QT app:exec is blocking the code.

Christian Ehrlicher

@Ayush-Gupta said in QT app:exec is blocking the code.:

hence I cannot use QTcpSocket.

Why not? It's simple tcp ...

Ayush Gupta

Hi,

I am trying this on QT GUI app.

Created one UDP socket class and initializes the port. Now I am trying to write the data using WriteDatagram function. Function returns value as successful (the number of bytes written)

but when I am trying to read the data gram in my other application from same port using normal sockets I am not able read anything.

On other hand if cach readyRead() signal I am able to read the data in same QT-GUI application.

JonB

@Ayush-Gupta
Don't know, it's your other application's read code that is at issue. As we have said, Qt socket stuff is just standard, the fact that it comes from Qt or uses synchronous/asynchronous calls is not relevant. There is no "normal" vs "Qt" sockets.

Purely at a guess, since you originally said your other app was doing TCP, now it;s not doing UDP, or it;s listening on the wrong port. Use WireShark or similar if you want to check what's being sent around.

Ayush Gupta

Now I corrected the mistake the address given in sin_addr was wrong. I mentioned it now as
127.0.0.1

with this I am able to receive message from UdpSocket from QT application to normal socket in non-qt application but when I am trying to send message from my non-qt application to QT application signal readyRead not emitted and not able to read the data.

JonB

@Ayush-Gupta
Then you are doing something wrong in your receiving side, or possibly at the sender side. What else do you want us to say? Simple sample code is given in https://doc.qt.io/qt-5/qudpsocket.html. You have bound to the port for receiving, haven't you?

Ayush Gupta

@JonB I am pasting my code here

UdpSocket.h

#ifndef UDPSOCKET_H
#define UDPSOCKET_H
#include <QUdpSocket>
#include <MMISimForm.h>

class UdpSocket : public QObject
{

    Q_OBJECT
public:
       UdpSocket(QObject* parent, int portno, MMISimForm* simForm_);
       ~UdpSocket();

private:
       int portNo_;
       MMISimForm* mmiSimForm_;
       QUdpSocket *socketUdp;

public slots:
       void dataRead();

//methods
public:
       int sendData();

};

#endif // UDPSOCKET_H

UdpSocket.cpp

#include "UdpSocket.h"


UdpSocket::UdpSocket(QObject *parent, int portno, MMISimForm* simForm_)
          :QObject(parent), portNo_(portno), mmiSimForm_(simForm_)
{

    socketUdp = new QUdpSocket(this);
    socketUdp->bind(QHostAddress::LocalHost, portNo_);
    connect(socketUdp, SIGNAL(readyRead()), this, SLOT(dataRead()));
}


UdpSocket::~UdpSocket()
{

}

void UdpSocket::dataRead()
{
    QByteArray buffer;
    QHostAddress sender;
    quint16 senderPort;
    buffer.resize(socketUdp->pendingDatagramSize());
    int test = socketUdp->readDatagram(buffer.data(), buffer.size(),
                                        &sender, &senderPort);
    QString text;
    text.sprintf("Bytes Read %d", test);
    mmiSimForm_->logMessage(buffer);
}

int UdpSocket::sendData()
{
     return socketUdp->writeDatagram("GetStream", QHostAddress::LocalHost,
                               5000);
}

My non - qt application code

ServerSocket.cpp

#include "ServerSocket.h"
#include "mmisimlogger.h"
ServerSocket::ServerSocket()
{
    WSAStartup(0x0101, &w) != 0;
    /* Open a datagram socket */
    sd = socket(AF_INET, SOCK_DGRAM, 0);

    /* Clear out server struct */
    memset((void *)&server, '\0', sizeof(struct sockaddr_in));
    memset((void *)&client, '\0', sizeof(struct sockaddr_in));
    server.sin_family = AF_INET;
    server.sin_port = htons(5000);

    /* Get host name of this computer */
    gethostname(host_name, sizeof(host_name));
    hp = gethostbyname(host_name);

     /*Assign the address
    server.sin_addr.S_un.S_un_b.s_b1 = hp->h_addr_list[0][0];
    server.sin_addr.S_un.S_un_b.s_b2 = hp->h_addr_list[0][1];
    server.sin_addr.S_un.S_un_b.s_b3 = hp->h_addr_list[0][2];
    server.sin_addr.S_un.S_un_b.s_b4 = hp->h_addr_list[0][3];*/
    server.sin_addr.S_un.S_addr = inet_addr("127.0.0.1");

    bind(sd, (struct sockaddr *)&server, sizeof(struct sockaddr_in));

}

int ServerSocket::recieveData()
{

    client_length = (int)sizeof(struct sockaddr_in);
    int test = 0;



    //Receive bytes from client
    bytes_received = recvfrom(sd, buffer, 4096, 0, (struct sockaddr *)&client, &client_length);




     bytes_received = sendto(sd, (const char *)"hello", strlen("hello"),
                            0, (const struct sockaddr *) &client,
                               client_length);




    char teststring[40];
    sprintf(teststring,"ErrorCode %d", bytes_received);
    MMISimLogger::instance()->log(teststring);
    MMISimLogger::instance()->close();


    if (bytes_received < 0)
    {

    }
    else
    {
        test = bytes_received;
        //MMISimLogger::instance()->log(buffer);
        //MMISimLogger::instance()->close();
        return test;
    }
}

I know this code is mess but I don't know where I am doing wrong.

[Fixed code tags ~kshegunov]

Ayush Gupta

It seems that readyRead signal will be not be emitted when we send data from other non-QT application.

I am able to connect to the server (QT application side) when I send data using send() in non-QT application it returns number of byte send correctly but no readyRead signal is emitted.

J.Hilk

@Ayush-Gupta said in QT app:exec is blocking the code.:

It seems that readyRead signal will be not be emitted when we send data from other non-QT application.

No, there is no differentiation between Qt and non Qt UDP-Source. I'm able to receive and send UDP datagrams just fine that way.

I am able to connect to the server (QT application side) when I send data using send() in non-QT application it returns number of byte send correctly but no readyRead signal is emitted.

Pls make sure you actually really send data. A 3rd Party listening software could help here.

JonB

@Ayush-Gupta said in QT app:exec is blocking the code.:

It seems that readyRead signal will be not be emitted when we send data from other non-QT application.

As said multiple times, there is no difference in socket operation between a Qt program versus a non-Qt one, nor between blocking or non-blocking. TCP is TCP, UDP is UDP, regardless of who the sender/receiver is.

Concentrate instead on discovering what you are doing differently/wrong in either side of the communication.

Ayush Gupta

@J-Hilk Is it possible for you to share the example code?

Ayush Gupta

void MyTcpServer::incomingConnection(qintptr socketDescriptor)
{
    socket = new QTcpSocket();

    ```
// set the ID
    if(!socket->setSocketDescriptor(socketDescriptor))
    {
        //OnErrorSocket(socket->error());
        return;
    }
    else
    {
        simForm_->logMessage("Server Started");
        socket->setSocketOption(QAbstractSocket::KeepAliveOption, 1);
        //OnConnected();
    }

    // connect socket and signal
    // note - Qt::DirectConnection is used because it's multithreaded
    //        This makes the slot to be invoked immediately, when the signal is emitted.
    connect(socket, SIGNAL(readyRead()), this, SLOT(OnReadyRead()), Qt::DirectConnection);
    connect(socket, SIGNAL(disconnected()), this, SLOT(OnDisconnected()));
}


incomingConnection call is success means  connection is successful.
But when sending data using below function. ready Read is not emitting.

int ServerSocket::sendData()
{
   send(sd , "hello" , strlen("hello") , 0 );
}

ClientSocket::ClientSocket()
{
    WSAStartup(0x0101, &w) != 0;
    /* Open a datagram socket */
    sd = socket(AF_INET, SOCK_STREAM, 0);

    /* Clear out server struct */
    memset((void *)&server, '\0', sizeof(struct sockaddr_in));

    server.sin_family = AF_INET;
    server.sin_port = htons(5000);
    server.sin_addr.S_un.S_addr = inet_addr("127.0.0.1");

    connect(sd, (struct sockaddr *)&server, sizeof(server));
}

Ayush Gupta

@J-Hilk @JonB Is I am doing anything wrong in code?

J.Hilk

@Ayush-Gupta said in QT app:exec is blocking the code.:

@J-Hilk Is it possible for you to share the example code?

maybe I would have to cut out as significant part, to be able to show it

2nd post

Here you're using a TcpSocket, previously you posted Udp. What is it, do you use both at the same time?

@J-Hilk @JonB Is I am doing anything wrong in code?

are you sure you pass the correct port when creating the class. I noticed, your write function has hardcoded port value while your bind uses a value defined at run time

Ayush Gupta

@J-Hilk Yes I am using same port number. I failed using UDP then I am trying using UDP.

Port number is used correctly that is why connection was established and incomingConnection() was called.

Ayush Gupta

@J-Hilk Is it possible for you to post some working code?