DOCUMENT:Q67795  08-OCT-1999  [utilities]
TITLE   :EXE File Checksum Incorrect If LINK /CO or /E Option Used
PRODUCT :Microsoft Programming Utilities
PROD/VER::
OPER/SYS:
KEYWORDS:kb16bitonly

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft LINK for MS-DOS 
 - Microsoft LINK for OS/2 
-------------------------------------------------------------------------------

SUMMARY
=======

According to "The MS-DOS Encyclopedia," an MS-DOS .EXE file contains a checksum
value in its .EXE file header. This checksum value should make the sum of all
words in the .EXE file equal FFFFh. However, if the LINK command line specifies
the /CODEVIEW or /EXEPACK options, LINK does not calculate the checksum
correctly. Because current versions of MS-DOS ignore this checksum, this does
not cause any noticeable problems.

Note that Microsoft LINK versions 5.3 and later do not compute a checksum value.
The reserved bytes in the .EXE header are set to zero.

MORE INFORMATION
================

The following code example calculates the checksum for a specified MS-DOS
executable file.

Sample Code
-----------

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

   main (int argc, char * argv[])
   {
      FILE * fp;
      unsigned int nxt = 0, sum = 0;
      unsigned char bl, bh;

      if (argc != 2)
         exit(-1);
      if ((fp = fopen(argv[1], "rb")) == NULL)
         exit(-1);
      while (!feof(fp))
      {
         bl = fgetc(fp);
         if (!feof(fp))
            bh = fgetc(fp);
         else
            {
            bl = 0;
            bh = 0;
            }
         sum = sum + nxt;
         nxt = (unsigned int)bh * 256U + (unsigned int)bl;
      }
      nxt &= 0xFF;
      sum += nxt;
      printf("sum = %X\n", sum);
   }

Additional query words: kbinf 3.x 4.0x 4.10 5.0x 5.10 5.13 5.1x LinkIss

======================================================================
Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbZNotKeyword3 kbLINKSearch
Version           : :

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