How to detect memory leaks in MFC?

[ovidiucucu]

Q: Which is the simplest method for detecting memory leaks in MFC code?


A: Detecting memory leaks in MFC code is pretty simple because the MFC framework has bult-in support for that purpose.
Let’s take a short example:

#include "StdAfx.h"
#include "Foo.h"

CFoo::CFoo()
{
   m_buffer = new char[128];
   strcpy(m_buffer, "Baba Safta");
}

CFoo::~CFoo()
{
}

Also presume that delete operator is never called for freeing m_buffer.
After running then closing the program in debug mode, we can see in Debug window:

Detected memory leaks!
Dumping objects ->
{183} normal block at 0x0036B320, 128 bytes long.
 Data:  42 61 62 61 20 53 61 66 74 61 00 CD CD CD CD CD 
Object dump complete.
The program '[1758] MyTest.exe: Native' has exited with code 0 (0x0).

It shows that we have memory leaks and some additional info but it doesn't tell us the cause.
To find out the source code which generates memory leaks, we simply have to use DEBUG_NEW MFC macro.

#include "StdAfx.h"
#include "Foo.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

CFoo::CFoo()
{
   m_buffer = new char[128]; // <-- double click in "Debug" window to go here!
   strcpy(m_buffer, "Baba Safta");
}

CFoo::~CFoo()
{
   // <-- should free the buffer to avoid memory leaks!
}

Now, the Debug window looks a little bit different:

Detected memory leaks!
Dumping objects ->
c:\Projects\Test\Foo.cpp(10) : {183} normal block at 0x0036B320, 128 bytes long.
 Data:  42 61 62 61 20 53 61 66 74 61 00 CD CD CD CD CD 
Object dump complete.
The program '[3950] Test.exe: Native' has exited with code 0 (0x0).

Additional info were been added: the source file (c:\Projects\Test\Foo.cpp) and the line number which gnerates memory leaks (10). Moreover, if double-click in Debug window, the Visual Studio IDE jumps exactly in that source file at that line number.

Resources:

• MSDN: DEBUG_NEW

See also:

• Visual C++ Debugging: How to manage memory leaks?