Q30424: Using the & Operator to Combine Multiple Parameters

Article: Q30424
Product(s): Microsoft Macro Assembler
Version(s): 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 6.0, 6.0a, 6.0b 
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SUMMARY
=======

Attempting to use the & substitute operator to combine parameters requires
that each parameter being substituted have one ampersand on the left and right.
If an ampersand is adjacent to white space, it can be omitted as long as one
ampersand is next to each parameter to be substituted.

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

If multiple parameters are being combined with the & operator, each
parameter must have it's own & symbol associated with it. Also each &
symbol can only be associated with one parameter. The sample code provided below
helps to illustrate the use of the & substitute operator to combine multiple
parameters.

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

  ; Assemble options needed: none

  .MODEL small, c
  .STACK

  level1 macro
          forc x,f
              level2 x
          endm
      endm

  level2 macro x
          forc y,e
              level3 x&y
          endm
      endm

  level3 macro i
  level3&i:
      push bp
      mov  bp, 0&i&h
      jmp  FINISH
      endm

  .CODE

  START:
      level1
  FINISH:
      mov   ax, 4C00h
      int   21h
  end START

Attempting to assemble the sample code given above will cause MASM 6.0 to
generate the following error messages:

  

   file.asm(27): error A2048: nondigit in number
    level3(3): Macro Called From
     MacroLoop(1): iteration 1: Macro Called From
      level2(3): Macro Called From
       MacroLoop(1): iteration 1: Macro Called From
        level1(3): Macro Called From
         file.asm(27): Main Line Code

MASM generates the following code for the macros in the sample code:

      level1
          forc x,f
          level2 x
      endm
      level2 f
          forc y,e
          level3 fy
      endm
      level3 fy
          level3fy:
          push bp
          mov bp,0fyh

The A2048 error is generated because the substitution of the 'y' parameter being
performed in the call to the level3 macro from inside the level2 macro is not
occurring. The A2048 error is generated when the level3 macro attempts to store
the invalid value it was passed from the level2 macro in the BP register.

The substitution of the 'y' parameter is not occurring because the syntax being
used with the & operator is incorrect. The level2 macro is defined as
follows:

  level2 macro x
          forc y,e
              level3 x&y
          endm
      endm

To allow the correct substitution to take place, add another & to the level3
macro call, like this:

  level2 macro x
          forc y,e
              level3 x&&y
          endm
      endm

After making the change shown above, MASM 6.0 then generates the following code
for the macros:

      level1
          forc x,f
          level2 x
      endm
      level2 f
          forc y,e
          level3 f&y
      endm
      level3 fe
          level3fe:
          push bp
          mov bp,0feh
          jmp FINISH

The value being placed into the BP register is now valid and the code functions
as expected.

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

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

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