string.mli

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(*                                                                        *)
(*                                 OCaml                                  *)
(*                                                                        *)
(*             Xavier Leroy, projet Cristal, INRIA Rocquencourt           *)
(*                                                                        *)
(*   Copyright 1996 Institut National de Recherche en Informatique et     *)
(*     en Automatique.                                                    *)
(*                                                                        *)
(*   All rights reserved.  This file is distributed under the terms of    *)
(*   the GNU Lesser General Public License version 2.1, with the          *)
(*   special exception on linking described in the file LICENSE.          *)
(*                                                                        *)
(**************************************************************************)

(** String operations.

  A string is an immutable data structure that contains a
  fixed-length sequence of (single-byte) characters. Each character
  can be accessed in constant time through its index.

  Given a string [s] of length [l], we can access each of the [l]
  characters of [s] via its index in the sequence. Indexes start at
  [0], and we will call an index valid in [s] if it falls within the
  range [[0...l-1]] (inclusive). 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]]
  (inclusive). Note that the character at index [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 used to be modifiable in place, for instance via the
  {!String.set} and {!String.blit} functions described below. This
  usage is deprecated and only possible when the compiler is put in
  "unsafe-string" mode by giving the [-unsafe-string] command-line
  option (which is currently the default for reasons of backward
  compatibility). This is done by making the types [string] and
  [bytes] (see module {!Bytes}) interchangeable so that functions
  expecting byte sequences can also accept strings as arguments and
  modify them.

  All new code should avoid this feature and be compiled with the
  [-safe-string] command-line option to enforce the separation between
  the types [string] and [bytes].

 *)

external length : string -> int = "%string_length"
(** Return the length (number of characters) of the given string. *)

external get : string -> int -> char = "%string_safe_get"
(** [String.get s n] returns the character at index [n] in string [s].
   You can also write [s.[n]] instead of [String.get s n].

   Raise [Invalid_argument] if [n] not a valid index in [s]. *)




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 init : int -> (int -> char) -> string
(** [String.init n f] returns a string of length [n], with character
    [i] initialized to the result of [f i] (called in increasing
    index order).

    Raise [Invalid_argument] if [n < 0] or [n > ]{!Sys.max_string_length}.

    @since 4.02.0
*)


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 blit : string -> int -> bytes -> int -> int -> unit
(** Same as {!Bytes.blit_string}. *)

val concat : string -> string list -> string
(** [String.concat sep sl] concatenates the list of strings [sl],
    inserting the separator string [sep] between each.

    Raise [Invalid_argument] if the result is longer than
    {!Sys.max_string_length} bytes. *)

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] (in increasing index order) and stores the
    results in a new string that is returned.
    @since 4.00.0 *)

val mapi : (int -> char -> char) -> string -> string
(** [String.mapi f s] calls [f] with each character of [s] and its
    index (in increasing index order) and stores the results in a new
    string that is returned.
    @since 4.02.0 *)

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 neither 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.
    All characters outside the ASCII printable range (32..126) are
    escaped, as well as backslash and double-quote.

    If there is no special character in the argument that needs
    escaping, return the original string itself, not a copy.

    Raise [Invalid_argument] if the result is longer than
    {!Sys.max_string_length} bytes.

    The function {!Scanf.unescaped} is a left inverse of [escaped],
    i.e. [Scanf.unescaped (escaped s) = s] for any string [s] (unless
    [escape s] fails). *)

val index : string -> char -> int
(** [String.index s c] returns the index of the first
   occurrence of character [c] in string [s].

   Raise [Not_found] if [c] does not occur in [s]. *)

val index_opt: string -> char -> int option
(** [String.index_opt s c] returns the index of the first
    occurrence of character [c] in string [s], or
    [None] if [c] does not occur in [s].
    @since 4.05 *)

val rindex : string -> char -> int
(** [String.rindex s c] returns the index of the last
   occurrence of character [c] in string [s].

   Raise [Not_found] if [c] does not occur in [s]. *)

val rindex_opt: string -> char -> int option
(** [String.rindex_opt s c] returns the index of the last occurrence
    of character [c] in string [s], or [None] if [c] does not occur in
    [s].
    @since 4.05 *)

val index_from : string -> int -> char -> int
(** [String.index_from s i c] returns the index 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 index_from_opt: string -> int -> char -> int option
(** [String.index_from_opt s i c] returns the index of the
    first occurrence of character [c] in string [s] after position [i]
    or [None] if [c] does not occur in [s] after position [i].

    [String.index_opt s c] is equivalent to [String.index_from_opt s 0 c].
    Raise [Invalid_argument] if [i] is not a valid position in [s].

    @since 4.05
*)

val rindex_from : string -> int -> char -> int
(** [String.rindex_from s i c] returns the index 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 rindex_from_opt: string -> int -> char -> int option
(** [String.rindex_from_opt s i c] returns the index of the
   last occurrence of character [c] in string [s] before position [i+1]
   or [None] if [c] does not occur in [s] before position [i+1].

   [String.rindex_opt s c] is equivalent to
   [String.rindex_from_opt s (String.length s - 1) c].

   Raise [Invalid_argument] if [i+1] is not a valid position in [s].

    @since 4.05
*)

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_ascii : string -> string
(** Return a copy of the argument, with all lowercase letters
   translated to uppercase, using the US-ASCII character set.
   @since 4.03.0 *)

val lowercase_ascii : string -> string
(** Return a copy of the argument, with all uppercase letters
   translated to lowercase, using the US-ASCII character set.
   @since 4.03.0 *)

val capitalize_ascii : string -> string
(** Return a copy of the argument, with the first character set to uppercase,
   using the US-ASCII character set.
   @since 4.03.0 *)

val uncapitalize_ascii : string -> string
(** Return a copy of the argument, with the first character set to lowercase,
   using the US-ASCII character set.
   @since 4.03.0 *)

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}. *)

val equal: t -> t -> bool
(** The equal function for strings.
    @since 4.03.0 *)

val split_on_char: char -> string -> string list
(** [String.split_on_char sep s] returns the list of all (possibly empty)
    substrings of [s] that are delimited by the [sep] character.

    The function's output is specified by the following invariants:

    - The list is not empty.
    - Concatenating its elements using [sep] as a separator returns a
      string equal to the input ([String.concat (String.make 1 sep)
      (String.split_on_char sep s) = s]).
    - No string in the result contains the [sep] character.

    @since 4.04.0
*)

(**/**)

(* The following is for system use only. Do not call directly. *)

external unsafe_get : string -> int -> char = "%string_unsafe_get"