INFO: A Case Where BUFF[] and *BUFF Are Different

 Last reviewed: October 7, 1997
Article ID: Q38024
The information in this article applies to:
  • Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax
  • Microsoft C/C++ for MS-DOS, version 7.0
  • Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52
  • Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

When the variable buff has been declared in an assembly-language program, such as the following 

        .data
        public buff
_buff   db 200 dup (0xab)
        .data ends
there is a difference between the two following C declarations: 

   extern unsigned char buff[];

   extern unsigned *buff;
The difference is that the first declaration says there is a block of memory that is named buff; the second says there is something called buff that is a pointer.

This difference can be seen by referencing buff as follows: 

   buff[x]
If buff is declared as an array, the referencing is correct.

However, if buff is declared as a pointer, the referencing is incorrect. The data pointed to by buff (ab in this example) is translated into a memory address, then x bytes are added to it generating an incorrect reference.

For additional information, please see the following article(s) in the Microsoft Knowledge Base: 

   ARTICLE-ID: Q44463
   TITLE     : Difference Between Arrays and Pointers in C

Keywords          : CLngIss kbfasttip
Version           : MS- DOS:5.1,6.0,6.00a,6.00ax,7.0;WIN3X:1.0,1.5,1.51,1.52;WINNT:1.0,2.0,2.1,4.0, 5.0;
Platform          : MS-DOS NT WINDOWS
Issue type        : kbinfo

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Last reviewed: October 7, 1997
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