PRB: _vmalloc Fails When Running 386MAX

The information in this article applies to:

• Microsoft C/C++ for MS-DOS, version 7.0
• Microsoft Visual C++ for Windows, versions 1.0 and 1.5

SYMPTOMS

The function 0Fh (Resize Memory Block) of the 386MAX XMS handler seems to always return a value indicating that there is not enough extended memory. This happens when 386MAX version 6.02 or an earlier version of the 386MAX memory manager is installed and the swaparea parameter to _vheapinit() contains only the _VM_XMS value.

CAUSE

The function 0Fh (Resize Memory Block) of the 386MAX XMS handler seems to always return a value indicating that there is not enough extended memory.

RESOLUTION

There are three ways to work around the problem:

• Bitwise OR (|) the third parameter of the _vheapinit call with either _VM_EMS or _VM_DISK. This will allow _vmalloc to access expanded memory or disk space.
• Substitute the 386MAX XMS handler with another. For example, run the program under Windows, or remove 386MAX and use HIMEM.SYS.
• Upgrade to 386MAX version 6.02b or later.

MORE INFORMATION

Sample Code

/* Compile options needed:    None
*/

#include <stdio.h>
#include <stdlib.h>
#include <vmemory.h>

void main()

   _vmhnd_t handle;

   if ( !_vheapinit( 0, _VM_ALLDOS, _VM_XMS) )
   {
      printf( "Could not initialize virtual memory manager.\n" );
      exit( -1 );
   }

   printf( "Requesting 100 bytes of virtual memory.\n" );
   if ( (handle = _vmalloc( 100 )) == _VM_NULL )
      {
      _vheapterm();
      printf("Allocation failed\n");
      exit( -1 );
      }

   _vheapterm();