Memory leak...

[Ericode]

Hello, each time this button is pressed there seems to be a memory leak and I am not sure where it is coming from. Can anyone spot it?

void MainWindow::on_LoginPushButton_clicked()
{
    QString username, password;
    QSqlQuery qry;

    username = ui->lineEdit_Username->text();
    password = ui->lineEdit_Password->text();


    QUrl url = ("url entered here");
    QNetworkRequest request( url );
    request.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("application/x-www-form-urlencoded"));

    QJsonObject loginInfo;
    loginInfo["username"] = username;
    loginInfo["password"] = password;

    QJsonDocument doc(loginInfo);

    QByteArray bytes = doc.toJson();

    QNetworkAccessManager *nam = new QNetworkAccessManager();

    QNetworkReply *reply = nam->post(request,bytes);

    connect(reply, &QNetworkReply::finished, [=] {
        strReply = (QString)reply->readAll();
        QJsonDocument jsonDoc = QJsonDocument::fromJson(strReply.toUtf8());
        QJsonObject jsonObject = jsonDoc.object();

        if ( jsonObject["status"].operator ==("OK")) {
            ui->Username_Status->setText("<font color = 'green'>Successful Connection!</font>");
        }
        else {
            ui->Username_Status->setText("<font color = 'red'>Incorrect Username or Password</font>");
        }
        delete reply;
        delete nam;
    });
}

[mcosta]

Hi and welcome to devnet,

have you tried to use some tool to check memory usage (for instance http://valgrind.org/)??

[Ericode]

@mcosta
Hello, Yes I tried that and it was telling me delete nam; is the memory leak but I am confused about that.

[alex_malyu]

First check if connect actually connected anything.
bool c = connect.....

[onek24]

Hello @Ericode ,

thats what the QtDocs say about your problem(or the finished signal): Link

Note: Do not delete the object in the slot connected to this signal. Use deleteLater().

All you have to do is to replace the delete in your lambda expression with deleteLater():

nam.deleteLater();
reply.deleteLater();

So your full code will look like this:

void MainWindow::on_LoginPushButton_clicked()
{
    QString username, password;
    QSqlQuery qry;

    username = ui->lineEdit_Username->text();
    password = ui->lineEdit_Password->text();


    QUrl url = ("url entered here");
    QNetworkRequest request( url );
    request.setHeader(QNetworkRequest::ContentTypeHeader, QVariant("application/x-www-form-urlencoded"));

    QJsonObject loginInfo;
    loginInfo["username"] = username;
    loginInfo["password"] = password;

    QJsonDocument doc(loginInfo);

    QByteArray bytes = doc.toJson();

    QNetworkAccessManager *nam = new QNetworkAccessManager();

    QNetworkReply *reply = nam->post(request,bytes);

    connect(reply, &QNetworkReply::finished, [=] {
        strReply = (QString)reply->readAll();
        QJsonDocument jsonDoc = QJsonDocument::fromJson(strReply.toUtf8());
        QJsonObject jsonObject = jsonDoc.object();

        if ( jsonObject["status"].operator ==("OK")) {
            ui->Username_Status->setText("<font color = 'green'>Successful Connection!</font>");
        }
        else {
            ui->Username_Status->setText("<font color = 'red'>Incorrect Username or Password</font>");
        }
        reply.deleteLater();
        nam.deleteLater();
    });
}

For further informations about the deleteLater() read: QObject#deleteLater