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Thread: Qt QNetworkAccessManager and Slot not working in C++

  1. 28th March 2015, 10:36 #1
    cruzo
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    Default Qt QNetworkAccessManager and Slot not working in C++

    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
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  2. 28th March 2015, 12:00 #2
    Lykurg
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    Default Re: Qt QNetworkAccessManager and Slot not working in C++

    Well, QNetworkAccessManager does have a signal called finished() ... but for the connection you also have to pass the signature
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  3. 28th March 2015, 12:54 #3
    cruzo
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    Default Re: Qt QNetworkAccessManager and Slot not working in C++

    Plz can you explain further what do you mean by signature ? and in the code i posted i have written this function :

    Qt Code: 
    1. void httpWindow::request(QUrl url)
    2. {
    3.     manager =  new QNetworkAccessManager(this);
    4.     connect(manager, SIGNAL(finished()),
    5.             this, SLOT(httpFinished()));
    6.  
    7.     //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"));
    8.     requete.setUrl(url);
    9.  
    10.     reply = manager->get(requete);
    11.    connect(reply, SIGNAL(&reply::readyRead()), this, SLOT(httpReadyRead()));
    12. }
    To copy to clipboard, switch view to plain text mode 


    Which is used in this download file function :

    Qt Code: 
    1. void httpWindow::downloadFile()
    2. {
    4.    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") ;
    5.    qDebug() << url.toString();
    6.    QFileInfo fileInfo(url.path());
    7.     //msg.setText("fileInfo = " + fileInfo);
    8.     QString fileName = "C:\\testQt\\" + fileInfo.fileName();
    9.      msg.setText("fileName = " + fileName);
    10.  
    11.      if (fileName.isEmpty()){
    12.  
    13.         fileName = "C:\testQt\fichier.html";
    14.         msg.setText(" création d'un nouveau fichier fichier.html ");
    15.  
    16.     }
    17.     if (QFile::exists(fileName)) {
    18.         QFile::remove(fileName);
    19.         return;
    20.  
    21.  
    22.     }
    23.     file = new QFile(fileName);
    24.     msg.setText(" QFile::exists(fileName) == true , file : ");
    25.     if (!file->open(QIODevice::WriteOnly)) {
    26.  
    27.         delete file;
    28.         file = 0;
    29.         return;
    30.     }
    31.  
    32.  
    33.     // schedule the request
    34.     httpRequestAborted = false;
    35.     request(url);
    36.  
    37. }
    To copy to clipboard, switch view to plain text mode 

    Do you think the code is right ? I mean do you see somthing that is missing ? I am really new at this please kindly help
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  4. 28th March 2015, 13:39 #4
    anda_skoa
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    Default Re: Qt QNetworkAccessManager and Slot not working in C++

    Quote Originally Posted by cruzo View Post
    Plz can you explain further what do you mean by signature ?
    The SIGNAL and SLOT macros need the name of the signal/slot and the types of their arguments.
    QNetworkAccessManager's finished() signal as an argument of type QNetworkReply*

    Quote Originally Posted by cruzo View Post
    Qt Code: 
    1. connect(reply, SIGNAL(&reply::readyRead()), this, SLOT(httpReadyRead()));
    To copy to clipboard, switch view to plain text mode 
    This connect is also wrong, the SIGNAL macro contains more than just the signal's signature.

    Cheers,
    _
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  5. 28th March 2015, 14:11 #5
    cruzo
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    Default Re: Qt QNetworkAccessManager and Slot not working in C++

    ok , so i changed some things in my code in the request () function :

    instead of this :
    Qt Code: 
    1. connect(reply, SIGNAL(&reply::readyRead()), this, SLOT(httpReadyRead()));
    To copy to clipboard, switch view to plain text mode 

    i changed into this :
    Qt Code: 
    1. connect(reply, SIGNAL(readyRead()), this, SLOT(httpReadyRead()));
    To copy to clipboard, switch view to plain text mode 

    and i added " QNetworkReply* " and it gives this :

    Qt Code: 
    1. connect(manager, SIGNAL(finished(QNetworkReply*)),
    2.             this, SLOT(httpFinished()));
    To copy to clipboard, switch view to plain text mode 

    So in the end i have this code for request ():

    Qt Code: 
    1. void httpWindow::request(QUrl url)
    2. {
    3.     manager =  new QNetworkAccessManager(this);
    4.     connect(manager, SIGNAL(finished(QNetworkReply*)),
    5.             this, SLOT(httpFinished()));
    6.  
    7.     //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"));
    8.     requete.setUrl(url);
    9.  
    10.     reply = manager->get(requete);
    11.    connect(reply, SIGNAL(readyRead()), this, SLOT(httpReadyRead()));
    12.    //connect(reply, SIGNAL(error(QNetworkReply::NetworkError)),
    13.               //SLOT(onError(QNetworkReply::NetworkError)));
    14. }
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    This is the code for httpFinished():

    Qt Code: 
    1. if (httpRequestAborted) {
    2.         if (file) {
    3.             file->close();
    4.             file->remove();
    5.             delete file;
    6.             file = 0;
    7.         }
    8.         reply->deleteLater();
    9.         return;
    10.     }
    11.  
    12.     file->flush();
    13.     file->close();
    14.  
    15.     QVariant redirectionTarget = reply->attribute(QNetworkRequest::RedirectionTargetAttribute);
    16.     if (reply->error()) {
    17.         file->remove();
    18.  
    19.     } else if (!redirectionTarget.isNull()) {
    20.         QUrl newUrl = url.resolved(redirectionTarget.toUrl());
    21.  
    22.             url = newUrl;
    23.             reply->deleteLater();
    24.             file->open(QIODevice::WriteOnly);
    25.             file->resize(0);
    26.             request(url);
    27.             return;
    28.  
    29.     }
    30.  
    31.     reply->deleteLater();
    32.     reply = 0;
    33.     delete file;
    34.     file = 0;
    35.  
    36. }
    To copy to clipboard, switch view to plain text mode 


    When i started Debug , i got these 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
    To copy to clipboard, switch view to plain text mode 

    and the application stucked saying it can not continue so i stopped the debug .

    Please help me identify these errors , i am sure you are more knowledge in these than me .
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