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Q35114: PRB: Comparison of a Constant and a Relocatable Is Not Allowed

Article: Q35114
Product(s): Microsoft Macro Assembler
Version(s): 5.1,5.1a,6.0,6.0a,6.0b
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), versions 5.1, 5.1a, 6.0, 6.0a, 6.0b 
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SYMPTOMS
========

The comparison of a constant and a relocatable is not allowed. The following
example demonstrates three approaches to comparing a constant and a relocatable.
In the Microsoft Macro Assembler (MASM) 5.1 and 5.1a you will get the warning:

  warning A4031: Operand types must match

on the first of these approaches. In MASM 6.0, 6.0a, and 6.0b you will get the
error:

  error A2026: constant expected

on the first of these approaches, and you will get the error:

  error A2094: operand must be relocatable

on the second. The third approach, which turns the relocatable into a constant by
subtracting the beginning of the segment, will work.

CAUSE
=====

You can not compare a constant to a relocatable at assembly time because the
linker may change the value of the relocatable at link time.

RESOLUTION
==========

This is the expected behavior of MASM. The third approach in the example below
demonstrates the prefered way to compare a constant and a relocatable.

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

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

  ; Assemble options needed: none

  _DATA SEGMENT 'DATA'

  a_var DW ?

  .ERRNZ 08000h LT a_var          ; constant LT relocatable
  .ERRNZ _DATA:08000h LT a_var    ; cast constant to relocatable
  .ERRNZ 08000h LT a_var- @CurSeg ; difference of relocatables

  _DATA ENDS

  END

Additional query words: 5.10 5.10a 6.00 6.00a 6.00b

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM600 kbMASM600a kbMASM510a kbMASM600b
Version           : :5.1,5.1a,6.0,6.0a,6.0b

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