Qt Creator Manual | Debugging a C++ Example Application

Qt Creator Manual 4.5.2

Debugging Qt Quick Projects ◦ Debugging a Qt Quick Example Application

# Debugging a C++ Example Application

This section uses the TextFinder example to illustrate how to debug Qt C++ applications in the Debug mode.

TextFinder reads a text file into QString and then displays it with QTextEdit. To look at the TextFinder class and see the stored data, place a breakpoint in textfinder.cpp, as follows:

1. Click in between the line number and the window border on the line where we change the cursor position to set a breakpoint.

2. Select Debug > Start Debugging > Start Debugging or press F5.
3. To view information about the breakpoint, go to the Breakpoints view.

4. To remove a breakpoint, right-click it and select Delete Breakpoint.
5. To view the base classes and data members of the TextFinder class, go to the Locals and Expressions view.

Modify the `on_findButton_clicked()` function to move back to the start of the document and continue searching once the cursor hits the end of the document. Add the following code snippet:

      void TextFinder::on_findButton_clicked()
      {
          QString searchString = ui->lineEdit->text();

          QTextDocument *document = ui->textEdit->document();
          QTextCursor cursor = ui->textEdit->textCursor();
          cursor = document->find(searchString, cursor,
              QTextDocument::FindWholeWords);
          ui->textEdit->setTextCursor(cursor);

          bool found = cursor.isNull();

          if (!found && previouslyFound) {
              int ret = QMessageBox::question(this, tr("End of Document"),
              tr("I have reached the end of the document. Would you like "
              "me to start searching from the beginning of the document?"),
              QMessageBox::Yes | QMessageBox::No, QMessageBox::Yes);

              if (ret == QMessageBox::Yes) {
                  cursor = document->find(searchString,
                      QTextDocument::FindWholeWords);
                  ui->textEdit->setTextCursor(cursor);
              } else
                  return;
          }
          previouslyFound = found;
      }

If you compile and run the above code, however, the application does not work correctly due to a logic error. To locate this logic error, step through the code using the following buttons: (Stop Debugger), (Step Over), (Step Into), and (Step Out).