how to write integer to QTableWidget

Leopold

Hello,
have a new problem.I get some numbers from a QTableWidget.Then I do some mathematics with these and want to write the result to a second QTableWidget.
Programm does the mathematic but when its up to writing to the second Widget I get a segmentation fault```
double mbar1=0;
double druck1=0;
QString drehz,druck;

void MainWindow::on_sparkadv_clicked()
{
int r=m_ui->logfilewidget->rowCount();
for(int i = 1; i <12; ++i)
{ m_ui->average->insertRow(i);}
for (int i = 1; i <r; ++i)
{

    drehz = m_ui->logfilewidget->item(i,1)->text();
    druck = m_ui->logfilewidget->item(i,6)->text();

            if (drehz<1000)
                 {
                 druck1 =druck1 + druck.toDouble();}
                 }

int durchschnitt1=druck1/r;
m_ui->average->item(5,5)->setText(QString::number(durchschnitt1).toStdString().c_str());

}

inline void QTableWidgetItem::setText(const QString &atext)
{ setData(Qt::DisplayRole, atext); }

Thank you for your help!
Leopold

Leopold

sorry some text is missing:
here it stops in the qtablewidget.h

inline void QTableWidgetItem::setText(const QString &atext)
{ setData(Qt::DisplayRole, atext); }

aha_1980

Hi @Leopold,

start the program in a debugger. When it crashes, inpect the stack trace to find the root of the crash.

Regards

SGaist

Hi,

If there's a segmentation fault then you are accessing something that does not exists. You can use the debugger to find out what is going on.

I would guess that you are accessing a non existing item.

mrjj

Hi
do note that ->item(row,col) can return a NULL if no item is assigned and that is
instant crash.

You do
for(int i = 1; i <12; ++i)
m_ui->average->insertRow(i);}

But i don't see you assign any QTableWidgetItem and as far as i know insertRow
inserts empty row so
m_ui->average->item(5,5) might return NULL;

aha_1980

@Leopold said in how to write integer to QTableWidget:

@mrjj is fully right with the nullptr. By the way:

m_ui->average->item(5,5)->setText(QString::number(durchschnitt1).toStdString().c_str());

can be more simply written as:

m_ui->average->item(5,5)->setText(QString::number(durchschnitt1));

Leopold

Hi mrjj,
I had extra inserted this loop, because i thaught .possibly it will not recognice the rows.No help after deleting that row.

@ SGaist and aha_1980

yes debuging should resolve that problem.But Iam not used to debugging.I know already that inserting stops in line 188 from qtablewidget.h , thats why I attached the code where it stops. I do not know if "setData(Qt::DisplayRole, atext); " corresponds with
"setText(QString::number(durchschnitt1).toStdString().c_str()"
Debugger says "Wert" of atext = "0"

Leopold

@aha_1980

that was one of my first tries, always segmentation fault.

aha_1980

@Leopold

But Iam not used to debugging.

Then learn it. Take the 15 minutes for this video, for example: https://www.youtube.com/watch?v=B7UsWtyhXh4

that was one of my first tries, always segmentation fault.

If you use the debugger, it will probably tell you that you access a nullptr.

AS @mrjj said:

But i don't see you assign any QTableWidgetItem and as far as i know insertRow
inserts empty row so
m_ui->average->item(5,5) might return NULL;

You need to insert a QTableWidgetItem first.

Regards

SGaist

Additional note: QTableWidget::insertRow explicitly state: Inserts an empty row into the table at row. The crucial word here is: empty. There's no item there.

Leopold

@Leopold

i could figure out that my mathematics does not work, i am trying to solve that problem and will report again!

Leopold

Thank you for the help, now its working, i have added a counter for the division and changed the write comand.

double mbar1=0;
double druck1=0;
QString drehz,druck;
double durchschnitt1;
int durchschnitt;
double s=0;
void MainWindow::on_sparkadv_clicked()
{
    int r=m_ui->logfilewidget->rowCount();

         for (int i = 1; i <r; ++i)
                 {
                 drehz = m_ui->logfilewidget->item(i,1)->text();
                 druck = m_ui->logfilewidget->item(i,6)->text();

                if (drehz<1000)
                     {
                     druck1 = druck1 + druck.toDouble();
                     s=s+1;
                     }
                    }
                double durchschnitt1 = druck1 / s;
                int durchschnitt=durchschnitt1;
          
           m_ui->average->setItem(5,5,new QTableWidgetItem(QString::number(durchschnitt)));
      }