Q35128: PRB: Line Parsing Order: Looks Up Second Token First

Article: Q35128
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 example below will generate the warning:

  warning A4016: Reserved word used as symbol: MOV

when assembled with Microsoft Macro Assembler (MASM) 5.1 and 5.1a. This warning
is misleading. MASM 6.0, 6.0a, and 6.0b generate the more specific error
message:

  error A2001: immediate operand not allowed

CAUSE
=====

The reference to a_struc.a in the example below is a reference to a structure
template and not to a variable stored in memory. Thus, a_struc.a is a constant
or immediate operand. MASM 5.1 and 5.1a always looks up the second token on the
line first. In the case below, it sees "a_struc". Because a_struc is a structure
declaration, MASM assumes the line declares a structure instance with "MOV"
being the label. At this point, MASM errors on trying to use reserved symbol
"MOV" as a structure instance label.

RESOLUTION
==========

This is the expected behavior of MASM.

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

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

  ; Assemble options needed: none

  a_struc STRUC
      a DW ?
  a_struc ENDS

  _TEXT SEGMENT 'CODE'
  ASSUME CS:_TEXT
  start:
      mov a_struc.a, ax
      mov ax, 4C00h
      int 21h
  _TEXT ENDS

  END start

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

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

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