TCP Server

[rennreh]

Hello,
I want to Create a simple TCP-Server.

#include <QObject>
#include <QTcpSocket>
#include <QTcpServer>
#include <QAbstractSocket>
#include <QDebug>


class TCP_Server : public QObject {
   Q_OBJECT
public:
   TCP_Server(QObject *parent = 0);

signals:

public slots:
   void newConnection();
   void startRead();


private:
   QTcpServer *server;
   QTcpSocket *client;
};

/*
*
* */
TCP_Server::TCP_Server(QObject*parent):
   QObject(parent) {

   server = new QTcpServer(this);

   connect(server,SIGNAL(newConnection()),
           this,SLOT(newConnection()));

   if(!server->listen(QHostAddress::Any, 9999)) {
       qDebug() << "Server could not start";
   }else{
       qDebug() << "Server started!";
   }
}
/*
*
* */
void TCP_Server::newConnection() {
   client = server->nextPendingConnection();

   client->write("hello client\r\n");
   client->flush();

   client->waitForBytesWritten(3000);

   //socket->close();
}
/*
*
* */
void TCP_Server::startRead() {
   // get the information
   QByteArray Data = client->readAll();

   // will write on server side window
   qDebug() <<  " Data in: " << Data;

   client->write(Data);
}

and main:

#include <QCoreApplication>
#include <tcp_server.h>

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);

    TCP_Server server;

    return a.exec();
}

Why it Crash my program at line 3 in funktion void TCP_Server::newConnection()?
I see it has a real adress??

[OwonaVivienD]

Hi, rennreh,

Before playing with the QTcpClient returned by QTcpServer::nextPendingConnection, you should perform some verifications:

• is the pointer client not null?
• if it isn't, is the returned QTcpClient valid and connected?
• etc.

[rennreh]

Hello,
Client is not NULL and the connection is ok.

I have the program improved and asked about null but I get a segmentation fault.

void TCP_Server::newConnection() {
    client = server->nextPendingConnection();

    if(NULL==client) {
        qDebug() <<  "Addr is NULL: " << endl;
    }else{
        client->write("hello client\r\n");
        client->flush();

        client->waitForBytesWritten(3000);

        //socket->close();
    }
}

If I make following code it works:

void TCP_Server::newConnection() {
    QTcpSocket *socket = server->nextPendingConnection();

    if(NULL==socket ) {
        qDebug() <<  "Addr is NULL: " << endl;
    }else{
        socket ->write("hello client\r\n");
        socket ->flush();

        socket ->waitForBytesWritten(3000);

        //socket ->close();
    }
}

[asanka424]

What is the error you get, segfault?
Is it client->flush() gives the crash?

[rennreh]

If i Debug the programm I see it crash at line client->write with message:

"The inferiror stopped because it received a signal from the operating system. Signal name: SIGSEGV / Signal meaning: Segementation fault"