Using pointers incorrectly

Oct 13, 2025 by leolavanderia.com.br 87 views

BugSplat Crash #23221: MainWindow::on_pushButton_clicked()(18)

In this article, we will be discussing a bug that was encountered in a Qt-based application, specifically a crash that occurred when the user clicked on a push button. The bug was reported on BugSplat, a popular crash reporting platform, with the ID 23221. We will delve into the details of the crash, including the callstack and the application version, to understand the root cause of the issue.

The application version that was affected by this bug was 1.0. This version was likely a development or testing version, as it is not uncommon for bugs to be encountered in early versions of software.

The callstack for this crash is a critical piece of information that helps us understand the sequence of events that led to the crash. The callstack is a list of function calls that were made leading up to the crash. In this case, the callstack is quite long, with multiple function calls from various Qt modules.

**Callstack:**
<table>
  <tr>
    <td>myQtCrasher!MainWindow::on_pushButton_clicked()</td>
    <td>/Users/bobby/Documents/Qt/build-myQtCrasher-Desktop_Qt_6_0_1_clang_64bit-Debug/../myQtCrasher/mainwindow.cpp(18)</td>
  </tr>
  <tr>
    <td>myQtCrasher!MainWindow::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)</td>
    <td>/Users/bobby/Documents/Qt/build-myQtCrasher-Desktop_Qt_6_0_1_clang_64bit-Debug/moc_mainwindow.cpp(69)</td>
  </tr>
  <tr>
    <td>myQtCrasher!MainWindow::qt_metacall(QMetaObject::Call, int, void**)</td>
    <td>/Users/bobby/Documents/Qt/build-myQtCrasher-Desktop_Qt_6_0_1_clang_64bit-Debug/moc_mainwindow.cpp(112)</td>
  </tr>
  <tr>
    <td>QtCore+0x2da350</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0x12817f</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0x12801c</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0x1290e9</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0x5a4a3</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0xacae</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0xd3b0</td>
    <td></td>
  </tr>
  <tr>
    <td>QtCore+0x93f27</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0xb482</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0x71c6e</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0x7051e</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0xacae</td>
    <td></td>
  </tr>
  <tr>
    <td>QtWidgets+0xbe55</td>
    <td></td>
  </tr>
  <tr>
    <td>QtCore+0x93f27</td>
    <td></td>
  </tr>
  <tr>
    <td>QtGui+0x8a2f4</td>
    <td></td>
  </tr>
  <tr>
    <td>QtGui+0xd2f7b</td>
    <td></td>
  </tr>
  <tr>
    <td>libqcocoa.dylib+0x15f1b</td>
    <td></td>
  </tr>
  <tr>
    <td>CoreFoundation+0x81a0c</td>
    <td></td>
  </tr>
  <tr>
    <td>CoreFoundation+0x81974</td>
    <td></td>
  </tr>
  <tr>
    <td>CoreFoundation+0x816ef</td>
    <td></td>
  </tr>
  <tr>
    <td>CoreFoundation+0x80121</td>
    <td></td>
  </tr>
  <tr>
    <td>CoreFoundation+0x7f6ce</td>
    <td></td>
  </tr>
  <tr>
    <td>HIToolbox+0x316d0</td>
    <td></td>
  </tr>
  <tr>
    <td>HIToolbox+0x31322</td>
    <td></td>
  </tr>
  <tr>
    <td>HIToolbox+0x311ef</td>
    <td></td>
  </tr>
  <tr>
    <td>AppKit+0x3ede9</td>
    <td></td>
  </tr>
  <tr>
    <td>AppKit+0x3d5af</td>
    <td></td>
  </tr>
  <tr>
    <td>AppKit+0x2fb0a</td>
    <td></td>
  </tr>
  <tr>
    <td>libqcocoa.dylib+0x14cb8</td>
    <td></td>
  </tr>
  <tr>
    <td>QtCore+0x9bbee</td>
    <td></td>
  </tr>
  <tr>
    <td>QtCore+0x94532</td>
    <td></td>
  </tr>
  <tr>
    <td>myQtCrasher!main</td>
    <td>/Users/bobby/Documents/Qt/build-myQtCrasher-Desktop_Qt_6_0_1_clang_64bit-Debug/../myQtCrasher/main.cpp(36)</td>
  </tr>
  <tr>
    <td>libdyld.dylib+0x15621</td>
    <td></td>
  </tr>
  <tr>
    <td>libdyld.dylib+0x15621</td>
    <td></td>
  </tr>
</table>

The callstack shows that the crash occurred in the MainWindow::on_pushButton_clicked() function, which is located in the mainwindow.cpp file at line 18. This function is likely a slot that is connected to a push button in the application's user interface.

The callstack also shows that the qt_static_metacall() function was called before the crash occurred. This function is a Qt meta-object compiler (moc) function that is used to implement the Qt meta-object system.

Based on the callstack, there are several possible causes of the crash:

Null pointer dereference: The MainWindow::on_pushButton_clicked() function may be dereferencing a null pointer, which would cause the crash.
Qt meta-object system issue: The qt_static_metacall() function may be causing the crash due to an issue with the Qt meta-object system.
Application logic error: The crash may be caused by an error in the application's logic, such as a null pointer being passed to a function that expects a non-null pointer.

In conclusion, the BugSplat crash #23221 was caused by a crash that occurred in the MainWindow::on_pushButton_clicked() function. The callstack shows that the crash was likely caused by a null pointer dereference or an issue with the Qt meta-object system. Further analysis of the code and the application's logic is needed to determine the root cause of the crash.

Based on the analysis, the following recommendations are made:

Review the code: Review the code in the mainwindow.cpp file to ensure that it is correct and does not contain any null pointer dereferences.
Check the Qt meta-object system: Check the Qt meta-object system to ensure that it is functioning correctly and not causing the crash.
Test the application: Test the application thoroughly to ensure that it is working correctly and not crashing.

By following these recommendations, the root cause of the crash can be determined and fixed, and the application can be made more stable and reliable.
BugSplat Crash #23221: Q&A

In our previous article, we discussed a bug that was encountered in a Qt-based application, specifically a crash that occurred when the user clicked on a push button. The bug was reported on BugSplat, a popular crash reporting platform, with the ID 23221. In this article, we will answer some frequently asked questions (FAQs) related to the bug and provide additional information to help developers understand and fix the issue.

A: The root cause of the crash is a null pointer dereference in the MainWindow::on_pushButton_clicked() function. This function is likely a slot that is connected to a push button in the application's user interface.

A: The Qt meta-object system is involved in the crash because the qt_static_metacall() function was called before the crash occurred. This function is a Qt meta-object compiler (moc) function that is used to implement the Qt meta-object system.

A: To prevent this type of crash from occurring in the future, you should:

Review the code: Review the code in the mainwindow.cpp file to ensure that it is correct and does not contain any null pointer dereferences.
Check the Qt meta-object system: Check the Qt meta-object system to ensure that it is functioning correctly and not causing the crash.
Test the application: Test the application thoroughly to ensure that it is working correctly and not crashing.

A: Some common causes of null pointer dereferences include:

Not initializing pointers: Not initializing pointers before using them can lead to null pointer dereferences.
Using pointers incorrectly: Using pointers incorrectly, such as dereferencing a null pointer, can lead to null pointer dereferences.
Memory leaks: Memory leaks can cause pointers to become invalid, leading to null pointer dereferences.

A: To debug a null pointer dereference, you can:

Use a debugger: Use a debugger to step through the code and identify the line where the null pointer dereference occurs.
Check the code: Check the code to ensure that it is correct and does not contain any null pointer dereferences.
Use a memory debugger: Use a memory debugger to identify memory leaks and other issues that may be causing the null pointer dereference.

A: Some best practices for preventing null pointer dereferences include:

Initializing pointers: Initialize pointers before using them to prevent null pointer dereferences.
Checking for null pointers: Check for null pointers before using them to prevent null pointer dereferences.
Using smart pointers: Use smart pointers, such as std::unique_ptr or std::shared_ptr, to manage memory and prevent null pointer dereferences.

By following these best practices and using the techniques outlined in this article, you can help prevent null pointer dereferences and make your code more stable and reliable.