#include "test.h"
#include <QDataStream>
#include <QTimer>
#include <QtNetwork/QUdpSocket>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
socket = new QUdpSocket(this);
socket->bind(QHostAddress::LocalHost, receiverPort);
receiveDatagram();
}

void MainWindow::receiveDatagram()
{
if (socket->state() == QUdpSocket::BoundState)
{

    while (socket->hasPendingDatagrams())
    {
        QHostAddress senderAddress(QHostAddress::LocalHost);
        quint16 senderPort;
        datagram.resize(socket->pendingDatagramSize());
        socket->readDatagram(datagram.data(), datagram.size(), &senderAddress, &senderPort);
        //emit data_received(datagram);
        qDebug()<<datagram;
        sendDatagram();
    }
}

}

void MainWindow::sendDatagram()

{
QHostAddress receiverAddress(QHostAddress::LocalHost);

socket->writeDatagram(array, receiverAddress, receiverPort);
qDebug() << "Sent datagram to" << receiverAddress.toString() << ":" << receiverPort << "-" <<array;

}

examples in qt documentation explains separate separate modules.

I don't see what this should matter. You should test if it works. Merging the two functions into one class (for whatever abstruse reason) is a no brainer afterwards.

Why do you use port 55000 and QHostAddress::Any on the one side and receiver_port and receiver_host on the other?

Why do you check for a socket state in your slot? No example does this.

How does your debug output look like now?

#include "sender.h"
#include <QtNetwork/QUdpSocket>
#include <QMessageBox>
#include <exception>
#include <QTimer>
#include <QObject>


Sender::Sender()
    {
        send_socket = new QUdpSocket(this);
        socket = new QUdpSocket(this);
        qDebug()<<socket->bind(QHostAddress::Any,55000);
        connect(socket, &QUdpSocket::readyRead, this, &Sender::processResponse);
        QTimer* timer = new QTimer(this);
        connect(timer, &QTimer::timeout, this, &Sender::sendDatagram);
        timer->start(1000); // Adjust the interval as needed (milliseconds)


    }

    void Sender::sendDatagram()
    {
            qDebug()<<send_socket->writeDatagram(UDP_DATA, receiverAddress, receiverPort);
            qDebug() << "Sent datagram to" << receiverAddress.toString() << ":" << receiverPort << "-" <<UDP_DATA;
            //processResponse();
    }

    void Sender::processResponse()
    {   if (socket->state() == QUdpSocket::BoundState)
            {
                while (socket->hasPendingDatagrams()) {

                    datagram.resize(socket->pendingDatagramSize());
                    QHostAddress senderAddress;
                    quint16 senderPort;
                    int bytesRead = socket->readDatagram(datagram.data(), datagram.size(), &senderAddress, &senderPort);
                    QString data = QString::fromUtf8(datagram);

                    qDebug() << "Received datagram from" << senderAddress.toString() << ":" << senderPort << "-" << data;
                    if (bytesRead == -1)
                    {
                        qDebug() << "Failed to read datagram!";
                    }
                    else
                    {
                        QString data = QString::fromUtf8(datagram);
                        qDebug() << "Received datagram from" << senderAddress.toString() << ":" << senderPort << "-" << data;

                    }
                }
            }
    }

returns -1 which indicates it is not receiving bytes. I think the reson why it is not calling the receving function might be due to

This does not match since your code correctly calls readDatagram() when the receive function was called due to readyRead.
Post yor actual code and a proper error description.

/edit: also try out the examples and make sure the windows firewall does not block the udp packets

where can i found the error?

on my case,the number of bytes returned every time are 30:

30
Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"
30
Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"
30

#include "sender.h"
#include <QtNetwork/QUdpSocket>
#include <QMessageBox>
#include <exception>
#include <QTimer>
#include <QObject>


Sender::Sender()
    {
        send_socket = new QUdpSocket(this);
        socket = new QUdpSocket(this);
        send_socket->bind(QHostAddress("192.168.0.110"),500);
        socket->bind(QHostAddress("192.168.0.110"),4500);

        connect(socket, &QUdpSocket::readyRead, this, &Sender::processResponse);

        QTimer* timer = new QTimer(this);
        connect(timer, &QTimer::timeout, this, &Sender::sendDatagram);
        timer->start(1000); // Adjust the interval as needed (milliseconds)


    }

    void Sender::sendDatagram()
    {
            send_socket->writeDatagram(UDP_DATA, receiverAddress, receiverPort);
            qDebug() << "Sent datagram to" << receiverAddress.toString() << ":" << receiverPort << "-" <<UDP_DATA;
            
    }

    void Sender::processResponse()
    {
     
               if (socket->hasPendingDatagrams())
                {
                    datagram.resize(socket->pendingDatagramSize());
                    QHostAddress senderAddress;
                    quint16 senderPort;
                    socket->readDatagram(datagram.data(), datagram.size(), &senderAddress, &senderPort);
                    QString data = QString::fromUtf8(datagram);

                    qDebug() << "Received datagram from" << senderAddress.toString() << ":" << senderPort << "-" << data;
                }
                else
                {
                    qDebug() << "No pending datagrams.";
                }
    }

@JonB I have used two sockets- send_socket,socket

The socket (member?) variable you declare in Sender::Sender() and use in processResponse() is not bound/connected, it is simply a default empty socket. Why should it receive anything you send? Also you call send_socket->pendingDatagramSize() but socket->readDatagram().

If it still doesn't work, maybe try getting/connecting the second socket via connectToHost()?

Also,I couldn't understand the line :

Your sending code outputs that unconditionally after writeDatagram() without checking the result code,

how to check this,i didnt get it

Look at the documentation for writeDatagram(). The reason it returns a result is for people to check it.... Same for readDatagram().

Also,I couldn't understand the line :

Your sending code outputs that unconditionally after writeDatagram() without checking the result code,

how to check this,i didnt get it

obviously its correct:

How so? Your sending code outputs that unconditionally after writeDatagram() without checking the result code, so it tells us nothing about whether it was sent. In the time taken for you to ask about this and me to type a reply you could have made the change to test it. Up to you.

For sending/receiving to same host you might want to read e.g. https://stackoverflow.com/questions/18584679/testing-udp-on-localhost.

P.S.
I'm not an expert, but maybe you don't receive a datagram on the same socket as you send it on? Maybe you need to connect a second, separate socket to receive?

gives the output continously..obviously its correct:

Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"
Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"
Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"
Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"

Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"
Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"
Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"
Sent datagram to "192.168.0.110" : 4500 - "0,S,M,A,-1,-1,S,S,4000,10000,#"