How to Access & Modify Memory in MS-DOS from a C Program

MS-DOS                 | WINDOWS

The information in this article applies to:

• Microsoft C for MS-DOS, versions 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

The code example below contains two functions to access memory in an application developed for the MS-DOS operating system. The peek() function provides access to a memory location and the poke() function allows an application to specify the value for a memory location.

MORE INFORMATION

Sample Code

/*
 * Compile options needed: None
 */

// The following function places a value into the specified
// memory location segment:offset

void poke(unsigned int segment, unsigned int offset,
          unsigned char val)
{
   unsigned char far *ptr;

   ptr = (unsigned char far *)(((long)segment << 16) | (long)offset);
   *ptr = val;

// The following function returns the contents of the specified
// memory location segment:offset

   unsigned char far *ptr;

   ptr = (unsigned char far *)(((long)segment << 16) | (long)offset);
   return *ptr;