FIX: MFC Reports Memory Leaks When cout and cin Are Used (130827)
The information in this article applies to:
- The Microsoft Foundation Classes (MFC), when used with:
- Microsoft Visual C++ for Windows, 16-bit edition 1.0
- Microsoft Visual C++ for Windows, 16-bit edition 1.5
- Microsoft Visual C++ for Windows, 16-bit edition 1.51
- Microsoft Visual C++ for Windows, 16-bit edition 1.52
- Microsoft Visual C++, 32-bit Editions 1.0
- Microsoft Visual C++, 32-bit Editions 2.0
- Microsoft Visual C++, 32-bit Editions 2.1
This article was previously published under Q130827 SYMPTOMS
An application that statically links to MFC and uses one of the C++ I/O
functions (cout, cin, cerr, or clog) generates memory leak messages when it
exits from the program. The messages look similar to this one:
Detected memory leaks!
Dumping objects ->
{3} non-object block at $002F05CC, 512 bytes long
{1} non-object block at $002F051C, 84 bytes long
Object dump complete.
The second line indicates a loss of 84 bytes for 32-bit editions and 28
bytes for 16-bit editions of Visual C++.
CAUSE
By referencing cout, cin, cerr, or clog you are causing these objects to do
a one-time allocation for their file-buffer objects. The file-buffer
objects are allocated using "operator new," and when you use MFC, these
allocations are mapped through MFC's debug allocator (an overridden version
of "operator new" that can be found in \MSVC\MFC\SRC\AFXMEM.CPP). There is
also a memory buffer 512 bytes long allocated by the Run-Time library.
Because these objects are allocated by the Run-Time Library, they are freed
by the Run-Time Library. However MFC's memory leak detection occurs before
the Run-Time Library has destroyed its global objects, so it appears to MFC
that there was an allocation made that has not been properly freed.
NOTE: This problem doesn't occur when the DLL version of the C/C++ Run-Time
Library is used (MSVCRT20.DLL) because the memory allocations come from
within the DLL and are not mapped through MFC's diagnostic allocator in the
first place.
RESOLUTION
These memory leaks can be safely ignored. The memory is correctly freed by
the Run-Time Library.
STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed
at the beginning of this article. This problem was fixed in Microsoft
Visual C++, 32-bit Edition, version 4.0.
| Modification Type: | Major | Last Reviewed: | 12/9/2003 |
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| Keywords: | kbbug kbfix KB130827 |
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