Using the & Operator to Combine Multiple Parameters

ID: Q30424

The information in this article applies to:

Microsoft Macro Assembler for MS-DOS, versions 6.0, 6.0a, 6.0b

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

Keywords :
Version : :6.0,6.0a,6.0b
Platform :
Issue type :