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NUL Operator

When a formal parameter is omitted from a macro invocation, it is assigned a value of NULL. You can check for NULL parameters by using the NUL operator in an IF control statement in the macro.

The NUL operator requires an argument. If no argument is found, NUL returns a value of 0.

For example:

        IF NUL X

EXAMPLE            ; Invoke the macro with no parameters
;Nothing is output since the macro exits (because the x parameter is NULL)


  • A blank character (' ') has an ASCII value of 20h and is not equivalent to a NULL.
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