[How to ?] Writing QTableWidget cells.

[john_god]

You have to alocate memory to your pointer

QTableWidgetItem *itab;
itab = new QTableWidgetItem; // add this line 
itab->setText("X");   
tableWidget->setItem(0, 0, itab);

QTableWidgetItem *itab;
itab = new QTableWidgetItem; // add this line 
itab->setText("X");   
tableWidget->setItem(0, 0, itab);

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It was crashing because you're setting a value to an unalolocate pointer.