I have a question regarding define directive in preprocessor.

How can I replace/define a string with another string ?
It's about mod operator, some assemblers use % for mod operator.
But % could be used in another context (for defining binary values).



This example works but is problematic when % used in another context.
I tried to replace the string " % " with one leading and one trailing space but FASM throws error "invalid name".



Does anybody know how to realize this ?

You could use "% fix mod" but % has special meanings in FASM when used with other directives such as repeat.

No, it is not possible to have strict textual replacements done by fasm's preprocessor, because it does not operate on original source text, but on the pre-tokenized data. You may find details of this process explained in Understanding fasm article.