[QNetworkAccessManager] Download a file -> "Unknown error" + crash of program

**AmirH** · 19th May 2015, 18:53

Hi,

I'm developping an app on windows which tooltips French news by the system tray.

After succesfully developped the functions that read xml files and fill them, I wanna download the rss file of lemonde.fr (which u know is a xml file) to add the last news in the local xml file.

I tried to do all necessary work for downloading that file but I have a "Unknown error" with reply->errorString(); and then the program crashes.

Here is the principal code :

Qt Code:

Switch view

Window::Window()
{
    AppVars::urlRSSlist << "http://rss.lemonde.fr/c/205/f/3050/index.rss";
    AppVars::netManList<< new QNetworkAccessManager(this);
    QObject::connect (AppVars::netManList[0], SIGNAL(finished(QNetworkReply*)), this, SLOT(downloadedRSSalaune(QNetworkReply*))) ;
    for(int i=0;i<AppVars::urlRSSlist.size();i++){
        qDebug() << "enter for loop for i = "+QString::number(i);
        AppVars::netManList[i]->get(QNetworkRequest(QUrl(AppVars::urlRSSlist[i])));
    }
 
}
 
void Window::downloadedRSSalaune(QNetworkReply* reply){
 
    qDebug() << reply->errorString();
 
    QByteArray data =QByteArray(reply->readAll());
 
    QList<QString> titleList;
    QList<QString> linkList;
    QDomDocument *domfile = new QDomDocument("alaune_xml");
    if(!(domfile->setContent(data))){
        return;
    }
 
    QDomNode principalNode = domfile->documentElement();
    QDomNode channelNode = principalNode.namedItem("rss").namedItem("channel");
    QDomNodeList listItems = channelNode.childNodes();
 
    int k = 0;
    int i = 0;
    while(k<10 && i<listItems.length()){
        if(listItems.at(i).nodeName() == "item"){
            qDebug() << listItems.at(i).namedItem("title").toElement().text();
            titleList << listItems.at(i).namedItem("title").toElement().text();
            linkList << listItems.at(i).namedItem("link").toElement().text();
            ++k;
        }
        ++i;
    }
 
    firstInsert10ArticlesXML(titleList, linkList, "alaune");
 
    tooltipInstantNews("DirectNews France","Les articles sont maintenant Ã  jours.","");
}
 
 
void Window::firstInsert10ArticlesXML(QList<QString> titles, QList<QString> links, QString cat)
{
    QString filepath = QCoreApplication::applicationDirPath();
    filepath.append("\\history.xml");
    AppFiles::historyXML->setFileName(filepath);
 
    if(!(AppFiles::historyXML->open(QIODevice::ReadOnly))){
        return;
    }
 
    // QDomDocument to parse xml file
    QDomDocument *domfile = new QDomDocument("history_xml");
    if(!(domfile->setContent(AppFiles::historyXML))){
        return;
    }
    AppFiles::historyXML->close();
 
    QList<QDomElement *> newItems;
    for(int i = 0; i<10; i++){
        newItems<<new QDomElement(domfile->createElement("item"));
 
        QDomElement titleSubItem = domfile->createElement("title");
        QDomText titleText = domfile->createTextNode(titles[i]);
        QDomElement linkSubItem = domfile->createElement("link");
        QDomText linkText = domfile->createTextNode(links[i]);
 
        titleSubItem.appendChild(titleText);
        linkSubItem.appendChild(linkText);
        newItems[i]->appendChild(titleSubItem);
        newItems[i]->appendChild(linkSubItem);
    }
 
    QDomNode principalNode = domfile->documentElement();
 
    QDomNode catNode = principalNode.namedItem(cat);
 
    if(catNode.isNull())
        return;
 
    for(int i = 0; i<10; i++){
        catNode.insertBefore(*newItems[i],catNode.firstChild());
    }
 
    QString write_doc = domfile->toString();
 
    if(!(AppFiles::historyXML->open(QIODevice::WriteOnly))){
        return;
    }
 
    AppFiles::historyXML->resize(0);
    QTextStream stream(AppFiles::historyXML);
    stream << write_doc;
    AppFiles::historyXML->close();
 
    ReadXML();
}
 
void Window::ReadXML()
{
    QString filepath = QCoreApplication::applicationDirPath();
    filepath.append("\\history.xml");
    AppFiles::historyXML->setFileName(filepath);
 
    if(!(AppFiles::historyXML->open(QIODevice::ReadOnly))){
        return;
    }
 
    // QDomDocument to parse xml file
    QDomDocument *domfile = new QDomDocument("history_xml");
    if(!(domfile->setContent(AppFiles::historyXML))){
        return;
    }
    AppFiles::historyXML->close();
 
    QDomNode principalNode = domfile->documentElement();
 
    QList<QDomNode> listNodes;
    listNodes<<principalNode.namedItem("alaune")<<principalNode.namedItem("monde")<<principalNode.namedItem("politique")<<principalNode.namedItem("societesante")
               <<principalNode.namedItem("economie")<<principalNode.namedItem("science")<<principalNode.namedItem("art")<<principalNode.namedItem("sport")
                 <<principalNode.namedItem("people");
 
    for(int k=0;k<9;k++){
        QDomNode item = listNodes[k].firstChild();
        int i = 0;
        while(!listNodes[k].isNull() && !item.isNull() && i<10){
            //for each article found, enable the QAction, and attribute text and link
            listArticles[k][i]->setEnabled(true);
            QString titleTrunc = item.namedItem("title").toElement().text();
            if(titleTrunc.size() > 50)
                titleTrunc = titleTrunc.left(50).append("...");
            listArticles[k][i]->setText(titleTrunc);
            AppVars::listShortcuts[k][i] = item.namedItem("link").toElement().text();
            ++i;
            item = item.nextSibling();
        }
    }
}
 
void Window::tooltipInstantNews(QString title, QString categorie, QString url)
{
    // recieved from getrssthread.cpp, show directly (no use of any xml file) the news and attribute system tray message link
    sticon->setToolTip(categorie+" : \n"+title);
    AppVars::shortcutMessage = url;
    if(AppVars::NotifBool)
        sticon->showMessage(categorie,title,QSystemTrayIcon::Information);
 
}

Window::Window()
{
    AppVars::urlRSSlist << "http://rss.lemonde.fr/c/205/f/3050/index.rss";
    AppVars::netManList<< new QNetworkAccessManager(this);
    QObject::connect (AppVars::netManList[0], SIGNAL(finished(QNetworkReply*)), this, SLOT(downloadedRSSalaune(QNetworkReply*))) ;
    for(int i=0;i<AppVars::urlRSSlist.size();i++){
        qDebug() << "enter for loop for i = "+QString::number(i);
        AppVars::netManList[i]->get(QNetworkRequest(QUrl(AppVars::urlRSSlist[i])));
    }

}

void Window::downloadedRSSalaune(QNetworkReply* reply){

    qDebug() << reply->errorString();

    QByteArray data =QByteArray(reply->readAll());

    QList<QString> titleList;
    QList<QString> linkList;
    QDomDocument *domfile = new QDomDocument("alaune_xml");
    if(!(domfile->setContent(data))){
        return;
    }

    QDomNode principalNode = domfile->documentElement();
    QDomNode channelNode = principalNode.namedItem("rss").namedItem("channel");
    QDomNodeList listItems = channelNode.childNodes();

    int k = 0;
    int i = 0;
    while(k<10 && i<listItems.length()){
        if(listItems.at(i).nodeName() == "item"){
            qDebug() << listItems.at(i).namedItem("title").toElement().text();
            titleList << listItems.at(i).namedItem("title").toElement().text();
            linkList << listItems.at(i).namedItem("link").toElement().text();
            ++k;
        }
        ++i;
    }

    firstInsert10ArticlesXML(titleList, linkList, "alaune");

    tooltipInstantNews("DirectNews France","Les articles sont maintenant Ã  jours.","");
}


void Window::firstInsert10ArticlesXML(QList<QString> titles, QList<QString> links, QString cat)
{
    QString filepath = QCoreApplication::applicationDirPath();
    filepath.append("\\history.xml");
    AppFiles::historyXML->setFileName(filepath);

    if(!(AppFiles::historyXML->open(QIODevice::ReadOnly))){
        return;
    }

    // QDomDocument to parse xml file
    QDomDocument *domfile = new QDomDocument("history_xml");
    if(!(domfile->setContent(AppFiles::historyXML))){
        return;
    }
    AppFiles::historyXML->close();

    QList<QDomElement *> newItems;
    for(int i = 0; i<10; i++){
        newItems<<new QDomElement(domfile->createElement("item"));

        QDomElement titleSubItem = domfile->createElement("title");
        QDomText titleText = domfile->createTextNode(titles[i]);
        QDomElement linkSubItem = domfile->createElement("link");
        QDomText linkText = domfile->createTextNode(links[i]);

        titleSubItem.appendChild(titleText);
        linkSubItem.appendChild(linkText);
        newItems[i]->appendChild(titleSubItem);
        newItems[i]->appendChild(linkSubItem);
    }

    QDomNode principalNode = domfile->documentElement();

    QDomNode catNode = principalNode.namedItem(cat);

    if(catNode.isNull())
        return;

    for(int i = 0; i<10; i++){
        catNode.insertBefore(*newItems[i],catNode.firstChild());
    }

    QString write_doc = domfile->toString();

    if(!(AppFiles::historyXML->open(QIODevice::WriteOnly))){
        return;
    }

    AppFiles::historyXML->resize(0);
    QTextStream stream(AppFiles::historyXML);
    stream << write_doc;
    AppFiles::historyXML->close();

    ReadXML();
}

void Window::ReadXML()
{
    QString filepath = QCoreApplication::applicationDirPath();
    filepath.append("\\history.xml");
    AppFiles::historyXML->setFileName(filepath);

    if(!(AppFiles::historyXML->open(QIODevice::ReadOnly))){
        return;
    }

    // QDomDocument to parse xml file
    QDomDocument *domfile = new QDomDocument("history_xml");
    if(!(domfile->setContent(AppFiles::historyXML))){
        return;
    }
    AppFiles::historyXML->close();

    QDomNode principalNode = domfile->documentElement();

    QList<QDomNode> listNodes;
    listNodes<<principalNode.namedItem("alaune")<<principalNode.namedItem("monde")<<principalNode.namedItem("politique")<<principalNode.namedItem("societesante")
               <<principalNode.namedItem("economie")<<principalNode.namedItem("science")<<principalNode.namedItem("art")<<principalNode.namedItem("sport")
                 <<principalNode.namedItem("people");

    for(int k=0;k<9;k++){
        QDomNode item = listNodes[k].firstChild();
        int i = 0;
        while(!listNodes[k].isNull() && !item.isNull() && i<10){
            //for each article found, enable the QAction, and attribute text and link
            listArticles[k][i]->setEnabled(true);
            QString titleTrunc = item.namedItem("title").toElement().text();
            if(titleTrunc.size() > 50)
                titleTrunc = titleTrunc.left(50).append("...");
            listArticles[k][i]->setText(titleTrunc);
            AppVars::listShortcuts[k][i] = item.namedItem("link").toElement().text();
            ++i;
            item = item.nextSibling();
        }
    }
}

void Window::tooltipInstantNews(QString title, QString categorie, QString url)
{
    // recieved from getrssthread.cpp, show directly (no use of any xml file) the news and attribute system tray message link
    sticon->setToolTip(categorie+" : \n"+title);
    AppVars::shortcutMessage = url;
    if(AppVars::NotifBool)
        sticon->showMessage(categorie,title,QSystemTrayIcon::Information);

}

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I may have to put some if(!ERROR) but I don't know where and how.

Window class derivates from QWidget
AppVars::urlRSSlist is a QList<String> (global var)
AppVars::netManList is a QList<QNetworkAccessManager*> (global var)

if something not clear, please tell me.

Thank u in advance for your help.

**wysota** · 19th May 2015, 19:51

Show us the debugger stack trace.

**AmirH** · 19th May 2015, 21:14

I really don't remember how to debug.

So I just activated debug mode, put a "red point" just before reply->errorString(); and run as debug.

A lot of things I don't understood appeared and I have a message:
Signal received from Operating system
name SIGSEGV
Meaning: segmentation fault

in a tab below, i have this:
0x66c01df4 8b 30 mov (%eax),%esi

Added after 11 minutes:

how should I check error of reply before QByteArray data =QByteArray(reply->readAll());

I should make a if(reply is null or error or anything else)

Added after 14 minutes:

ok I put :

Qt Code:

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if(reply->error() != QNetworkReply::NoError)
        return;

if(reply->error() != QNetworkReply::NoError)
        return;

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and it don't seems to return, but I still have "Unkown error" , i don't know why

I will arrange my code so no more segmentation error.

I'll come back if another ptoblem arrive,

still don't understand the "Unknown error"

**wysota** · 19th May 2015, 21:15

Originally Posted by AmirH

I really don't remember how to debug.

Well... I'm sure the web is full of information on how to do that so you can refresh your knowledge.

**AmirH** · 19th May 2015, 21:28

it was just a segmentation fault because of bad use of QList,

but the problem is that i still have qDebug() << reply->errorString(); which return "Unknown error", I have if(reply->error() != QNetworkReply::NoError) which not return (good

) and then i put:

qDebug() <<reply->readAll(); which print an empty string ( i see that by "" printed in application output)

but : http://rss.lemonde.fr/c/205/f/3050/index.rss has some result ... so I don't know where to look

**AmirH** · 20th May 2015, 11:53

Qt Code:

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int statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
    qDebug() << QVariant(statusCode).toString();

int statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
    qDebug() << QVariant(statusCode).toString();

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prints 200

reply->readAll(); is always empty

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