FIX: App Terminates Unexpectedly after Windows NT 3.51 Upgrade

The information in this article applies to:

• The C Run-time (CRT) included with: Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1, 2.2

SYMPTOMS

After you upgrade to Windows NT version 3.51, malloc or other run-time memory allocation functions may fail when unable to grow the run-time library's heap.

Windows applications that are statically linked to the C run-time library and all console applications issue the error, "R6018 - Unexpected heap error," and terminate.

Windows-based applications which are linked to the DLL version of the C run- time library, and MFC applications will unexpectedly terminate with no error message. This termination may be preceded by a message saying that the system is low on resources and to close down some applications.

CAUSE

This problem is caused by a change in the return code from the VirtualAlloc() function. It formerly returned ERROR_NOT_ENOUGH_MEMORY when it could not commit pages. Now it returns ERROR_COMMITMENT_LIMIT. The problem occurs only on Windows NT version 3.51 and only when the application hits its commit limit as chosen by Windows NT. This limit varies depending on such things as the size of the installed memory and the number of applications running. The sample code listed in this article causes the R6018 error when run on Windows NT version 3.51 but runs to completion under previous versions of Windows NT.

RESOLUTION

The C Run-Time heap manager was changed in Visual C++ 4.0 to no longer use VirtualAlloc(). Visual C++ version 4.0 correctly handles the ERROR_COMMITMENT_LIMIT case.

This problem can be worked-around in Visual C++ 2.X by allocating large blocks of memory using Win32 memory allocation APIs.

STATUS

Microsoft has confirmed this to be a problem when using malloc on Windows NT version 3.51. This problem was corrected in Visual C++, 32-bit edition, version 4.0.

MORE INFORMATION

Sample Code to Reproduce Problem

/* Compile options needed: none
*/

#include <stdlib.h>
void main()

    void * p = malloc( 1024*1024*1024 ); // try to allocate 1GB
    if( p )
    {
        printf( "malloc returned non-NULL\r\n");
        free(p);
    }
    else
        printf( "malloc returned NULL\r\n");
}