1String(3) OCaml library String(3)
2
6 String - Strings.
7
9 Module String
10
12 Module String
13 : sig end
14 Strings.
17 A string s of length n is an indexable and immutable sequence of n
19 bytes. For historical reasons these bytes are referred to as charac‐
20 ters.
21 The semantics of string functions is defined in terms of indices and
23 positions. These are depicted and described as follows.
24 positions 0 1 2 3 4 n-1 n +---+---+---+---+ +-----+
26 indices | 0 | 1 | 2 | 3 | ... | n-1 | +---+---+---+---+ +-----+
27 -An index i of s is an integer in the range [ 0 ; n-1 ]. It represents
29 the i th byte (character) of s which can be accessed using the constant
30 time string indexing operator s.[i] .
31 -A position i of s is an integer in the range [ 0 ; n ]. It represents
33 either the point at the beginning of the string, or the point between
34 two indices, or the point at the end of the string. The i th byte index
35 is between position i and i+1 .
36 Two integers start and len are said to define a valid substring of s if
39 len >= 0 and start , start+len are positions of s .
40 Unicode text. Strings being arbitrary sequences of bytes, they can hold
42 any kind of textual encoding. However the recommended encoding for
43 storing Unicode text in OCaml strings is UTF-8. This is the encoding
44 used by Unicode escapes in string literals. For example the string
45 "\u{1F42B}" is the UTF-8 encoding of the Unicode character U+1F42B.
46 Past mutability. Before OCaml 4.02, strings used to be modifiable in
48 place like Bytes.t mutable sequences of bytes. OCaml 4 had various
49 compiler flags and configuration options to support the transition pe‐
50 riod from mutable to immutable strings. Those options are no longer
51 available, and strings are now always immutable.
52 The labeled version of this module can be used as described in the Std‐
54 Labels module.
55 Strings
63 type t = string
64 The type for strings.
67 val make : int -> char -> string
71 make n c is a string of length n with each index holding the character
74 c .
75 Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
78 val init : int -> (int -> char) -> string
82 init n f is a string of length n with index i holding the character f i
85 (called in increasing index order).
86 Since 4.02.0
89 Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
92 val empty : string
96 The empty string.
98 Since 4.13.0
101 val of_bytes : bytes -> string
105 Return a new string that contains the same bytes as the given byte se‐
107 quence.
108 Since 4.13.0
111 val to_bytes : string -> bytes
115 Return a new byte sequence that contains the same bytes as the given
117 string.
118 Since 4.13.0
121 val length : string -> int
125 length s is the length (number of bytes/characters) of s .
128 val get : string -> int -> char
132 get s i is the character at index i in s . This is the same as writing
135 s.[i] .
136 Raises Invalid_argument if i not an index of s .
139 Concatenating
144 Note. The (^) binary operator concatenates two strings.
145 val concat : string -> string list -> string
147 concat sep ss concatenates the list of strings ss , inserting the sepa‐
150 rator string sep between each.
151 Raises Invalid_argument if the result is longer than
154 Sys.max_string_length bytes.
155 val cat : string -> string -> string
159 cat s1 s2 concatenates s1 and s2 ( s1 ^ s2 ).
162 Since 4.13.0
165 Raises Invalid_argument if the result is longer than
168 Sys.max_string_length bytes.
169 Predicates and comparisons
174 val equal : t -> t -> bool
175 equal s0 s1 is true if and only if s0 and s1 are character-wise equal.
178 Since 4.03.0 (4.05.0 in StringLabels)
181 val compare : t -> t -> int
185 compare s0 s1 sorts s0 and s1 in lexicographical order. compare be‐
188 haves like compare on strings but may be more efficient.
189 val starts_with : prefix:string -> string -> bool
193 starts_with ~prefix s is true if and only if s starts with prefix .
196 Since 4.13.0
199 val ends_with : suffix:string -> string -> bool
203 ends_with ~suffix s is true if and only if s ends with suffix .
206 Since 4.13.0
209 val contains_from : string -> int -> char -> bool
213 contains_from s start c is true if and only if c appears in s after po‐
216 sition start .
217 Raises Invalid_argument if start is not a valid position in s .
220 val rcontains_from : string -> int -> char -> bool
224 rcontains_from s stop c is true if and only if c appears in s before
227 position stop+1 .
228 Raises Invalid_argument if stop < 0 or stop+1 is not a valid position
231 in s .
232 val contains : string -> char -> bool
236 contains s c is String.contains_from s 0 c .
239 Extracting substrings
244 val sub : string -> int -> int -> string
245 sub s pos len is a string of length len , containing the substring of s
248 that starts at position pos and has length len .
249 Raises Invalid_argument if pos and len do not designate a valid sub‐
252 string of s .
253 val split_on_char : char -> string -> string list
257 split_on_char sep s is the list of all (possibly empty) substrings of s
260 that are delimited by the character sep .
261 The function's result is specified by the following invariants:
263 -The list is not empty.
265 -Concatenating its elements using sep as a separator returns a string
267 equal to the input ( concat (make 1 sep)
268 (split_on_char sep s) = s ).
269 -No string in the result contains the sep character.
271 Since 4.04.0 (4.05.0 in StringLabels)
275 Transforming
280 val map : (char -> char) -> string -> string
281 map f s is the string resulting from applying f to all the characters
284 of s in increasing order.
285 Since 4.00.0
288 val mapi : (int -> char -> char) -> string -> string
292 mapi f s is like String.map but the index of the character is also
295 passed to f .
296 Since 4.02.0
299 val fold_left : ('a -> char -> 'a) -> 'a -> string -> 'a
303 fold_left f x s computes f (... (f (f x s.[0]) s.[1]) ...) s.[n-1] ,
306 where n is the length of the string s .
307 Since 4.13.0
310 val fold_right : (char -> 'a -> 'a) -> string -> 'a -> 'a
314 fold_right f s x computes f s.[0] (f s.[1] ( ... (f s.[n-1] x) ...)) ,
317 where n is the length of the string s .
318 Since 4.13.0
321 val for_all : (char -> bool) -> string -> bool
325 for_all p s checks if all characters in s satisfy the predicate p .
328 Since 4.13.0
331 val exists : (char -> bool) -> string -> bool
335 exists p s checks if at least one character of s satisfies the predi‐
338 cate p .
339 Since 4.13.0
342 val trim : string -> string
346 trim s is s without leading and trailing whitespace. Whitespace charac‐
349 ters are: ' ' , '\x0C' (form feed), '\n' , '\r' , and '\t' .
350 Since 4.00.0
353 val escaped : string -> string
357 escaped s is s with special characters represented by escape sequences,
360 following the lexical conventions of OCaml.
361 All characters outside the US-ASCII printable range [0x20;0x7E] are es‐
363 caped, as well as backslash (0x2F) and double-quote (0x22).
364 The function Scanf.unescaped is a left inverse of escaped , i.e.
366 Scanf.unescaped (escaped s) = s for any string s (unless escaped s
367 fails).
368 Raises Invalid_argument if the result is longer than
371 Sys.max_string_length bytes.
372 val uppercase_ascii : string -> string
376 uppercase_ascii s is s with all lowercase letters translated to upper‐
379 case, using the US-ASCII character set.
380 Since 4.03.0 (4.05.0 in StringLabels)
383 val lowercase_ascii : string -> string
387 lowercase_ascii s is s with all uppercase letters translated to lower‐
390 case, using the US-ASCII character set.
391 Since 4.03.0 (4.05.0 in StringLabels)
394 val capitalize_ascii : string -> string
398 capitalize_ascii s is s with the first character set to uppercase, us‐
401 ing the US-ASCII character set.
402 Since 4.03.0 (4.05.0 in StringLabels)
405 val uncapitalize_ascii : string -> string
409 uncapitalize_ascii s is s with the first character set to lowercase,
412 using the US-ASCII character set.
413 Since 4.03.0 (4.05.0 in StringLabels)
416 Traversing
421 val iter : (char -> unit) -> string -> unit
422 iter f s applies function f in turn to all the characters of s . It is
425 equivalent to f s.[0]; f s.[1]; ...; f s.[length s - 1]; () .
426 val iteri : (int -> char -> unit) -> string -> unit
430 iteri is like String.iter , but the function is also given the corre‐
433 sponding character index.
434 Since 4.00.0
437 Searching
442 val index_from : string -> int -> char -> int
443 index_from s i c is the index of the first occurrence of c in s after
446 position i .
447 Raises Not_found if c does not occur in s after position i .
450 Raises Invalid_argument if i is not a valid position in s .
453 val index_from_opt : string -> int -> char -> int option
457 index_from_opt s i c is the index of the first occurrence of c in s af‐
460 ter position i (if any).
461 Since 4.05
464 Raises Invalid_argument if i is not a valid position in s .
467 val rindex_from : string -> int -> char -> int
471 rindex_from s i c is the index of the last occurrence of c in s before
474 position i+1 .
475 Raises Not_found if c does not occur in s before position i+1 .
478 Raises Invalid_argument if i+1 is not a valid position in s .
481 val rindex_from_opt : string -> int -> char -> int option
485 rindex_from_opt s i c is the index of the last occurrence of c in s be‐
488 fore position i+1 (if any).
489 Since 4.05
492 Raises Invalid_argument if i+1 is not a valid position in s .
495 val index : string -> char -> int
499 index s c is String.index_from s 0 c .
502 val index_opt : string -> char -> int option
506 index_opt s c is String.index_from_opt s 0 c .
509 Since 4.05
512 val rindex : string -> char -> int
516 rindex s c is String.rindex_from s (length s - 1) c .
519 val rindex_opt : string -> char -> int option
523 rindex_opt s c is String.rindex_from_opt s (length s - 1) c .
526 Since 4.05
529 Strings and Sequences
534 val to_seq : t -> char Seq.t
535 to_seq s is a sequence made of the string's characters in increasing
538 order. In "unsafe-string" mode, modifications of the string during it‐
539 eration will be reflected in the sequence.
540 Since 4.07
543 val to_seqi : t -> (int * char) Seq.t
547 to_seqi s is like String.to_seq but also tuples the corresponding in‐
550 dex.
551 Since 4.07
554 val of_seq : char Seq.t -> t
558 of_seq s is a string made of the sequence's characters.
561 Since 4.07
564 UTF decoding and validations
569 UTF-8
570 val get_utf_8_uchar : t -> int -> Uchar.utf_decode
571 get_utf_8_uchar b i decodes an UTF-8 character at index i in b .
574 val is_valid_utf_8 : t -> bool
578 is_valid_utf_8 b is true if and only if b contains valid UTF-8 data.
581 UTF-16BE
586 val get_utf_16be_uchar : t -> int -> Uchar.utf_decode
587 get_utf_16be_uchar b i decodes an UTF-16BE character at index i in b .
590 val is_valid_utf_16be : t -> bool
594 is_valid_utf_16be b is true if and only if b contains valid UTF-16BE
597 data.
598 UTF-16LE
603 val get_utf_16le_uchar : t -> int -> Uchar.utf_decode
604 get_utf_16le_uchar b i decodes an UTF-16LE character at index i in b .
607 val is_valid_utf_16le : t -> bool
611 is_valid_utf_16le b is true if and only if b contains valid UTF-16LE
614 data.
615 val blit : string -> int -> bytes -> int -> int -> unit
619 blit src src_pos dst dst_pos len copies len bytes from the string src ,
622 starting at index src_pos , to byte sequence dst , starting at charac‐
623 ter number dst_pos .
624 Raises Invalid_argument if src_pos and len do not designate a valid
627 range of src , or if dst_pos and len do not designate a valid range of
628 dst .
629 Binary decoding of integers
634 The functions in this section binary decode integers from strings.
635 All following functions raise Invalid_argument if the characters needed
637 at index i to decode the integer are not available.
638 Little-endian (resp. big-endian) encoding means that least (resp. most)
640 significant bytes are stored first. Big-endian is also known as net‐
641 work byte order. Native-endian encoding is either little-endian or
642 big-endian depending on Sys.big_endian .
643 32-bit and 64-bit integers are represented by the int32 and int64
645 types, which can be interpreted either as signed or unsigned numbers.
646 8-bit and 16-bit integers are represented by the int type, which has
648 more bits than the binary encoding. These extra bits are sign-extended
649 (or zero-extended) for functions which decode 8-bit or 16-bit integers
650 and represented them with int values.
651 val get_uint8 : string -> int -> int
653 get_uint8 b i is b 's unsigned 8-bit integer starting at character in‐
656 dex i .
657 Since 4.13.0
660 val get_int8 : string -> int -> int
664 get_int8 b i is b 's signed 8-bit integer starting at character index i
667 .
668 Since 4.13.0
671 val get_uint16_ne : string -> int -> int
675 get_uint16_ne b i is b 's native-endian unsigned 16-bit integer start‐
678 ing at character index i .
679 Since 4.13.0
682 val get_uint16_be : string -> int -> int
686 get_uint16_be b i is b 's big-endian unsigned 16-bit integer starting
689 at character index i .
690 Since 4.13.0
693 val get_uint16_le : string -> int -> int
697 get_uint16_le b i is b 's little-endian unsigned 16-bit integer start‐
700 ing at character index i .
701 Since 4.13.0
704 val get_int16_ne : string -> int -> int
708 get_int16_ne b i is b 's native-endian signed 16-bit integer starting
711 at character index i .
712 Since 4.13.0
715 val get_int16_be : string -> int -> int
719 get_int16_be b i is b 's big-endian signed 16-bit integer starting at
722 character index i .
723 Since 4.13.0
726 val get_int16_le : string -> int -> int
730 get_int16_le b i is b 's little-endian signed 16-bit integer starting
733 at character index i .
734 Since 4.13.0
737 val get_int32_ne : string -> int -> int32
741 get_int32_ne b i is b 's native-endian 32-bit integer starting at char‐
744 acter index i .
745 Since 4.13.0
748 val hash : t -> int
752 An unseeded hash function for strings, with the same output value as
754 Hashtbl.hash . This function allows this module to be passed as argu‐
755 ment to the functor Hashtbl.Make .
756 Since 5.0.0
759 val seeded_hash : int -> t -> int
763 A seeded hash function for strings, with the same output value as
765 Hashtbl.seeded_hash . This function allows this module to be passed as
766 argument to the functor Hashtbl.MakeSeeded .
767 Since 5.0.0
770 val get_int32_be : string -> int -> int32
774 get_int32_be b i is b 's big-endian 32-bit integer starting at charac‐
777 ter index i .
778 Since 4.13.0
781 val get_int32_le : string -> int -> int32
785 get_int32_le b i is b 's little-endian 32-bit integer starting at char‐
788 acter index i .
789 Since 4.13.0
792 val get_int64_ne : string -> int -> int64
796 get_int64_ne b i is b 's native-endian 64-bit integer starting at char‐
799 acter index i .
800 Since 4.13.0
803 val get_int64_be : string -> int -> int64
807 get_int64_be b i is b 's big-endian 64-bit integer starting at charac‐
810 ter index i .
811 Since 4.13.0
814 val get_int64_le : string -> int -> int64
818 get_int64_le b i is b 's little-endian 64-bit integer starting at char‐
821 acter index i .
822 Since 4.13.0
825OCamldoc 2023-07-20 String(3)