Delete QNetworkReply *reply cause SIGSEGV outside of the code? - c++

Question

I wrote a simple program to automate the process setting the router. After a check, I find a pointer need to be delete (QNetworkReply *reply in replyFinish())and do the job, but after that the program crash and Qt show it stopped in some assembly code :(
So my questions are:
Are there any common practices to handle situation like that (Qt
show the program stopped in some assembly code)
What did I do wrong when delete a pointer which isn't used anymore?
(pretty sure about that)
Here is the code:
#ifndef HTTPGETTER_H
#define HTTPGETTER_H
class QNetworkAccessManager;
class QNetworkReply;
class QNetworkRequest;
class QAuthenticator;
#include <QObject>
class httpGetter : public QObject
{
Q_OBJECT
private:
QNetworkAccessManager *nam;
public:
explicit httpGetter(QObject *parent=0);
~httpGetter();
public slots:
void replyFinish(QNetworkReply* reply);
void onAuthen(QNetworkReply*,QAuthenticator*);
};
implements
#include "httpgetter.h"
#include <QtNetwork/QNetworkRequest>
#include <QtNetwork/QNetworkReply>
#include <QtNetwork/QNetworkAccessManager>
#include <QAuthenticator>
#include <QDebug>
httpGetter::httpGetter(QObject *parent) : QObject(parent)
{
nam = new QNetworkAccessManager(this);
QObject::connect(nam,SIGNAL(finished(QNetworkReply*)),this,SLOT(replyFinish(QNetworkReply*)));
QObject::connect(nam,SIGNAL(authenticationRequired(QNetworkReply*,QAuthenticator*)),this,SLOT(onAuthen(QNetworkReply*,QAuthenticator*)));
QUrl url("http://192.168.1.1");
QNetworkReply *reply= nam->get(QNetworkRequest(url));
}
httpGetter::~httpGetter(){
delete nam;
}
void httpGetter::replyFinish(QNetworkReply *reply)
{
if (reply==NULL) {
qDebug() << "NULL reply";
return;
}
QVariant statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
qDebug() << statusCode.toString();
if (reply->error()==QNetworkReply::NoError) {
qDebug() << "NICE reply";
QByteArray bytes = reply->readAll();
QString answer = QString(bytes);
qDebug()<< answer;
}
else {
qDebug() << "reply error";
}
//delete reply; ==> delele cause sigsegv, if don't the program run like a while(true)
//reply == NULL;
}
void httpGetter::onAuthen(QNetworkReply* rep,QAuthenticator* auth)
{
if ( rep==NULL || auth == NULL) {
qDebug()<< "reply or authentication pointer is null";
return;
}
qDebug()<< rep->readAll();
auth->setUser("rolan");
auth->setPassword("123456");
}
main
#include <QtCore/QCoreApplication>
#include "httpgetter.h"
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
httpGetter abc;
return a.exec();
}

Answer 1

According to the documentation:
Note: After the request has finished, it is the responsibility of the
user to delete the QNetworkReply object at an appropriate time. Do not
directly delete it inside the slot connected to finished(). You can
use the deleteLater() function.
Also, since
nam = new QNetworkAccessManager(this);
creates a new QNetworkAccessManager with this as its parent, and QObject's destructor will automatically delete all of its children, your delete nam; in httpGetter's destructor is unnecessary and will end up causing a double delete.