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Module String

module String: sig .. end
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.

val length : string -> int
Return the length (number of characters) of the given string.
val get : string -> int -> char
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 set : bytes -> int -> char -> unit
Deprecated.This is a deprecated alias of Bytes.set.
String.set s n c modifies byte sequence s in place, replacing the byte at index n with c. You can also write s.[n] <- c instead of String.set s n c.

Raise Invalid_argument if n is not a valid index in s.

val create : int -> bytes
Deprecated.This is a deprecated alias of Bytes.create.
String.create n returns a fresh byte sequence of length n. The sequence is uninitialized and contains arbitrary bytes.

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 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 copy : string -> string
Deprecated.Because strings are immutable, it doesn't make much sense to make identical copies of them.
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 : bytes -> int -> int -> char -> unit
Deprecated.This is a deprecated alias of Bytes.fill.
String.fill s start len c modifies byte sequence s in place, replacing len bytes with c, starting at start.

Raise Invalid_argument if start and len do not designate a valid range 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. If there is no special character in the argument, return the original string itself, not a copy. Its inverse function is Scanf.unescaped.

Raise Invalid_argument if the result is longer than Sys.max_string_length bytes.

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 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 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 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 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 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.