Module Stdlib.StringSource
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 ith 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 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. 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
Sourceval make : int -> char -> string make n c is a string of length n with each index holding the character c.
Sourceval 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).
Sourceval length : string -> int length s is the length (number of bytes/characters) of s.
Sourceval get : string -> int -> char get s i is the character at index i in s. This is the same as writing s.[i].
Sourceval of_bytes : bytes -> string Return a new string that contains the same bytes as the given byte sequence.
Sourceval to_bytes : string -> bytes Return a new byte sequence that contains the same bytes as the given string.
Sourceval blit : string -> int -> bytes -> int -> int -> unit Concatenating
Note. The Stdlib.(^) binary operator concatenates two strings.
Sourceval concat : string -> string list -> string concat sep ss concatenates the list of strings ss, inserting the separator string sep between each.
Sourceval cat : string -> string -> string cat s1 s2 concatenates s1 and s2 (s1 ^ s2).
Predicates and comparisons
equal s0 s1 is true if and only if s0 and s1 are character-wise equal.
compare s0 s1 sorts s0 and s1 in lexicographical order. compare behaves like Stdlib.compare on strings but may be more efficient.
Sourceval starts_with : prefix:string -> string -> bool starts_with ~prefix s is true if and only if s starts with prefix.
Sourceval ends_with : suffix:string -> string -> bool ends_with ~suffix s is true if and only if s ends with suffix.
Sourceval contains_from : string -> int -> char -> bool contains_from s start c is true if and only if c appears in s after position start.
Sourceval 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.
Sourceval contains : string -> char -> bool Sourceval 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.
Sourceval 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. 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.
Sourceval map : (char -> char) -> string -> string map f s is the string resulting from applying f to all the characters of s in increasing order.
Sourceval mapi : (int -> char -> char) -> string -> string mapi f s is like map but the index of the character is also passed to f.
Sourceval fold_left : ('acc -> char -> 'acc) -> '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.
Sourceval fold_right : (char -> 'acc -> 'acc) -> string -> '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.
Sourceval for_all : (char -> bool) -> string -> bool for_all p s checks if all characters in s satisfy the predicate p.
Sourceval exists : (char -> bool) -> string -> bool exists p s checks if at least one character of s satisfies the predicate p.
Sourceval trim : string -> string trim s is s without leading and trailing whitespace. Whitespace characters are: ' ', '\x0C' (form feed), '\n', '\r', and '\t'.
Sourceval 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).
Sourceval uppercase_ascii : string -> string uppercase_ascii s is s with all lowercase letters translated to uppercase, using the US-ASCII character set.
Sourceval lowercase_ascii : string -> string lowercase_ascii s is s with all uppercase letters translated to lowercase, using the US-ASCII character set.
Sourceval capitalize_ascii : string -> string capitalize_ascii s is s with the first character set to uppercase, using the US-ASCII character set.
Sourceval uncapitalize_ascii : string -> string uncapitalize_ascii s is s with the first character set to lowercase, using the US-ASCII character set.
Traversing
Sourceval 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]; ().
Sourceval iteri : (int -> char -> unit) -> string -> unit iteri is like iter, but the function is also given the corresponding character index.
Searching
Sourceval 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.
Sourceval 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).
Sourceval 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.
Sourceval 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).
Sourceval index : string -> char -> int Sourceval index_opt : string -> char -> int option Sourceval rindex : string -> char -> int Sourceval rindex_opt : string -> char -> int option Strings and Sequences
to_seq s is a sequence made of the string's characters in increasing order.
to_seqi s is like to_seq but also tuples the corresponding index.
of_seq s is a string made of the sequence's characters.
UTF decoding and validations
UTF-8
get_utf_8_uchar b i decodes an UTF-8 character at index i in b.
Sourceval 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
get_utf_16be_uchar b i decodes an UTF-16BE character at index i in b.
Sourceval 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
get_utf_16le_uchar b i decodes an UTF-16LE character at index i in b.
Sourceval 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.
Sourceval get_uint8 : string -> int -> int get_uint8 b i is b's unsigned 8-bit integer starting at character index i.
Sourceval get_int8 : string -> int -> int get_int8 b i is b's signed 8-bit integer starting at character index i.
Sourceval 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.
Sourceval 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.
Sourceval 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.
Sourceval 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.
Sourceval 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.
Sourceval 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.
Sourceval get_int32_ne : string -> int -> int32 get_int32_ne b i is b's native-endian 32-bit integer starting at character index i.
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.
Sourceval seeded_hash : int -> t -> int Sourceval get_int32_be : string -> int -> int32 get_int32_be b i is b's big-endian 32-bit integer starting at character index i.
Sourceval get_int32_le : string -> int -> int32 get_int32_le b i is b's little-endian 32-bit integer starting at character index i.
Sourceval get_int64_ne : string -> int -> int64 get_int64_ne b i is b's native-endian 64-bit integer starting at character index i.
Sourceval get_int64_be : string -> int -> int64 get_int64_be b i is b's big-endian 64-bit integer starting at character index i.
Sourceval get_int64_le : string -> int -> int64 get_int64_le b i is b's little-endian 64-bit integer starting at character index i.