6&bg2=%23ffffff&bid=show&ask=show&last=show&change=hide&last_update=hide"
  6. QObject::connect: No such signal QNetworkAccessManager::finished() in ..\ppe3_trading_test\httpwindow.cpp:24
  7. QObject::connect:  (receiver name: 'httpWindow')
  8. QObject::connect: No such signal QNetworkReplyHttpImpl::&reply::readyRead() in ..\ppe3_trading_test\httpwindow.cpp:31
  9. QObject::connect:  (receiver name: 'httpWindow')
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Please do help me its really important for my schooling and its been 4 days i am trying to solve the problem .PLease help