Creating a Pointer to a Specific Memory Address

MS-DOS                      | WINDOWS

The information in this article applies to:

• Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, and 6.0ax
• Microsoft C/C++ for MS-DOS, version 7.0
• Microsoft Visual C++ for Windows, versions 1.0 and 1.5

SUMMARY

An application can create a pointer to access a specific address in memory with the FP_SEG and FP_OFF macros or by creating a far pointer in a long value.

MORE INFORMATION

The FP_SEG and FP_OFF macros are defined in the DOS.H header file. These macros can retrieve or specify the segment or offset in a far pointer.

The following code example demonstrates using the FP_SEG and FP_OFF macros to create a pointer to access video memory:

   char far *p;
   FP_SEG(p) = 0xb800;   // point to segment of video memory
   FP_OFF(p) = 0;        // set offset to first screen position

Another method to create a far pointer involves casting a long as a far pointer, as in the following example:

   p = (char far *)0xb8000000L;   // video memory