ID Number: Q11910
4.00 5.00 5.10 6.00 | 5.10 6.00
MS-DOS | OS/2
SYMPTOMS
When trying to get the length of a text string, using the SIZE
operator can produce undesired results. In the example below,
MSG_LEN is set to a value of 1, but it seems it should be set
to a value of 11:
MSG DB 'Darth Vader'
MSG_LEN EQU SIZE MSG
CAUSE
The value of MSG_LEN should be 1. The SIZE operator is defined to be
the LENGTH * TYPE as stated in the documentation. The expression,
LENGTH MSG, will be equal to 1 (when applied to a data label,
the LENGTH operator returns the number of elements created by the
DUP operator; otherwise it returns 1) and the expression, TYPE MSG,
will be equal to 1. Therefore, the variable MSG_LEN will be equal to 1.
RESOLUTION
In Macro Assembler version 6.00, the SIZEOF operator can be used to
calulate the total number of bytes allocated to a data item. In versions
prior to 6.00, a simple way to calculate the value you want is as
follows:
MSG DB 'Darth Vader'
MSG_LEN EQU $-MSG