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. 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.
make n c is a string of length n with each index holding the character c.
init n f is a string of length n with index i holding the character f i (called in increasing index order).
get s i is the character at index i in s. This is the same as writing s.[i].
Return a new string that contains the same bytes as the given byte sequence.
Return a new byte sequence that contains the same bytes as the given string.
Same as Bytes.blit_string which should be preferred.
Note. The Stdlib.(^) binary operator concatenates two strings.
concat sep ss concatenates the list of strings ss, inserting the separator string sep between each.
compare s0 s1 sorts s0 and s1 in lexicographical order. compare behaves like Stdlib.compare on strings but may be more efficient.
starts_with ~prefix s is true if and only if s starts with prefix.
ends_with ~suffix s is true if and only if s ends with suffix.
contains_from s start c is true if and only if c appears in s after position start.
rcontains_from s stop c is true if and only if c appears in s before position stop+1.
contains s c is String.contains_from s 0 c.
sub s pos len is a string of length len, containing the substring of s that starts at position pos and has length len.
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:
sep as a separator returns a string equal to the input (concat (make 1 sep)
(split_on_char sep s) = s).sep character.map f s is the string resulting from applying f to all the characters of s in increasing order.
mapi f s is like map but the index of the character is also passed to f.
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.
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.
for_all p s checks if all characters in s satisfy the predicate p.
exists p s checks if at least one character of s satisfies the predicate p.
trim s is s without leading and trailing whitespace. Whitespace characters are: ' ', '\x0C' (form feed), '\n', '\r', and '\t'.
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).
uppercase_ascii s is s with all lowercase letters translated to uppercase, using the US-ASCII character set.
lowercase_ascii s is s with all uppercase letters translated to lowercase, using the US-ASCII character set.
capitalize_ascii s is s with the first character set to uppercase, using the US-ASCII character set.
uncapitalize_ascii s is s with the first character set to lowercase, using the US-ASCII character set.
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]; ().
iteri is like iter, but the function is also given the corresponding character index.
index_from s i c is the index of the first occurrence of c in s after position i.
index_from_opt s i c is the index of the first occurrence of c in s after position i (if any).
rindex_from s i c is the index of the last occurrence of c in s before position i+1.
rindex_from_opt s i c is the index of the last occurrence of c in s before position i+1 (if any).
index s c is String.index_from s 0 c.
index_opt s c is String.index_from_opt s 0 c.
rindex s c is String.rindex_from s (length s - 1) c.
rindex_opt s c is String.rindex_from_opt s (length s - 1) c.
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.
to_seqi s is like to_seq but also tuples the corresponding index.
val get_utf_8_uchar : t -> int -> Uchar.utf_decodeget_utf_8_uchar b i decodes an UTF-8 character at index i in b.
val is_valid_utf_8 : t -> boolis_valid_utf_8 b is true if and only if b contains valid UTF-8 data.
val get_utf_16be_uchar : t -> int -> Uchar.utf_decodeget_utf_16be_uchar b i decodes an UTF-16BE character at index i in b.
val is_valid_utf_16be : t -> boolis_valid_utf_16be b is true if and only if b contains valid UTF-16BE data.
val get_utf_16le_uchar : t -> int -> Uchar.utf_decodeget_utf_16le_uchar b i decodes an UTF-16LE character at index i in b.
val is_valid_utf_16le : t -> boolis_valid_utf_16le b is true if and only if b contains valid UTF-16LE data.
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.
get_uint8 b i is b's unsigned 8-bit integer starting at character index i.
get_int8 b i is b's signed 8-bit integer starting at character index i.
get_uint16_ne b i is b's native-endian unsigned 16-bit integer starting at character index i.
get_uint16_be b i is b's big-endian unsigned 16-bit integer starting at character index i.
get_uint16_le b i is b's little-endian unsigned 16-bit integer starting at character index i.
get_int16_ne b i is b's native-endian signed 16-bit integer starting at character index i.
get_int16_be b i is b's big-endian signed 16-bit integer starting at character index i.
get_int16_le b i is b's little-endian signed 16-bit integer starting at character index i.
get_int32_ne b i is b's native-endian 32-bit integer starting at character index i.
get_int32_be b i is b's big-endian 32-bit integer starting at character index i.
get_int32_le b i is b's little-endian 32-bit integer starting at character index i.
get_int64_ne b i is b's native-endian 64-bit integer starting at character index i.
get_int64_be b i is b's big-endian 64-bit integer starting at character index i.
get_int64_le b i is b's little-endian 64-bit integer starting at character index i.
val hash : t -> intAn 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.
val seeded_hash : int -> t -> intA seeded hash function for strings, with the same output value as Hashtbl.seeded_hash. This function allows this module to be passed as argument to the functor Hashtbl.MakeSeeded.