function SubStr (S: String; FirstChar: Integer): String;
or
function SubStr (S: String; FirstChar, Count: Integer): String;
SubStr returns a sub-string of S starting with the character at position FirstChar. If Count is given, such many characters will be copied into the sub-string. If Count is omitted, the sub-string will range to the end of S.
If Count is too large for the sub-string to fit in S or if FirstChar exceeds the length of S, SubStr triggers a runtime error. (For a function returning the empty string instead, see Copy.)
SubStr is an ISO 10206 Extended Pascal extension.
program SubStrDemo; var S: String (42); begin S := 'Hello'; WriteLn (SubStr (S, 2, 3)); { yields `ell' } WriteLn (SubStr (S, 3)); { yields `llo' } WriteLn (SubStr (S, 4, 7)); { yields a runtime error } WriteLn (SubStr (S, 42)); { yields a runtime error } end.