Is data received from serial port possible to view on two forms?

[Shivam Sharma]

So, I have a program that receives data from serial port and displays it in the QtextEdit of the mainwindow form. I also want the same data strings on another second form but am not being able to figure out how. As in, the data on the mainwindow appears but when I open the second form to view it there is no data, it is blank.

Can anyone help me out?

[J.Hilk]

@Shivam-Sharma there are so many ways to do this.

How about you show us what you have, and what "doesn't" work and we go from there

[Shivam Sharma]

Ok. So, I have received the data from the serial port and it displays on the gui in a text box. For now attached a GPS sensor and hence i get the GPRMC string very well. Now i also want the same string to be displayed on my form2.

But writing the same code doesn't help. As in, in form 2 all I've changed is QSerialPort *serial1; that's it.

Here is the code:

QSerialPort *serial;
QString line;
QString txt1;
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
serial = new QSerialPort(this);
serial = new QSerialPort(this);
serial->setPortName("ttyUSB0");
serial->setBaudRate(QSerialPort::Baud9600);
serial->setDataBits(QSerialPort::Data8);
serial->setParity(QSerialPort::NoParity);
serial->setStopBits(QSerialPort::OneStop);
serial->setFlowControl(QSerialPort::NoFlowControl);

   if( serial->open(QIODevice::ReadWrite))
    {
        qDebug()<<"Port Open OK";
        connect(serial, &QSerialPort::readyRead, this, &MainWindow::serialReceived);
    }
  else
    {
        qDebug()<<"Can't Open Port : " << serial->error();
    }
   serialReceived();

}

void Setup::serialReceived()
{
QByteArray serialData;
serialData = serial1->readAll();

char t0[512];
static char t1[512];
static int wp=0;
unsigned int i=0;

QString filename="/home/user/Desktop/Programs/MainCBOT2/dataentry2.txt";
QFile file( filename );

if(file.open(QIODevice::WriteOnly | QIODevice::Append | QIODevice::Text))
{
    QTextStream stream( &file );
    strcpy(t0,serialData);
    for (i=0;i<strlen(t0);i++)
    {
        t1[wp++]=t0[i];
        wp%=512;
        t1[wp]=0;

        if(t0[i] == '\n')
        {
            wp=0;
            if(checksum_gps1(t1))
            {
                if(memcmp("$GPRMC",t1,6)==0)
                {
                    ui->receiver->append(t1);
                }
            }
        }
    }
    file.close();
}

}

[JonB]

@Shivam-Sharma
In your code the only mention of serial1 is in serialData = serial1->readAll();. So obviously that's an undeclared variable. C++ absolute basics. No idea what you expect.

[J.Hilk]

@Shivam-Sharma

ok, first of:

You can't open the same serial port twice. The OS will not allow it. SO simply copying the whole serial port implementation to get the same signal again is the worst way to do it ;)

I suggest the following:
inside MainWindo, define a signal

signals:
      void newSerialData(QString data);

and emit it where you also set it to your UI form

inside setup do this slot:

public slots:
     void onNewSerialData(QString data);
//.cpp
void Setup::onNewSerialData(QString data)
{
     ui->receiver->append(data);
}

than connect the signal to the slot (where you create the 2nd window)

connect(this, &MainWindow:: newSerialData, my2ndForm, &Setup:: onNewSerialData);

I would have been more specific on where to write what, but you only posted excerpts of your actual code 🤷‍♂️

[Shivam Sharma]

@J-Hilk Hey yeah, i guess excerpts are pretty vauge. I am getting what you want to convey but just not being able to do some silly issue. Pasting the entire code below,

//Mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <info.h>
#include <setup.h>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    Info *info;
    Setup *setup;

signals:
    void newSerialData(QString data);

private slots:
    void serialReceived();
    void on_infobutton_clicked();
    void on_setupbutton_clicked();

private:
    Ui::MainWindow *ui;

};
#endif // MAINWINDOW_H

//Mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <info.h>
#include <setup.h>

#include <QList>
#include <QComboBox>
#include <QString>
#include <QTextEdit>
#include <QTime>
#include <QDebug>
#include <QSerialPort>
#include <QtSerialPort/QSerialPortInfo>
#include <QFile>
#include <qmath.h>
#include <QList>

QSerialPort *serial;
QString line;
QString txt1;
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
       ui->setupUi(this);
       serial = new QSerialPort(this);
       serial = new QSerialPort(this);
       serial->setPortName("ttyUSB0");
       serial->setBaudRate(QSerialPort::Baud9600);
       serial->setDataBits(QSerialPort::Data8);
       serial->setParity(QSerialPort::NoParity);
       serial->setStopBits(QSerialPort::OneStop);
       serial->setFlowControl(QSerialPort::NoFlowControl);

       if( serial->open(QIODevice::ReadWrite))
        {
            qDebug()<<"Port Open OK";
            connect(serial, &QSerialPort::readyRead, this, &MainWindow::serialReceived);
        }
      else
        {
            qDebug()<<"Can't Open Port : " << serial->error();
        }
       serialReceived();
}

MainWindow::~MainWindow()
{
    delete ui;
    serial->close();
}

char *get_field(char *str,int fld)
{
    static char t0[512];
    int i=0,j=0,k=0;
    while(i<512)
    {
        if(*(str+i) == ',' || *(str+i) == '\n')
        {
            if (fld==j) return t0;
                j++;
                t0[0]=0;
                k=0;
        }
        else
        {
            t0[k++]=*(str+i);
            t0[k]=0;
        }
        i++;
    }
        t0[0]=0;
        return t0;
}

int checksum_gps(char *str)
{
    unsigned char cs=0,sum=0,i=0;
    char sCS[8], exit =0;

    while (i<250 && !exit)
    {
        if(*(str+i) == '*')
        {
            sum=0;
            break;
        }
        if(sum)
            cs^=*(str+i);
        if(*(str+i) == '$')
            sum=1;
        if(*(str+i) == 0)
            exit=1;
        i++;
    }
    sprintf(sCS,"%02X",cs);
    if (memcmp(sCS,str+i+1,2)==0)
        return 1;
    return 0;
}

char *timestamp(void)
{
    static char t0[128];
    long ms;
    time_t now;
    struct tm *t;
    struct timespec spec;

    time(&now);
    t= localtime(&now);
    clock_gettime(CLOCK_REALTIME, &spec);
    ms= round(spec.tv_nsec/1.0e6);

    sprintf(t0, "%04d/%02d/%02d %02d:%02d:%02d.%03ld ",
            t->tm_year+1900, t->tm_mon+1, t->tm_mday,
            t->tm_hour, t->tm_min, t->tm_sec, ms);
    return t0;
}

void MainWindow::serialReceived()
{
    QByteArray serialData;
    serialData = serial->readAll();
    QString static receivedData = QString::fromStdString(serialData.toStdString());

    char t0[512];
    static char t1[512];
    static int wp=0;
    unsigned int i=0;

    QString filename="/home/user/Desktop/Programs/MainCBOT2/entrydata.txt";
    QFile file( filename );

    if(file.open(QIODevice::WriteOnly | QIODevice::Append | QIODevice::Text))
    {
        QTextStream stream( &file );
        strcpy(t0,serialData);
        for (i=0;i<strlen(t0);i++)
        {
            t1[wp++]=t0[i];
            wp%=512;
            t1[wp]=0;

            if(t0[i] == '\n')
            {
                wp=0;
                if(checksum_gps(t1))
                {
                    if(memcmp("$GPRMC",t1,6)==0)
                    {
                        unsigned int latcnt1=0, log_cnt1=0,spdcnt=0, cogcnt=0;
                        char cog[20];
                        char spd[20];
                        char lat1[20], lg1[20];
                        for(i=20;i<28;i++)
                        {
                            lat1[latcnt1++]=t1[i];
                        }
                        float j=atof(lat1);
                        float k=(int)(j/100);
                        float minlat  = j - ( k * 100 );
                        float ddeglat = k + ( minlat / 60 );
                        ui->latitude->setText(QString::number(ddeglat,'f'));

                        for(i=33;i<42;i++)
                        {
                            lg1[log_cnt1++]=t1[i];
                        }
                        float p=atof(lg1);
                        float q=(int)(p/100);
                        float minlong  = p - ( q * 100 );
                        float ddeglong = q + ( minlong / 60 );
                        ui->longitude->setText(QString::number(ddeglong,'f'));

                        for (i=45;i<50;i++)
                        {
                            spd[spdcnt++]=t1[i];
                        }
                        float r=atof(spd);
                        ui->speed->setText(QString::number(r,'f',4));

                        for (i=50;i<56;i++)
                        {
                            cog[cogcnt++]=t1[i];
                        }
                        float u=atof((cog));
                        float w=u*0.514444;
                        ui->cog->setText(QString::number(w,'f',4));

                        stream<<strcat(t1,timestamp());
                        ui->rece->setText(t1);
                        fflush(stdout);
                    }
                }
            }
        }
        file.close();
    }
    ui->timest->setText(timestamp());
}

void MainWindow::on_infobutton_clicked()
{
    info = new Info(this);
    info->show();
}

void MainWindow::on_setupbutton_clicked()
{
    setup = new Setup(this);
    setup->show();
}

//Setup.h

#ifndef SETUP_H
#define SETUP_H
#include <mainwindow.h>
#include <QDialog>

namespace Ui {
class Setup;
}

class Setup : public QDialog
{
    Q_OBJECT

public:
    explicit Setup(QWidget *parent = nullptr);
    ~Setup();

public slots:
     void onNewSerialData(QString data);

private slots:
    void serialReceived1();
    void on_start_toggled(bool checked);

private:
    Ui::Setup *ui;
};

#endif // SETUP_H

//Setup.cpp

#include "setup.h"
#include "ui_setup.h"
#include <QSerialPort>
#include <QDebug>
#include <mainwindow.h>
#include <QSerialPortInfo>
#include <QFile>

//QSerialPort *serial1;
Setup::Setup(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Setup)
{
    ui->setupUi(this);
    ui->start->setCheckable(true);
    connect(this, &MainWindow:: newSerialData, Setup, &Setup:: onNewSerialData);
}

void Setup::onNewSerialData(QString data)
{
     ui->receiver->append(data);
}

---

Edit[j.hilk] added code tags for readability

[Shivam Sharma]

Here there is an error in connect, says: Setup doesn't refer to a value.

[JonB]

@Shivam-Sharma

connect(this, &MainWindow:: newSerialData, Setup, &Setup:: onNewSerialData);

Here there is an error in connect, says: Setup doesn't refer to a value.

As the message states. The Setup as the 3rd parameter is a class. You need an instance (just like you have for the 1st parameter). See the docs.

[J.Hilk]

@Shivam-Sharma
I said where you create Setup, you put the connect into the constructor of Setup

here:

void MainWindow::on_setupbutton_clicked()
{
    setup = new Setup(this);
    setup->show();
    connect(this, &MainWindow::newSerialData, setup, &Setup::onNewSerialData);
}

but, every time you click on the setupButton you will create a new instance of that class, you're leaking memory

---

Edit changed for error free connect, thanks to @JonB for mentioning it

[JonB]

@J-Hilk
As per my previous, to help the user in this case you should change your 3rd param from Setup to setup anyway. Unless you want him to figure for himself (which would not be a bad idea, bit late now that I have spoken!) :)

[Shivam Sharma]

@J-Hilk everthing is error free except one, which I ain't undertsanding:

'Setup' does not name a type.

[J.Hilk]

@Shivam-Sharma
where ?
It should point you to a line

---

actually, remove the mainwindow.h include from setup
here

#include "setup.h"
#include "ui_setup.h"
#include <QSerialPort>
#include <QDebug>
#include <mainwindow.h>
#include <QSerialPortInfo>
#include <QFile>

and here

#ifndef SETUP_H
#define SETUP_H
#include <mainwindow.h>
#include <QDialog>

thats a circular include with your mainwindow.h were you include setup.h

[JonB]

@Shivam-Sharma
As @J-Hilk has said. And further to that: (unless a Qt expert contradicts me) you should never be including mainwindow.h into anything other than mainwindow.cpp and your main.cpp, not into any other UI stuff you define. Keeps it clean --- they should never need to know about your MainWindow class. This is true all over the place: a widget which accesses/opens a "child" widget should include that child's .h file, but the "child" widgets should never need to know about/include the .h file of other ("parent") widgets where they might be called from. At least usually.

[Shivam Sharma]

This post is deleted!

[Shivam Sharma]

@J-Hilk @JonB

Thank you so much guys. This really helped me. All the solutions that you'll constantly engaged me with really means a lot. Appreciate this.

[SGaist]

Hi,

One small addition, when passing QString around like that (but it is also valid for other classes), it's a good habit to use const references. This allows to avoid creating unneeded copies.

[Shivam Sharma]

@J-Hilk @JonB Hi guys. Need one more help. If i want to add a push button on the Setup form that connects and disconnects the serial data incoming on both the forms how could I do that.

This is the code for the push button, i can do it on the mainwindow form but unable to do it on the Setup form since it is not being able to access *serial.

Code:

void MainWindow::on_start_toggled(bool checked)
{
    ui->start->setText(ui->start->isChecked() ? "Connect" : "Disconnect");
    if (checked)
    {
        serial->close();
        ui->start->setStyleSheet(QString("QPushButton {background-color: rgb(115, 210, 22);}"));
    }
    else
    {
        ui->start->setStyleSheet(QString("QPushButton {background-color: red;}"));


           serial = new QSerialPort(this);
           serial = new QSerialPort(this);
           serial->setPortName("ttyUSB0");
           serial->setBaudRate(QSerialPort::Baud9600);
           serial->setDataBits(QSerialPort::Data8);
           serial->setParity(QSerialPort::NoParity);
           serial->setStopBits(QSerialPort::OneStop);
           serial->setFlowControl(QSerialPort::NoFlowControl);

           if( serial->open(QIODevice::ReadWrite))
            {
                qDebug()<<"Port Open OK";
                connect(serial, &QSerialPort::readyRead, this, &MainWindow::serialReceived);
            }
          else
            {
                qDebug()<<"Can't Open Port : " << serial->error();
            }
           serialReceived();
    }
}

[jsulm]

@Shivam-Sharma Create a signal in Setup, connect that signal to clicked() signal of the button in Setup and then connect the signal you created in Setup (the first one I mentioned) to a slot in MainWindow where you can enable/disable the serial port.

[Shivam Sharma]

I am sorry, but unable to understand. How do i connect the pushbutton to mainwindow from Setup form, since i cannot inherit the parent class, neither can i create an instance of it. Could you give a demo?

[jsulm]

@Shivam-Sharma said in Is data received from serial port possible to view on two forms?:

How do i connect the pushbutton to mainwindow from Setup form

You don't, please read more carefully.

class Setup
{
signals:
    void onOffSerialPort();
};

void Setup::Setup()
{
    connect(ui->button, &QPushButton::clicked, this, &Setup::onOffSerialButton);
}

// MainWindow
connect(setup, &Setup::onOffSerialButton, this, &MainWindow::onOffSerialButton);

As you can see Setup does not know anything about MainWindow.