Using Visual Leak Detector

问题

I have C++ code that crashes randomly. In the code I have used some of the Qt libraries. The compiler is MSVS 2010. Based on some suggestions that this could be due to memory leaks, I started looking in this using Visual Leak Detector. I am very new to Visual Leak Detector and memory leak detection.

Here is the code in main.cpp:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
   return a.exec();
}

And also the MainWindow constructor looks like this:

MainWindow::MainWindow(QWidget *parent) :
        QMainWindow(parent)
    ,   m_Inputdevice(QAudioDeviceInfo::defaultInputDevice())
    ,   m_audioInput(0)
    ,   m_input(0)
    ,   m_iVolume(0)
    ,   m_buffer(BufferSize, 0)
    ,   ui(new Ui::MainWindow)
{  // LINE 23
    ui->setupUi(this);
    initializeAudio(); // LINE 26
    udpSocket = new QUdpSocket(this); 
    udpSocket1 = new QUdpSocket(this);
    ...
    char* str = new char [30]; 
    VLDEnable();
    VLDReportLeaks(); 
}

And the destructor is:

MainWindow::~MainWindow()
{
  delete udpSocket;
  delete udpSocket1;
  delete m_audioInput;
  delete ui;
}

Based on some suggestions I just installed it and got the following results:

WARNING: Visual Leak Detector detected memory leaks!
---------- Block 1 at 0x00CDED68: 12 bytes ----------
Call Stack:
c:\tmp\mainwindow.cpp (23): TestProgram.exe!MainWindow::MainWindow + 0x59 bytes
c:\tmp\main.cpp (7): TestProgram.exe!main + 0xA bytes
c:\myqt\4.8.2\src\winmain\qtmain_win.cpp (131): TestProgram.exe!WinMain + 0x12 bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (547): TestProgram.exe!__tmainCRTStartup + 0x2C bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (371): TestProgram.exe!WinMainCRTStartup
0x756233AA (File and line number not available): kernel32.dll!BaseThreadInitThunk + 0x12 bytes
0x77139EF2 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x63 bytes
0x77139EC5 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x36 bytes
Data:
C8 F9 CD 00    38 FD CD 00    28 3B 6E 02                    ....8... (;n.....



---------- Block 2 at 0x00CDF9C8: 20 bytes ----------
Call Stack:
c:\tmp\generatedfiles\ui_mainwindow.h (36): TestProgram.exe!Ui_MainWindow::setupUi + 0x7 bytes
c:\tmp\mainwindow.cpp (26): TestProgram.exe!MainWindow::MainWindow
c:\tmp\main.cpp (7): TestProgram.exe!main + 0xA bytes
c:\myqt\4.8.2\src\winmain\qtmain_win.cpp (131): TestProgram.exe!WinMain + 0x12 bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (547): TestProgram.exe!__tmainCRTStartup + 0x2C bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (371): TestProgram.exe!WinMainCRTStartup
0x756233AA (File and line number not available): kernel32.dll!BaseThreadInitThunk + 0x12 bytes
0x77139EF2 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x63 bytes
0x77139EC5 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x36 bytes
Data:
5C 90 DA 00    18 FA CD 00    38 90 DA 00    00 00 CD CD     \....... 8.......
CC FA CD 00                                                  ........ ........


---------- Block 3 at 0x00CDFD38: 20 bytes ----------
Call Stack:
c:\tmp\generatedfiles\ui_mainwindow.h (38): TestProgram.exe!Ui_MainWindow::setupUi + 0x7 bytes
c:\tmp\mainwindow.cpp (26): TestProgram.exe!MainWindow::MainWindow
c:\tmp\main.cpp (7): TestProgram.exe!main + 0xA bytes
c:\myqt\4.8.2\src\winmain\qtmain_win.cpp (131): TestProgram.exe!WinMain + 0x12 bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (547): TestProgram.exe!__tmainCRTStartup + 0x2C bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (371): TestProgram.exe!WinMainCRTStartup
0x756233AA (File and line number not available): kernel32.dll!BaseThreadInitThunk + 0x12 bytes
0x77139EF2 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x63 bytes
0x77139EC5 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x36 bytes
Data:
24 8F DA 00    88 FD CD 00    00 8F DA 00    00 00 CD CD     $....... ........
3C FE CD 00                                                  <....... ........


---------- Block 4 at 0x026E3B28: 20 bytes ----------
Call Stack:
c:\tmp\generatedfiles\ui_mainwindow.h (41): TestProgram.exe!Ui_MainWindow::setupUi + 0x7 bytes
c:\tmp\mainwindow.cpp (26): TestProgram.exe!MainWindow::MainWindow
c:\tmp\main.cpp (7): TestProgram.exe!main + 0xA bytes
c:\myqt\4.8.2\src\winmain\qtmain_win.cpp (131): TestProgram.exe!WinMain + 0x12 bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (547): TestProgram.exe!__tmainCRTStartup + 0x2C bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (371): TestProgram.exe!WinMainCRTStartup
0x756233AA (File and line number not available): kernel32.dll!BaseThreadInitThunk + 0x12 bytes
0x77139EF2 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x63 bytes
0x77139EC5 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x36 bytes
Data:
24 8F DA 00    78 3B 6E 02    00 8F DA 00    00 00 CD CD     $...x;n. ........
2C 3C 6E 02                                                  ,<n..... ........


---------- Block 6 at 0x026E4200: 8 bytes ----------
Call Stack:
c:\tmp\mainwindow.cpp (28): TestProgram.exe!MainWindow::MainWindow + 0x7 bytes
c:\tmp\main.cpp (7): TestProgram.exe!main + 0xA bytes
c:\myqt\4.8.2\src\winmain\qtmain_win.cpp (131): TestProgram.exe!WinMain + 0x12 bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (547): TestProgram.exe!__tmainCRTStartup + 0x2C bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (371): TestProgram.exe!WinMainCRTStartup
0x756233AA (File and line number not available): kernel32.dll!BaseThreadInitThunk + 0x12 bytes
0x77139EF2 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x63 bytes
0x77139EC5 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x36 bytes
Data:
34 8D DA 00    50 49 6E 02                                   4...PIn. ........


---------- Block 5 at 0x026E4C90: 12 bytes ----------
Call Stack:
c:\tmp\mainwindow.cpp (76): TestProgram.exe!MainWindow::createAudioInput + 0x7 bytes
c:\tmp\mainwindow.cpp (67): TestProgram.exe!MainWindow::initializeAudio
c:\tmp\mainwindow.cpp (28): TestProgram.exe!MainWindow::MainWindow
c:\tmp\main.cpp (7): TestProgram.exe!main + 0xA bytes
c:\myqt\4.8.2\src\winmain\qtmain_win.cpp (131): TestProgram.exe!WinMain + 0x12 bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (547): TestProgram.exe!__tmainCRTStartup + 0x2C bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (371): TestProgram.exe!WinMainCRTStartup
0x756233AA (File and line number not available): kernel32.dll!BaseThreadInitThunk + 0x12 bytes
0x77139EF2 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x63 bytes
0x77139EC5 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x36 bytes
Data:
74 91 DA 00    A0 4B 6E 02    78 50 6E 02                    t....Kn. xPn.....


---------- Block 7 at 0x026E54C8: 8 bytes ----------
Call Stack:
c:\tmp\mainwindow.cpp (29): TestProgram.exe!MainWindow::MainWindow + 0x7 bytes
c:\tmp\main.cpp (7): TestProgram.exe!main + 0xA bytes
c:\myqt\4.8.2\src\winmain\qtmain_win.cpp (131): TestProgram.exe!WinMain + 0x12 bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (547): TestProgram.exe!__tmainCRTStartup + 0x2C bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (371): TestProgram.exe!WinMainCRTStartup
0x756233AA (File and line number not available): kernel32.dll!BaseThreadInitThunk + 0x12 bytes
0x77139EF2 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x63 bytes
0x77139EC5 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x36 bytes
Data:
34 8D DA 00    10 55 6E 02                                   4....Un. ........


---------- Block 8 at 0x026E62D8: 30 bytes ----------
Call Stack:
c:\tmp\mainwindow.cpp (33): TestProgram.exe!MainWindow::MainWindow + 0x7 bytes
c:\tmp\main.cpp (7): TestProgram.exe!main + 0xA bytes
c:\myqt\4.8.2\src\winmain\qtmain_win.cpp (131): TestProgram.exe!WinMain + 0x12 bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (547): TestProgram.exe!__tmainCRTStartup + 0x2C bytes
f:\dd\vctools\crt_bld\self_x86\crt\src\crtexe.c (371): TestProgram.exe!WinMainCRTStartup
0x756233AA (File and line number not available): kernel32.dll!BaseThreadInitThunk + 0x12 bytes
0x77139EF2 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x63 bytes
0x77139EC5 (File and line number not available): ntdll.dll!RtlInitializeExceptionChain + 0x36 bytes
Data:
CD CD CD CD    CD CD CD CD    CD CD CD CD    CD CD CD CD     ........ ........
CD CD CD CD    CD CD CD CD    CD CD CD CD    CD CD           ........ ........

I appreciate any help to find out where the memory leak/s come from based on these results.

回答1:

Check your code of main.cpp file -- there are some errors.

There is a rule -- to every new must have its delete.

In your constructor, strange variable char* str = new char [30]; is declared, allocated, but never freed.

And what is m_buffer(BufferSize, 0) and m_Inputdevice(QAudioDeviceInfo::defaultInputDevice())?

回答2:

Don't explicitly delete your Qt objects if you have set a parent.

QObjects organize themselves in object trees. Giving Qt widgets and the like a parent, transfers ownership of the widget to that parent. Upon destruction the parent will take care of cleaning its children up. In those instances, your new does not need a matching delete. In fact, if you do so it will cause you problems.

At the very least you don't require