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. 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.
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 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.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 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 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 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 iterator.
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 create : int -> bytescreate n returns a fresh byte sequence of length n.
The sequence is uninitialized and contains arbitrary bytes.
Invalid_argument if n < 0 or n > Sys.max_string_length.val set : bytes -> int -> char -> unitset 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.
Invalid_argument if n is not a valid index in s.val blit : string -> int -> bytes -> int -> int -> unitblit 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.
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 -> stringReturn a copy of the given string.
val fill : bytes -> int -> int -> char -> unitfill s pos len c modifies byte sequence s in place,
replacing len bytes by c, starting at pos.
Invalid_argument if pos and len do not
designate a valid substring of s.val uppercase : string -> stringReturn 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 -> stringReturn 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 -> stringReturn a copy of the argument, with the first character set to uppercase, using the ISO Latin-1 (8859-1) character set..
val uncapitalize : string -> stringReturn a copy of the argument, with the first character set to lowercase, using the ISO Latin-1 (8859-1) character set.