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Module String

module String: sig .. end
String operations.

Given a string s of length l, we call character number in s the index of a character in s. Indexes start at 0, and we will call a character number valid in s if it falls within the range [0...l-1]. A position is the point between two characters or at the beginning or end of the string. We call a position valid in s if it falls within the range [0...l]. Note that character number n is between positions n and n+1.

Two parameters start and len are said to designate a valid substring of s if len >= 0 and start and start+len are valid positions in s.

OCaml strings can be modified in place, for instance via the String.set and String.blit functions described below. This possibility should be used rarely and with much care, however, since both the OCaml compiler and most OCaml libraries share strings as if they were immutable, rather than copying them. In particular, string literals are shared: a single copy of the string is created at program loading time and returned by all evaluations of the string literal. Consider for example: 

      # let f () = "foo";;
      val f : unit -> string = <fun>
      # (f ()).[0] <- 'b';;
      - : unit = ()
      # f ();;
      - : string = "boo"

Likewise, many functions from the standard library can return string literals or one of their string arguments. Therefore, the returned strings must not be modified directly. If mutation is absolutely necessary, it should be performed on a fresh copy of the string, as produced by String.copy.

val length : string -> int
Return the length (number of characters) of the given string.
val get : string -> int -> char
String.get s n returns character number n in string s. You can also write s.[n] instead of String.get s n.

Raise Invalid_argument if n not a valid character number in s.

val set : string -> int -> char -> unit
String.set s n c modifies string s in place, replacing the character number n by c. You can also write s.[n] <- c instead of String.set s n c.

Raise Invalid_argument if n is not a valid character number in s.

val create : int -> string
String.create n returns a fresh string of length n. The string initially contains arbitrary characters.

Raise Invalid_argument if n < 0 or n > Sys.max_string_length.

val make : int -> char -> string
String.make n c returns a fresh string of length n, filled with the character c.

Raise Invalid_argument if n < 0 or n > Sys.max_string_length.

val copy : string -> string
Return a copy of the given string.
val sub : string -> int -> int -> string
String.sub s start len returns a fresh string of length len, containing the substring of s that starts at position start and has length len.

Raise Invalid_argument if start and len do not designate a valid substring of s.

val fill : string -> int -> int -> char -> unit
String.fill s start len c modifies string s in place, replacing len characters by c, starting at start.

Raise Invalid_argument if start and len do not designate a valid substring of s.

val blit : string -> int -> string -> int -> int -> unit
String.blit src srcoff dst dstoff len copies len characters from string src, starting at character number srcoff, to string dst, starting at character number dstoff. It works correctly even if src and dst are the same string, and the source and destination intervals overlap.

Raise Invalid_argument if srcoff and len do not designate a valid substring of src, or if dstoff and len do not designate a valid substring of dst.

val concat : string -> string list -> string
String.concat sep sl concatenates the list of strings sl, inserting the separator string sep between each.
val iter : (char -> unit) -> string -> unit
String.iter f s applies function f in turn to all the characters of s. It is equivalent to f s.[0]; f s.[1]; ...; f s.[String.length s - 1]; ().
val iteri : (int -> char -> unit) -> string -> unit
Same as String.iter, but the function is applied to the index of the element as first argument (counting from 0), and the character itself as second argument.
Since 4.00.0
val map : (char -> char) -> string -> string
String.map f s applies function f in turn to all the characters of s and stores the results in a new string that is returned.
Since 4.00.0
val trim : string -> string
Return a copy of the argument, without leading and trailing whitespace. The characters regarded as whitespace are: ' ', '\012', '\n', '\r', and '\t'. If there is no leading nor trailing whitespace character in the argument, return the original string itself, not a copy.
Since 4.00.0
val escaped : string -> string
Return a copy of the argument, with special characters represented by escape sequences, following the lexical conventions of OCaml. If there is no special character in the argument, return the original string itself, not a copy. Its inverse function is Scanf.unescaped.
val index : string -> char -> int
String.index s c returns the character number of the first occurrence of character c in string s.

Raise Not_found if c does not occur in s.

val rindex : string -> char -> int
String.rindex s c returns the character number of the last occurrence of character c in string s.

Raise Not_found if c does not occur in s.

val index_from : string -> int -> char -> int
String.index_from s i c returns the character number of the first occurrence of character c in string s after position i. String.index s c is equivalent to String.index_from s 0 c.

Raise Invalid_argument if i is not a valid position in s. Raise Not_found if c does not occur in s after position i.

val rindex_from : string -> int -> char -> int
String.rindex_from s i c returns the character number of the last occurrence of character c in string s before position i+1. String.rindex s c is equivalent to String.rindex_from s (String.length s - 1) c.

Raise Invalid_argument if i+1 is not a valid position in s. Raise Not_found if c does not occur in s before position i+1.

val contains : string -> char -> bool
String.contains s c tests if character c appears in the string s.
val contains_from : string -> int -> char -> bool
String.contains_from s start c tests if character c appears in s after position start. String.contains s c is equivalent to String.contains_from s 0 c.

Raise Invalid_argument if start is not a valid position in s.

val rcontains_from : string -> int -> char -> bool
String.rcontains_from s stop c tests if character c appears in s before position stop+1.

Raise Invalid_argument if stop < 0 or stop+1 is not a valid position in s.

val uppercase : string -> string
Return a copy of the argument, with all lowercase letters translated to uppercase, including accented letters of the ISO Latin-1 (8859-1) character set.
val lowercase : string -> string
Return a copy of the argument, with all uppercase letters translated to lowercase, including accented letters of the ISO Latin-1 (8859-1) character set.
val capitalize : string -> string
Return a copy of the argument, with the first character set to uppercase.
val uncapitalize : string -> string
Return a copy of the argument, with the first character set to lowercase.
type t = string
An alias for the type of strings.
val compare : t -> t -> int
The comparison function for strings, with the same specification as Pervasives.compare. Along with the type t, this function compare allows the module String to be passed as argument to the functors Set.Make and Map.Make.