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The latest version of this topic can be found at LOCAL (MASM).

In the first directive, within a macro, LOCAL defines labels that are unique to each instance of the macro.

      LOCAL localname [[, localname]]...  
LOCAL label [[ [count ] ]] [[:type]] [[, label [[ [count] ]] [[type]]]]...  

In the second directive, within a procedure definition (PROC), LOCAL creates stack-based variables that exist for the duration of the procedure. The label may be a simple variable or an array containing count elements.

Directives Reference