
substring(+String1, ?Position, ?Length, ?String2)

   Succeeds if String2 is the substring of String1 starting at position
Position and of length Length.



Arguments
   +String1            String.
   ?Position           Integer (from 1 upwards) or variable.
   ?Length             Integer (from 0 upwards) or variable.
   ?String2            String or variable.

Type
   Strings and Atoms

Description
   Succeeds if String2 is a substring of String1 starting at position
   Position and of length Length.


   On backtracking, all such substrings are found.


   The first character of a string is at position 1.


Note
   If String1 and String2 are instantiated, it is more efficient to use the
   predicates substring/3 and/or string_length/2.




Resatisfiable
      Yes.

Fail Conditions
      Fails if String2 is not a substring of String1, or if Length is not the
   length of String2, or if String2 does not begin at position Position.



Exceptions
     5 --- String1 is instantiated, but not to a string.
     5 --- String2 is neither a string nor a variable.
     5 --- Either (or both) of Position or Length are neither integers    nor variables.
     4 --- String1 is not instantiated.

Examples
   
Success:
  substring("abcabc",3,1,"c").
  substring("abcabc",6,1,"c").
  substring("abcabc",P,1,"c"). (gives P=3; P=6).
  substring("abcabc",3,3,S).   (gives S="cab").
  substring("abc",P,L,"b").    (gives P=2, L=1).

  [eclipse]: substring("ab",P,1,S).
  P=1
  S="a"     More? (;)
  P=2
  S="b"
  yes.

  [eclipse]: substring("ab",1,L,S).
  L=0
  S=""      More? (;)
  L=1
  S="a"     More? (;)
  L=2
  S="ab"
  yes,

  [eclipse]: substring("ab",P,L,S), writeq((P,L,S)), nl, fail.
  1 , 0 , ""            % on backtracking, returns all
  1 , 1 , "a"           %   substrings of String1.
  1 , 2 , "ab"
  2 , 0 , ""
  2 , 1 , "b"
  3 , 0 , ""
  no (more) solution.

Fail:
  substring("joey",P,L,"joy").
  substring("joey",P,2,"joe").

Error:
  substring(S1,P,L,S2).                (Error 4).
  substring(S1,1,2,"bc").              (Error 4).
  substring(S1,1,2,'str').             (Error 4).
  substring('string',2,3,S2).          (Error 5).
  substring("string",2,3,'str').       (Error 5).





See Also
   substring / 3, string_length / 2, split_string / 4
