Automatic Casting from Near Pointer to Far Pointer

MS-DOS                 | OS/2       | WINDOWS

The information in this article applies to:

• The Microsoft C/C++ Compiler (CL.EXE) included with:

      - Microsoft C for MS-DOS, versions 6.0, 6.0a, and 6.0ax
      - Microsoft C for OS/2, versions 6.0, and 6.0a
      - Microsoft C/C++ for MS-DOS, version 7.0
      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
  

SUMMARY

In Microsoft C, near pointers are automatically cast to far pointers when a near to far conversion is required. In cases where near pointers are promoted to far pointers, the segment is the same as DGROUP. In cases where functions are prototyped to accept a far pointer, no explicit conversion is required.

MORE INFORMATION

Two of the cases of the automatic casting are shown in the sample code below:

Sample Code

/* Compile options needed: /AS or /AM in order to get
                           malloc() mapped to _nmalloc()
*/

#include <stdio.h>
#include <malloc.h>

void FuncName (char far *) ;
void main (void)

   char far * lpChar ;
   char     * npChar ;

   lpChar = malloc( 100 );   /* malloc is mapped to _nmalloc,
                             ** and returns near pointer, automatic
                             ** casting is performed with assignment.
                             ** Segment is DS. */

   npChar = malloc( 100 );

   printf("In main()\n");
   printf("npChar = %p\n", npChar);
   printf("lpChar = %Fp\n\n", lpChar);

   FuncName( npChar ) ;      /* npChar is converted to a far pointer
                             ** with the segment address to be DS */
}

void FuncName (char far * p)

   printf("In function FuncName()\n");
   printf("p = %Fp\n", p);