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substring(+String1, +String2, ?Position)

Succeeds if String2 is a substring of String1 beginning at position Position.
String1
String.
String2
String.
Position
Integer or variable.

Description

Used to test that String2 is a substring of String1 beginning at position Position. In this case, String1 and String2 are strings and Position is an integer.

Also used to find the first position in String1 that its substring String2 begins. In this case, String1 and String2 are strings and Position is a variable.

String positions must be positive and start at 1.

Modes and Determinism

Fail Conditions

Fails if String2 is not a substring of String1 beginning at position Position

Exceptions

(4) instantiation fault
Either String1 or String2 (or both) are not instantiated.
(5) type error
Either String1 or String2 (or both) are instantiated, but not to strings.
(5) type error
Position is neither an integer nor a variable.
(6) out of range
Position is not a positive integer.

Examples

Success:
      substring("str","st",1).
      substring("abcabcabc","bc",X)     (gives X=2).
      substring("abcabcabc","bc",8).
      substring("abc","",X).            (gives X=1).
      substring("abc","",2).
Fail:
      substring("astring","strg",2).
      substring("","a",X).
Error:
      substring(S,"str",1).             (Error 4).
      substring('str',S,1).             (Error 5).
      substring("st","s",1.0).          (Error 5).
      substring("ab","a",-2).           (Error 6).

See Also

substring / 5, split_string / 4