module String:sig..end
Strings.
A string s of length n is an indexable and immutable sequence
of n bytes. For historical reasons these bytes are referred to
as characters.
The semantics of string functions is defined in terms of indices and positions. These are depicted and described as follows.
positions 0 1 2 3 4 n-1 n
+---+---+---+---+ +-----+
indices | 0 | 1 | 2 | 3 | ... | n-1 |
+---+---+---+---+ +-----+i of s is an integer in the range [0;n-1].
It represents the ith byte (character) of s which can be
accessed using the constant time string indexing operator
s.[i].i of s is an integer in the range
[0;n]. It represents either the point at the beginning of
the string, or the point between two indices, or the point at
the end of the string. The ith byte index is between position
i and i+1.Two integers start and len are said to define a valid
substring of s if len >= 0 and start, start+len are
positions of s.
Unicode text. Strings being arbitrary sequences of bytes, they
can hold any kind of textual encoding. However the recommended
encoding for storing Unicode text in OCaml strings is UTF-8. This
is the encoding used by Unicode escapes in string literals. For
example the string "\u{1F42B}" is the UTF-8 encoding of the
Unicode character U+1F42B.
Past mutability. Before OCaml 4.02, strings used to be modifiable in
place like Bytes.t mutable sequences of bytes.
OCaml 4 had various compiler flags and configuration options to support the
transition period from mutable to immutable strings.
Those options are no longer available, and strings are now always
immutable.
The labeled version of this module can be used as described in the
StdLabels module.
typet =string
The type for strings.
val make : int -> char -> stringmake n c is a string of length n with each index holding the
character c.
Invalid_argument if n < 0 or n > Sys.max_string_length.val init : int -> (int -> char) -> stringinit n f is a string of length n with index
i holding the character f i (called in increasing index order).
Invalid_argument if n < 0 or n > Sys.max_string_length.val empty : stringThe empty string.
val length : string -> intlength s is the length (number of bytes/characters) of s.
val get : string -> int -> charget s i is the character at index i in s. This is the same
as writing s.[i].
Invalid_argument if i not an index of s.val of_bytes : bytes -> stringReturn a new string that contains the same bytes as the given byte sequence.
val to_bytes : string -> bytesReturn a new byte sequence that contains the same bytes as the given string.
val blit : string -> int -> bytes -> int -> int -> unitSame as Bytes.blit_string which should be preferred.
Note. The (^) binary operator concatenates two
strings.
val concat : string -> string list -> stringconcat sep ss concatenates the list of strings ss, inserting
the separator string sep between each.
Invalid_argument if the result is longer than
Sys.max_string_length bytes.val cat : string -> string -> stringcat s1 s2 concatenates s1 and s2 (s1 ^ s2).
Invalid_argument if the result is longer than
Sys.max_string_length bytes.val equal : t -> t -> boolequal s0 s1 is true if and only if s0 and s1 are character-wise
equal.
val compare : t -> t -> intcompare s0 s1 sorts s0 and s1 in lexicographical order. compare
behaves like compare on strings but may be more efficient.
val starts_with : prefix:string -> string -> boolstarts_with ~prefix s is true if and only if s starts with
prefix.
val ends_with : suffix:string -> string -> boolends_with ~suffix s is true if and only if s ends with suffix.
val contains_from : string -> int -> char -> boolcontains_from s start c is true if and only if c appears in s
after position start.
Invalid_argument if start is not a valid position in s.val rcontains_from : string -> int -> char -> boolrcontains_from s stop c is true if and only if c appears in s
before position stop+1.
Invalid_argument if stop < 0 or stop+1 is not a valid
position in s.val contains : string -> char -> boolcontains s c is String.contains_from s 0 c.
val sub : string -> int -> int -> stringsub s pos len is a string of length len, containing the
substring of s that starts at position pos and has length
len.
Invalid_argument if pos and len do not designate a valid
substring of s.val split_on_char : char -> string -> string listsplit_on_char sep s is the list of all (possibly empty)
substrings of s that are delimited by the character sep.
The function's result is specified by the following invariants:
sep as a separator returns a
string equal to the input (concat (make 1 sep)
(split_on_char sep s) = s).sep character.val map : (char -> char) -> string -> stringmap f s is the string resulting from applying f to all the
characters of s in increasing order.
val mapi : (int -> char -> char) -> string -> stringmapi f s is like String.map but the index of the character is also
passed to f.
val fold_left : ('acc -> char -> 'acc) -> 'acc -> string -> 'accfold_left f x s computes f (... (f (f x s.[0]) s.[1]) ...) s.[n-1],
where n is the length of the string s.
val fold_right : (char -> 'acc -> 'acc) -> string -> 'acc -> 'accfold_right f s x computes f s.[0] (f s.[1] ( ... (f s.[n-1] x) ...)),
where n is the length of the string s.
val for_all : (char -> bool) -> string -> boolfor_all p s checks if all characters in s satisfy the predicate p.
val exists : (char -> bool) -> string -> boolexists p s checks if at least one character of s satisfies the predicate
p.
val trim : string -> stringtrim s is s without leading and trailing whitespace. Whitespace
characters are: ' ', '\x0C' (form feed), '\n', '\r', and '\t'.
val escaped : string -> stringescaped s is s with special characters represented by escape
sequences, following the lexical conventions of OCaml.
All characters outside the US-ASCII printable range [0x20;0x7E] are escaped, as well as backslash (0x2F) and double-quote (0x22).
The function Scanf.unescaped is a left inverse of escaped,
i.e. Scanf.unescaped (escaped s) = s for any string s (unless
escaped s fails).
Invalid_argument if the result is longer than
Sys.max_string_length bytes.val uppercase_ascii : string -> stringuppercase_ascii s is s with all lowercase letters
translated to uppercase, using the US-ASCII character set.
val lowercase_ascii : string -> stringlowercase_ascii s is s with all uppercase letters translated
to lowercase, using the US-ASCII character set.
val capitalize_ascii : string -> stringcapitalize_ascii s is s with the first character set to
uppercase, using the US-ASCII character set.
val uncapitalize_ascii : string -> stringuncapitalize_ascii s is s with the first character set to lowercase,
using the US-ASCII character set.
val iter : (char -> unit) -> string -> unititer 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.[length s - 1]; ().
val iteri : (int -> char -> unit) -> string -> unititeri is like String.iter, but the function is also given the
corresponding character index.
val index_from : string -> int -> char -> intindex_from s i c is the index of the first occurrence of c in
s after position i.
Not_found if c does not occur in s after position i.Invalid_argument if i is not a valid position in s.val index_from_opt : string -> int -> char -> int optionindex_from_opt s i c is the index of the first occurrence of c
in s after position i (if any).
Invalid_argument if i is not a valid position in s.val rindex_from : string -> int -> char -> intrindex_from s i c is the index of the last occurrence of c in
s before position i+1.
Not_found if c does not occur in s before position i+1.Invalid_argument if i+1 is not a valid position in s.val rindex_from_opt : string -> int -> char -> int optionrindex_from_opt s i c is the index of the last occurrence of c
in s before position i+1 (if any).
Invalid_argument if i+1 is not a valid position in s.val index : string -> char -> intindex s c is String.index_from s 0 c.
val index_opt : string -> char -> int optionindex_opt s c is String.index_from_opt s 0 c.
val rindex : string -> char -> intrindex s c is String.rindex_from s (length s - 1) c.
val rindex_opt : string -> char -> int optionrindex_opt s c is String.rindex_from_opt s (length s - 1) c.
val to_seq : t -> char Seq.tto_seq s is a sequence made of the string's characters in
increasing order. In "unsafe-string" mode, modifications of the string
during iteration will be reflected in the sequence.
val to_seqi : t -> (int * char) Seq.tto_seqi s is like String.to_seq but also tuples the corresponding index.
val of_seq : char Seq.t -> tof_seq s is a string made of the sequence's characters.
val get_utf_8_uchar : t -> int -> Uchar.utf_decodeget_utf_8_uchar b i decodes an UTF-8 character at index i in
b.
val is_valid_utf_8 : t -> boolis_valid_utf_8 b is true if and only if b contains valid
UTF-8 data.
val get_utf_16be_uchar : t -> int -> Uchar.utf_decodeget_utf_16be_uchar b i decodes an UTF-16BE character at index
i in b.
val is_valid_utf_16be : t -> boolis_valid_utf_16be b is true if and only if b contains valid
UTF-16BE data.
val get_utf_16le_uchar : t -> int -> Uchar.utf_decodeget_utf_16le_uchar b i decodes an UTF-16LE character at index
i in b.
val is_valid_utf_16le : t -> boolis_valid_utf_16le b is true if and only if b contains valid
UTF-16LE data.
The functions in this section binary decode integers from strings.
All following functions raise Invalid_argument if the characters
needed at index i to decode the integer are not available.
Little-endian (resp. big-endian) encoding means that least
(resp. most) significant bytes are stored first. Big-endian is
also known as network byte order. Native-endian encoding is
either little-endian or big-endian depending on Sys.big_endian.
32-bit and 64-bit integers are represented by the int32 and
int64 types, which can be interpreted either as signed or
unsigned numbers.
8-bit and 16-bit integers are represented by the int type,
which has more bits than the binary encoding. These extra bits
are sign-extended (or zero-extended) for functions which decode 8-bit
or 16-bit integers and represented them with int values.
val get_uint8 : string -> int -> intget_uint8 b i is b's unsigned 8-bit integer starting at character
index i.
val get_int8 : string -> int -> intget_int8 b i is b's signed 8-bit integer starting at character
index i.
val get_uint16_ne : string -> int -> intget_uint16_ne b i is b's native-endian unsigned 16-bit integer
starting at character index i.
val get_uint16_be : string -> int -> intget_uint16_be b i is b's big-endian unsigned 16-bit integer
starting at character index i.
val get_uint16_le : string -> int -> intget_uint16_le b i is b's little-endian unsigned 16-bit integer
starting at character index i.
val get_int16_ne : string -> int -> intget_int16_ne b i is b's native-endian signed 16-bit integer
starting at character index i.
val get_int16_be : string -> int -> intget_int16_be b i is b's big-endian signed 16-bit integer
starting at character index i.
val get_int16_le : string -> int -> intget_int16_le b i is b's little-endian signed 16-bit integer
starting at character index i.
val get_int32_ne : string -> int -> int32get_int32_ne b i is b's native-endian 32-bit integer
starting at character index i.
val hash : t -> intAn unseeded hash function for strings, with the same output value as
Hashtbl.hash. This function allows this module to be passed as argument
to the functor Hashtbl.Make.
val seeded_hash : int -> t -> intA seeded hash function for strings, with the same output value as
Hashtbl.seeded_hash. This function allows this module to be passed as
argument to the functor Hashtbl.MakeSeeded.
val get_int32_be : string -> int -> int32get_int32_be b i is b's big-endian 32-bit integer
starting at character index i.
val get_int32_le : string -> int -> int32get_int32_le b i is b's little-endian 32-bit integer
starting at character index i.
val get_int64_ne : string -> int -> int64get_int64_ne b i is b's native-endian 64-bit integer
starting at character index i.
val get_int64_be : string -> int -> int64get_int64_be b i is b's big-endian 64-bit integer
starting at character index i.
val get_int64_le : string -> int -> int64get_int64_le b i is b's little-endian 64-bit integer
starting at character index i.