This is part of Family API which allow to create dual-os version of program runs under OS/2 and DOS

Note: This is legacy API call. It is recommended to use 32-bit equivalent

2021/09/17 04:47 · prokushev · 0 Comments
2021/08/20 03:18 · prokushev · 0 Comments


This call changes the size of memory originally allocated by DosAllocHuge.


DosReallocHuge (NumSeg, Size, Selector)


  • NumSeg (USHORT) - input : Number of 65536 byte segments requested.
  • Size (USHORT) - input : Number of bytes requested in the last non-65536 byte segment. A value of 0 indicates none.
  • Selector (SEL) - input : Selector returned on a previous DosAllocHuge.

Return Code

rc (USHORT) - return

Return code descriptions are:

  • 0 NO_ERRORç


DosReallocHuge is called to change the size of unshared or shared huge memory allocated by DosAllocHuge. The selector used for this call must be the one returned by the DosAllocHuge request.

Normally, segments allocated as shared (AllocFlags bits 0 and 1 were set) cannot be decreased in size. However, if AllocFlags bit 3 was also set, the shared segment's size can be decreased.

DosReallocHuge is also called to reallocate a segment allocated as discardable (AllocFlags bit 2 set) after the segment is discarded by the system. The call to DosReallocHuge automatically locks the segment for access by the caller, the same as if a DosLockSeg had been issued.

'Note:' This request may be issued from privilege level 2 or 3. However, only a privilege level 3 huge segment is valid.

Family API Considerations

Some options operate differently in the DOS mode than in the OS/2 mode. Therefore, the following restriction applies to DosReallocHuge when coding for the DOS mode:

The requested Size value is rounded up to the next paragraph (16-byte).


C Binding

USHORT  rc = DosReallocHuge(NumSeg, Size, Selector);
USHORT           NumSeg;        /* Number of 65536-byte segments
                                    requested */
USHORT           Size;          /* Number of bytes in last segment */
SEL              Selector;      /* Selector */
USHORT           rc;            /* return code */

MASM Binding

EXTRN  DosReallocHuge:FAR
PUSH   WORD    NumSeg        ;Number of 65536-byte segments requested
PUSH   WORD    Size          ;Number of bytes in last segment
PUSH   WORD    Selector      ;Selector
CALL   DosReallocHuge
Returns WORD