QT TCP Socket | Send more than one command

[GCE_]

Hi guys!
I am on Windows using QT Creator4.12.4 + QT 5.15
For a small Home Project I have a power supply module, where I can send commands over TCP to enable voltage, set current, get serial number and so on
I wanted to write a small test application(console based) to set the voltage etc..
My problem is to send one command, wait for response from the module(i get the same sent command back) and after that i want to send another command.
I am a beginner in QT and now googling for 2 days and couldn find a soultion, I hope you guys can help me out. This is my code now:

#include <QCoreApplication>
#include <QtNetwork>
#include <QAbstractSocket>
#include <iostream>
#include <tcpsever.h>
#include <sockettest.h>
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    sockettest mTest;
    mTest.ConnectSocket();
    while (mTest.isConnected) {
        mTest.writeToPsu();
    }
    return a.exec();
}

Header for tcp client:

#ifndef SOCKETTEST_H
#define SOCKETTEST_H

#include <QObject>
#include <QTcpSocket>
#include <QAbstractSocket>

class sockettest : public QObject
{
    Q_OBJECT
public:
    explicit sockettest(QObject *parent = nullptr);
    void ConnectSocket();
    void writeToPsu();
    bool isConnected;

signals:
public slots:
    void connected();
    void disconnected();
    void bytesWritten(qint64 bytes);
    void readyRead();

private:
    QTcpSocket *socket;

};

#endif // SOCKETTEST_H

Implementation File for connection+disconnect+method for writing to PSU

#include "sockettest.h"
#include <iostream>

sockettest::sockettest(QObject *parent) : QObject(parent)
{

}

void sockettest::ConnectSocket()
{
    socket = new QTcpSocket(this);
    connect(socket, SIGNAL(connected()), this, SLOT(connected()));
    connect(socket, SIGNAL(disconnected()), this, SLOT(disconnected()));
    connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()));
    connect(socket, SIGNAL(bytesWritten(qint64)), this, SLOT(bytesWritten(qint64)));
    qDebug()<<"Connecting...";
    socket->connectToHost("192.168.0.198",44440);
    //socket->waitForConnected(1000);
    if(!socket->waitForConnected(5000)){
        isConnected=false;
        qDebug()<<"Error: "<<socket->errorString();
    }
}

void sockettest::writeToPsu()
{
    qDebug()<<"Is connected: "<<isConnected;
    QTextStream qtin(stdin);
    QString command;
    qDebug()<<"Enter command:";
    qtin>>command;
    socket->write(command.toUtf8());
    socket->waitForBytesWritten();
}

void sockettest::connected()
{
    qDebug() << "Connected!";
    isConnected=true;
    //writeToPsu();
    /*QTextStream qtin(stdin);
    QString command;
    qDebug()<<"Enter command:";
    qtin>>command;
    socket->write(command.toUtf8());*/
    //Commands for PSU
    //Voltage: OUT[x]:VOLTAGE:XXXX -> xxxx in mV
    //Current: OUT[x]:CURRENT:XXXX -> in mA
    //socket->write("OUT1:CURRENT:500");
    //Get Identification of PSU
    //socket->write("*IDN?");
    //Get Serial Number of PSU
    //socket->write("*SERIAL?");
    //Get SW Version of PSU
    //socket->write("*SW?");
}

void sockettest::disconnected()
{
    qDebug() << "Disconnected!";
    isConnected=false;
}

void sockettest::bytesWritten(qint64 bytes)
{
    qDebug() << "We wrote: " << bytes;
}

void sockettest::readyRead()
{
    QByteArray array;
    qDebug() << "Reading...";
    while (socket->bytesAvailable()) {
        array+=socket->readAll();
    }
    qDebug() << array;
    qDebug()<<"Reading finished!";
}

Sorry for such a big post like this, I hope you can help me out! :)
Thanks in advance!

[J.Hilk]

hi @GCE_ and welcome

remove this while loop

while (mTest.isConnected) {
mTest.writeToPsu();
}

it's blocking the event loop.
Even worse in your case, as it blocks a.exec(); from being called -> no event loop at all.

The rest is ok for a first draft, but for production code, do not mix signal slots ( connect(aaa..., bbbb, cccc,dddd)) and waitForXXX calls

Stick with one, preferably with signal and slots.

---

Gave you an upvote so you can answer more frequently than once per 5 minutes :D

[GCE_]

@J-Hilk
Thank you!
I removed the while loop now
I have the function writeToPsu()
Where in your opinion should I use this function?
And what exactly do you mean that I shouldn't mix signals and slots?

[J.Hilk]

@GCE_

And what exactly do you mean that I shouldn't mix signals and slots?

I said you shouldn't mix signal/slots with waitForSomecondition() calls, that is mixing synchronous with asynchronous apis

You can probably place it here

void sockettest::connected()
{
    qDebug() << "Connected!";
    isConnected=true;
   writeToPsu();
}

right after you get notified that your connection was successful

[GCE_]

Okay I did that and I get this now:

After Reading finished (OUT1:VOLTAGE:0 is Response from the PSU Module) I want again to send a command to the module

This is for now my biggest problem how to implement it.
So I want to enter as many commands as I want until I close the terminal

[J.Hilk]

@GCE_
well, for start, you can simply add

writeToPsu();

after

qDebug()<<"Reading finished!";

That will continuously send your single command.

If you want to change what you send, I would suggest creating a list of commands to send, and simply increment the index each readyRead call.

That way you will send all commands one after the other until you reach the end of your list

[GCE_]

Thank you!
I now call the writeToPsu() method after reading finished and now it works the way I want!
Thank you very much for this!
Still have so many things to learn in QT but I am liking it more and more :D
Thank you!