Provided by: ocaml-man_4.14.1-1ubuntu1_all 
NAME
String - Strings.
Module
Module String
Documentation
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 | +---+---+---+---+ +-----+
-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. OCaml strings used to be modifiable in place, for instance via the
String.set and String.blit functions. This use is nowadays only possible when the compiler
is put in "unsafe-string" mode by giving the -unsafe-string command-line option. This
compatibility mode makes the types string and bytes (see Bytes.t ) interchangeable so that
functions expecting byte sequences can also accept strings as arguments and modify them.
The distinction between bytes and string was introduced in OCaml 4.02, and the
"unsafe-string" compatibility mode was the default until OCaml 4.05. Starting with 4.06,
the compatibility mode is opt-in; we intend to remove the option in the future.
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 -> (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 4.02.0
Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
val empty : string
The empty string.
Since 4.13.0
val of_bytes : bytes -> string
Return a new string that contains the same bytes as the given byte sequence.
Since 4.13.0
val to_bytes : string -> bytes
Return a new byte sequence that contains the same bytes as the given string.
Since 4.13.0
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 .
Concatenating
Note. The (^) binary operator concatenates two strings.
val concat : 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 4.13.0
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 4.03.0 (4.05.0 in StringLabels)
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 4.13.0
val ends_with : suffix:string -> string -> bool
ends_with ~suffix s is true if and only if s ends with suffix .
Since 4.13.0
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 -> int -> 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 : 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 .
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 4.04.0 (4.05.0 in StringLabels)
Transforming
val map : (char -> char) -> string -> string
map f s is the string resulting from applying f to all the characters of s in increasing
order.
Since 4.00.0
val mapi : (int -> char -> char) -> string -> string
mapi f s is like String.map but the index of the character is also passed to f .
Since 4.02.0
val fold_left : ('a -> char -> 'a) -> 'a -> string -> 'a
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 4.13.0
val fold_right : (char -> 'a -> 'a) -> string -> 'a -> 'a
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 4.13.0
val for_all : (char -> bool) -> string -> bool
for_all p s checks if all characters in s satisfy the predicate p .
Since 4.13.0
val exists : (char -> bool) -> string -> bool
exists p s checks if at least one character of s satisfies the predicate p .
Since 4.13.0
val trim : string -> string
trim s is s without leading and trailing whitespace. Whitespace characters are: ' ' ,
'\x0C' (form feed), '\n' , '\r' , and '\t' .
Since 4.00.0
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 4.03.0 (4.05.0 in StringLabels)
val lowercase_ascii : string -> string
lowercase_ascii s is s with all uppercase letters translated to lowercase, using the
US-ASCII character set.
Since 4.03.0 (4.05.0 in StringLabels)
val capitalize_ascii : string -> string
capitalize_ascii s is s with the first character set to uppercase, using the US-ASCII
character set.
Since 4.03.0 (4.05.0 in StringLabels)
val uncapitalize_ascii : string -> string
uncapitalize_ascii s is s with the first character set to lowercase, using the US-ASCII
character set.
Since 4.03.0 (4.05.0 in StringLabels)
Traversing
val iter : (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 : (int -> char -> unit) -> string -> unit
iteri is like String.iter , but the function is also given the corresponding character
index.
Since 4.00.0
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. In
"unsafe-string" mode, modifications of the string during iteration will be reflected in
the sequence.
Since 4.07
val to_seqi : t -> (int * char) Seq.t
to_seqi s is like String.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.
Deprecated functions
val create : int -> bytes
Deprecated. This is a deprecated alias of Bytes.create / BytesLabels.create .
create n returns a fresh byte sequence of length n . The sequence is uninitialized and
contains arbitrary bytes.
Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
val set : bytes -> int -> char -> unit
Deprecated. This is a deprecated alias of Bytes.set / BytesLabels.set .
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 set s n c .
Raises Invalid_argument if n is not a valid index in s .
val blit : string -> int -> bytes -> int -> int -> unit
blit src src_pos dst dst_pos len copies len bytes from the string src , starting at index
src_pos , to byte sequence dst , starting at character number dst_pos .
Raises Invalid_argument if src_pos and len do not designate a valid range of src , or if
dst_pos and len do not designate a valid range of dst .
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 fill : bytes -> int -> int -> char -> unit
Deprecated. This is a deprecated alias of Bytes.fill / BytesLabels.fill .
fill s pos len c modifies byte sequence s in place, replacing len bytes by c , starting at
pos .
Raises Invalid_argument if pos and len do not designate a valid substring of s .
val uppercase : string -> string
Deprecated. Functions operating on Latin-1 character set are deprecated.
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
Deprecated. Functions operating on Latin-1 character set are deprecated.
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
Deprecated. Functions operating on Latin-1 character set are deprecated.
Return a copy of the argument, with the first character set to uppercase, using the ISO
Latin-1 (8859-1) character set..
val uncapitalize : string -> string
Deprecated. Functions operating on Latin-1 character set are deprecated.
Return a copy of the argument, with the first character set to lowercase, using the ISO
Latin-1 (8859-1) character set.
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 4.13.0
val get_int8 : string -> int -> int
get_int8 b i is b 's signed 8-bit integer starting at character index i .
Since 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0
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 4.13.0