title: Qt access violation 0xC0000005 after slot
body: <p>I have an issue that i just figured out what to do, so maybe you can help me.</p>
  
  <p>I am working on a application that connects to a database, displays the values and allowes the user to update/insert values.</p>
  
  <p>I have a <code>QTabView</code> and inside one of the tabs there are four <code>QTableWidget</code>'s.
  Inside this Tables is sometimes (depends on the value of the database) a <code>QComboBox</code> to select some predefined Values.
  I catch the <code>QComboBox::selectedIndexChanged(int)</code> with a <code>QSignalMapper</code> and have a <code>slot</code> connected to the <code>QSignalMapper</code> to give some information what table it was and what setting was changed. From time to time i create the SettingsMapper new (and delete it before that) to reset the 'outdated' mapper-combobox connections.</p>
  
  <p>So the problem is, that when i change the index inside a combobox, the slot gets called and i can debug into the moc_*.cpp where the switch of the signal/slot connections is, but after that i get the <code>access violation on address 0xC0000005</code> inside the dlls.</p>
  
  <p>Here the call stack:</p>
  
  <pre><code>QtCored4.dll!6721af70()     
  [Frames below may be incorrect and/or missing, no symbols loaded for QtCored4.dll]  
  QtCored4.dll!67219fe5()     
  QtCored4.dll!67218f14()     
  QtCored4.dll!67218e48()     
  QtCored4.dll!6721903d()     
  QtCored4.dll!6720f874()     
  QtCored4.dll!6702429b()     
  QtCored4.dll!670316f3()     
  QtGuid4.dll!655b93f1()  
  QtGuid4.dll!650f99d0()  
  user32.dll!7e41885a()   
  user32.dll!7e41882a()   
  user32.dll!7e42b326()   
  msctf.dll!7472467f()    
  user32.dll!7e43e1ad()   
  user32.dll!7e43e18a()   
  QtCored4.dll!67234b9c()     
  user32.dll!7e42b372()   
  user32.dll!7e418734()   
  user32.dll!7e418816()   
  user32.dll!7e4189cd()   
  user32.dll!7e418a10()   
  QtCored4.dll!672359b6()     
  ntdll.dll!7c90cfdc()    
  ntdll.dll!7c958e0d()    
  ntdll.dll!7c95932a()    
  ntdll.dll!7c90cfdc()    
  ntdll.dll!7c9594ca()    
  ntdll.dll!7c919ca7()    
  ntdll.dll!7c918f01()    
  ntdll.dll!7c91925d()    
  ntdll.dll!7c918f01()    
  ntdll.dll!7c9101bb()    
  ntdll.dll!7c9192ef()    
  ntdll.dll!7c918f01()    
  ntdll.dll!7c9101bb()    
  user32.dll!7e4277b0()   
  user32.dll!7e4277f7()   
  ntdll.dll!7c90da0c()    
  kernel32.dll!7c8024c7()     
  msctf.dll!74725951()    
  msctf.dll!74725956()    
  user32.dll!7e418a80()   
  user32.dll!7e418734()   
  user32.dll!7e418816()   
  ntdll.dll!7c96c6a7()    
  QtCored4.dll!6723c8f6()     
  datProgram.exe!__tmainCRTStartup()  Line 578 + 0x35 bytes   C
  datProgram.exe.exe!WinMainCRTStartup()  Line 403    C
  kernel32.dll!7c817067()     
  </code></pre>
  
  <p>`</p>
  
  <p>What makes me curios is, that in another tab is one <code>QTableWidget</code> with the same methods as described above, but the problem does not occur there.
  And when running in release version(Ctrl+F5) the problem also seems to be gone ... ò.Ó</p>
  
  <p>Any advice?</p>