PRB: Comparison of a Constant and a Relocatable Is Not Allowed (35114)

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