1StringLabels(3) OCaml library StringLabels(3)
2
6 StringLabels - Strings.
7
9 Module StringLabels
10
12 Module StringLabels
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 -> f:(int -> char) -> string
82 init n ~f is a string of length n with index i holding the character f
85 i (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 : sep:string -> string list -> string
147 concat ~sep ss concatenates the list of strings ss , inserting the sep‐
150 arator 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 4.05.0
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 -> pos:int -> len:int -> string
245 sub s ~pos ~len is a string of length len , containing the substring of
248 s 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 : sep:char -> string -> string list
257 split_on_char ~sep s is the list of all (possibly empty) substrings of
260 s 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 4.05.0
275 Transforming
280 val map : f:(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 : f:(int -> char -> char) -> string -> string
292 mapi ~f s is like StringLabels.map but the index of the character is
295 also passed to f .
296 Since 4.02.0
299 val fold_left : f:('a -> char -> 'a) -> init:'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 : f:(char -> 'a -> 'a) -> string -> init:'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 : f:(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 : f:(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 4.05.0
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 4.05.0
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 4.05.0
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 4.05.0
416 Traversing
421 val iter : f:(char -> unit) -> string -> unit
422 iter ~f s applies function f in turn to all the characters of s . It
425 is equivalent to f s.[0]; f s.[1]; ...; f s.[length s - 1]; () .
426 val iteri : f:(int -> char -> unit) -> string -> unit
430 iteri is like StringLabels.iter , but the function is also given the
433 corresponding 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 StringLabels.to_seq but also tuples the corresponding
550 index.
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 : src:string -> src_pos:int -> dst:bytes -> dst_pos:int ->
619 len:int -> unit
620 blit ~src ~src_pos ~dst ~dst_pos ~len copies len bytes from the string
623 src , starting at index src_pos , to byte sequence dst , starting at
624 character number dst_pos .
625 Raises Invalid_argument if src_pos and len do not designate a valid
628 range of src , or if dst_pos and len do not designate a valid range of
629 dst .
630 Binary decoding of integers
635 The functions in this section binary decode integers from strings.
636 All following functions raise Invalid_argument if the characters needed
638 at index i to decode the integer are not available.
639 Little-endian (resp. big-endian) encoding means that least (resp. most)
641 significant bytes are stored first. Big-endian is also known as net‐
642 work byte order. Native-endian encoding is either little-endian or
643 big-endian depending on Sys.big_endian .
644 32-bit and 64-bit integers are represented by the int32 and int64
646 types, which can be interpreted either as signed or unsigned numbers.
647 8-bit and 16-bit integers are represented by the int type, which has
649 more bits than the binary encoding. These extra bits are sign-extended
650 (or zero-extended) for functions which decode 8-bit or 16-bit integers
651 and represented them with int values.
652 val get_uint8 : string -> int -> int
654 get_uint8 b i is b 's unsigned 8-bit integer starting at character in‐
657 dex i .
658 Since 4.13.0
661 val get_int8 : string -> int -> int
665 get_int8 b i is b 's signed 8-bit integer starting at character index i
668 .
669 Since 4.13.0
672 val get_uint16_ne : string -> int -> int
676 get_uint16_ne b i is b 's native-endian unsigned 16-bit integer start‐
679 ing at character index i .
680 Since 4.13.0
683 val get_uint16_be : string -> int -> int
687 get_uint16_be b i is b 's big-endian unsigned 16-bit integer starting
690 at character index i .
691 Since 4.13.0
694 val get_uint16_le : string -> int -> int
698 get_uint16_le b i is b 's little-endian unsigned 16-bit integer start‐
701 ing at character index i .
702 Since 4.13.0
705 val get_int16_ne : string -> int -> int
709 get_int16_ne b i is b 's native-endian signed 16-bit integer starting
712 at character index i .
713 Since 4.13.0
716 val get_int16_be : string -> int -> int
720 get_int16_be b i is b 's big-endian signed 16-bit integer starting at
723 character index i .
724 Since 4.13.0
727 val get_int16_le : string -> int -> int
731 get_int16_le b i is b 's little-endian signed 16-bit integer starting
734 at character index i .
735 Since 4.13.0
738 val get_int32_ne : string -> int -> int32
742 get_int32_ne b i is b 's native-endian 32-bit integer starting at char‐
745 acter index i .
746 Since 4.13.0
749 val hash : t -> int
753 An unseeded hash function for strings, with the same output value as
755 Hashtbl.hash . This function allows this module to be passed as argu‐
756 ment to the functor Hashtbl.Make .
757 Since 5.0.0
760 val seeded_hash : int -> t -> int
764 A seeded hash function for strings, with the same output value as
766 Hashtbl.seeded_hash . This function allows this module to be passed as
767 argument to the functor Hashtbl.MakeSeeded .
768 Since 5.0.0
771 val get_int32_be : string -> int -> int32
775 get_int32_be b i is b 's big-endian 32-bit integer starting at charac‐
778 ter index i .
779 Since 4.13.0
782 val get_int32_le : string -> int -> int32
786 get_int32_le b i is b 's little-endian 32-bit integer starting at char‐
789 acter index i .
790 Since 4.13.0
793 val get_int64_ne : string -> int -> int64
797 get_int64_ne b i is b 's native-endian 64-bit integer starting at char‐
800 acter index i .
801 Since 4.13.0
804 val get_int64_be : string -> int -> int64
808 get_int64_be b i is b 's big-endian 64-bit integer starting at charac‐
811 ter index i .
812 Since 4.13.0
815 val get_int64_le : string -> int -> int64
819 get_int64_le b i is b 's little-endian 64-bit integer starting at char‐
822 acter index i .
823 Since 4.13.0
826OCamldoc 2023-07-20 StringLabels(3)