Valgrind not detecting memory leak after QObject connected

random_user

Hello, I'm new to using Valgrind and wanted to use it in a large project. Before that, I wrote a simple test to create a memory leak on purpose and see the output. But I failed to do so in a very specific case. When a QObject is created using new then connected via a signal/slot mechanism, Valgrind fails to detect it even if delete is not called !

7  int main(int argc, char *argv[])
8  {
9    QCoreApplication app(argc, argv);
10
11    Test* t = new Test();
12
13   /* Memory leak detected by Valgrind */
14    QTimer* timer_1 = new QTimer();
15
16    /* Memory leak NOT detected by Valgrind */
17    QTimer* timer_2 = new QTimer();
18    QObject::connect(timer_2, SIGNAL(timeout()), t, SLOT(timeoutSlot()));
19
20    /* Memory leak detected by Valgrind */
21    QTimer* timer_3 = new QTimer();
22    QObject::connect(timer_3, SIGNAL(timeout()), t, SLOT(timeoutSlot()));
23    QObject::disconnect(timer_3, SIGNAL(timeout()), t, SLOT(timeoutSlot()));
24
25    return 0;
26 }

Test is a simple QObject subclass with one slot doing nothing.
And here is what Valgrind output looks like:

144 (32 direct, 112 indirect) bytes in 1 blocks are definitely lost in loss record 33 of 39 | Location main.cpp:14
376 (32 direct, 344 indirect) bytes in 1 blocks are definitely lost in loss record 36 of 39 | Location main.cpp:21
504 (16 direct, 488 indirect) bytes in 1 blocks are definitely lost in loss record 37 of 39 | Location main.cpp:11

As you can see, memory leak on line 17 does not appear.

If possibly some memory leak escapes valgrind output, how can I make sure this does not happen in a larger project with many new, connect, etc ?

For the setup, I'm using QtCreator and the default Valgrind installation, no specific parameters were introduced.

Thank you

Christian Ehrlicher

int main(int argc, char *argv[])
{
  QCoreApplication app(argc, argv);

  /* Memory leak detected by Valgrind */
  QTimer* timer_1 = new QTimer();

  /* Memory leak NOT detected by Valgrind */
  QTimer* timer_2 = new QTimer();

  /* Memory leak detected by Valgrind */
  QTimer* timer_3 = new QTimer();

  return 0;
}

With this code valgrind properly shows 3 memleaks.