Provided by: ocaml-man_5.3.0-2_all 
NAME
StringLabels - Strings.
Module
Module StringLabels
Documentation
Module StringLabels
: 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 | +---+---+---+---+ +-----+
-An index i of s is an integer in the range [ 0 ; n-1 ]. It represents the i th byte (character) of s
which can be accessed using the constant time string indexing operator s.[i] .
-A position 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 i th 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.
Strings
type t = string
The type for strings.
val make : int -> char -> string
make n c is a string of length n with each index holding the character c .
Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
val init : int -> f:(int -> char) -> string
init n ~f is a string of length n with index i holding the character f i (called in increasing index
order).
Since 4.02
Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
val empty : string
The empty string.
Since 4.13
val length : string -> int
length s is the length (number of bytes/characters) of s .
val get : string -> int -> char
get s i is the character at index i in s . This is the same as writing s.[i] .
Raises Invalid_argument if i not an index of s .
val of_bytes : bytes -> string
Return a new string that contains the same bytes as the given byte sequence.
Since 4.13
val to_bytes : string -> bytes
Return a new byte sequence that contains the same bytes as the given string.
Since 4.13
val blit : src:string -> src_pos:int -> dst:bytes -> dst_pos:int -> len:int -> unit
Same as Bytes.blit_string which should be preferred.
Concatenating
Note. The (^) binary operator concatenates two strings.
val concat : sep:string -> string list -> string
concat ~sep ss concatenates the list of strings ss , inserting the separator string sep between each.
Raises Invalid_argument if the result is longer than Sys.max_string_length bytes.
val cat : string -> string -> string
cat s1 s2 concatenates s1 and s2 ( s1 ^ s2 ).
Since 4.13
Raises Invalid_argument if the result is longer than Sys.max_string_length bytes.
Predicates and comparisons
val equal : t -> t -> bool
equal s0 s1 is true if and only if s0 and s1 are character-wise equal.
Since 4.05
val compare : t -> t -> int
compare 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 -> bool
starts_with ~prefix s is true if and only if s starts with prefix .
Since 4.13
val ends_with : suffix:string -> string -> bool
ends_with ~suffix s is true if and only if s ends with suffix .
Since 4.13
val contains_from : string -> int -> char -> bool
contains_from s start c is true if and only if c appears in s after position start .
Raises Invalid_argument if start is not a valid position in s .
val rcontains_from : string -> int -> char -> bool
rcontains_from s stop c is true if and only if c appears in s before position stop+1 .
Raises Invalid_argument if stop < 0 or stop+1 is not a valid position in s .
val contains : string -> char -> bool
contains s c is String.contains_from s 0 c .
Extracting substrings
val sub : string -> pos:int -> len:int -> string
sub s ~pos ~len is a string of length len , containing the substring of s that starts at position pos and
has length len .
Raises Invalid_argument if pos and len do not designate a valid substring of s .
val split_on_char : sep:char -> string -> string list
split_on_char ~sep s is the list of all (possibly empty) substrings of s that are delimited by the
character sep . If s is empty, the result is the singleton list [""] .
The function's result 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 ( concat (make 1
sep)
(split_on_char sep s) = s ).
-No string in the result contains the sep character.
Since 4.05
Transforming
val map : f:(char -> char) -> string -> string
map f s is the string resulting from applying f to all the characters of s in increasing order.
Since 4.00
val mapi : f:(int -> char -> char) -> string -> string
mapi ~f s is like StringLabels.map but the index of the character is also passed to f .
Since 4.02
val fold_left : f:('acc -> char -> 'acc) -> init:'acc -> string -> 'acc
fold_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 .
Since 4.13
val fold_right : f:(char -> 'acc -> 'acc) -> string -> init:'acc -> 'acc
fold_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 .
Since 4.13
val for_all : f:(char -> bool) -> string -> bool
for_all p s checks if all characters in s satisfy the predicate p .
Since 4.13
val exists : f:(char -> bool) -> string -> bool
exists p s checks if at least one character of s satisfies the predicate p .
Since 4.13
val trim : string -> string
trim s is s without leading and trailing whitespace. Whitespace characters are: ' ' , '\x0C' (form feed),
'\n' , '\r' , and '\t' .
Since 4.00
val escaped : string -> string
escaped 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).
Raises Invalid_argument if the result is longer than Sys.max_string_length bytes.
val uppercase_ascii : string -> string
uppercase_ascii s is s with all lowercase letters translated to uppercase, using the US-ASCII character
set.
Since 4.05
val lowercase_ascii : string -> string
lowercase_ascii s is s with all uppercase letters translated to lowercase, using the US-ASCII character
set.
Since 4.05
val capitalize_ascii : string -> string
capitalize_ascii s is s with the first character set to uppercase, using the US-ASCII character set.
Since 4.05
val uncapitalize_ascii : string -> string
uncapitalize_ascii s is s with the first character set to lowercase, using the US-ASCII character set.
Since 4.05
Traversing
val iter : f:(char -> unit) -> string -> unit
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.[length s - 1]; () .
val iteri : f:(int -> char -> unit) -> string -> unit
iteri is like StringLabels.iter , but the function is also given the corresponding character index.
Since 4.00
Searching
val index_from : string -> int -> char -> int
index_from s i c is the index of the first occurrence of c in s after position i .
Raises Not_found if c does not occur in s after position i .
Raises Invalid_argument if i is not a valid position in s .
val index_from_opt : string -> int -> char -> int option
index_from_opt s i c is the index of the first occurrence of c in s after position i (if any).
Since 4.05
Raises Invalid_argument if i is not a valid position in s .
val rindex_from : string -> int -> char -> int
rindex_from s i c is the index of the last occurrence of c in s before position i+1 .
Raises Not_found if c does not occur in s before position i+1 .
Raises Invalid_argument if i+1 is not a valid position in s .
val rindex_from_opt : string -> int -> char -> int option
rindex_from_opt s i c is the index of the last occurrence of c in s before position i+1 (if any).
Since 4.05
Raises Invalid_argument if i+1 is not a valid position in s .
val index : string -> char -> int
index s c is String.index_from s 0 c .
val index_opt : string -> char -> int option
index_opt s c is String.index_from_opt s 0 c .
Since 4.05
val rindex : string -> char -> int
rindex s c is String.rindex_from s (length s - 1) c .
val rindex_opt : string -> char -> int option
rindex_opt s c is String.rindex_from_opt s (length s - 1) c .
Since 4.05
Strings and Sequences
val to_seq : t -> char Seq.t
to_seq s is a sequence made of the string's characters in increasing order.
Since 4.07
val to_seqi : t -> (int * char) Seq.t
to_seqi s is like StringLabels.to_seq but also tuples the corresponding index.
Since 4.07
val of_seq : char Seq.t -> t
of_seq s is a string made of the sequence's characters.
Since 4.07
UTF decoding and validations
UTF-8
val get_utf_8_uchar : t -> int -> Uchar.utf_decode
get_utf_8_uchar b i decodes an UTF-8 character at index i in b .
val is_valid_utf_8 : t -> bool
is_valid_utf_8 b is true if and only if b contains valid UTF-8 data.
UTF-16BE
val get_utf_16be_uchar : t -> int -> Uchar.utf_decode
get_utf_16be_uchar b i decodes an UTF-16BE character at index i in b .
val is_valid_utf_16be : t -> bool
is_valid_utf_16be b is true if and only if b contains valid UTF-16BE data.
UTF-16LE
val get_utf_16le_uchar : t -> int -> Uchar.utf_decode
get_utf_16le_uchar b i decodes an UTF-16LE character at index i in b .
val is_valid_utf_16le : t -> bool
is_valid_utf_16le b is true if and only if b contains valid UTF-16LE data.
Binary decoding of integers
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 -> int
get_uint8 b i is b 's unsigned 8-bit integer starting at character index i .
Since 4.13
val get_int8 : string -> int -> int
get_int8 b i is b 's signed 8-bit integer starting at character index i .
Since 4.13
val get_uint16_ne : string -> int -> int
get_uint16_ne b i is b 's native-endian unsigned 16-bit integer starting at character index i .
Since 4.13
val get_uint16_be : string -> int -> int
get_uint16_be b i is b 's big-endian unsigned 16-bit integer starting at character index i .
Since 4.13
val get_uint16_le : string -> int -> int
get_uint16_le b i is b 's little-endian unsigned 16-bit integer starting at character index i .
Since 4.13
val get_int16_ne : string -> int -> int
get_int16_ne b i is b 's native-endian signed 16-bit integer starting at character index i .
Since 4.13
val get_int16_be : string -> int -> int
get_int16_be b i is b 's big-endian signed 16-bit integer starting at character index i .
Since 4.13
val get_int16_le : string -> int -> int
get_int16_le b i is b 's little-endian signed 16-bit integer starting at character index i .
Since 4.13
val get_int32_ne : string -> int -> int32
get_int32_ne b i is b 's native-endian 32-bit integer starting at character index i .
Since 4.13
val hash : t -> int
An 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 .
Since 5.0
val seeded_hash : int -> t -> int
A 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 .
Since 5.0
val get_int32_be : string -> int -> int32
get_int32_be b i is b 's big-endian 32-bit integer starting at character index i .
Since 4.13
val get_int32_le : string -> int -> int32
get_int32_le b i is b 's little-endian 32-bit integer starting at character index i .
Since 4.13
val get_int64_ne : string -> int -> int64
get_int64_ne b i is b 's native-endian 64-bit integer starting at character index i .
Since 4.13
val get_int64_be : string -> int -> int64
get_int64_be b i is b 's big-endian 64-bit integer starting at character index i .
Since 4.13
val get_int64_le : string -> int -> int64
get_int64_le b i is b 's little-endian 64-bit integer starting at character index i .
Since 4.13