Module StringLabels
: sigend
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 i th 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 i th 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.
Stringstypet = string
The type for strings.
valmake : int->char->stringmakenc is a string of length n with each index holding the character c .
RaisesInvalid_argument if n<0 or n>Sys.max_string_length .
valinit : int->f:(int->char)->stringinitn~f is a string of length n with index i holding the character fi (called in increasing index
order).
Since 4.02
RaisesInvalid_argument if n<0 or n>Sys.max_string_length .
valempty : string
The empty string.
Since 4.13
vallength : string->intlengths is the length (number of bytes/characters) of s .
valget : string->int->chargetsi is the character at index i in s . This is the same as writing s.[i] .
RaisesInvalid_argument if i not an index of s .
valof_bytes : bytes->string
Return a new string that contains the same bytes as the given byte sequence.
Since 4.13
valto_bytes : string->bytes
Return a new byte sequence that contains the same bytes as the given string.
Since 4.13
valblit : src:string->src_pos:int->dst:bytes->dst_pos:int->len:int->unit
Same as Bytes.blit_string which should be preferred.
Concatenating
Note. The (^) binary operator concatenates two strings.
valconcat : sep:string->stringlist->stringconcat~sepss concatenates the list of strings ss , inserting the separator string sep between each.
RaisesInvalid_argument if the result is longer than Sys.max_string_length bytes.
valcat : string->string->stringcats1s2 concatenates s1 and s2 ( s1^s2 ).
Since 4.13
RaisesInvalid_argument if the result is longer than Sys.max_string_length bytes.
Predicatesandcomparisonsvalequal : t->t->boolequals0s1 is true if and only if s0 and s1 are character-wise equal.
Since 4.05
valcompare : t->t->intcompares0s1 sorts s0 and s1 in lexicographical order. compare behaves like compare on strings but may
be more efficient.
valstarts_with : prefix:string->string->boolstarts_with~prefixs is true if and only if s starts with prefix .
Since 4.13
valends_with : suffix:string->string->boolends_with~suffixs is true if and only if s ends with suffix .
Since 4.13
valcontains_from : string->int->char->boolcontains_fromsstartc is true if and only if c appears in s after position start .
RaisesInvalid_argument if start is not a valid position in s .
valrcontains_from : string->int->char->boolrcontains_fromsstopc is true if and only if c appears in s before position stop+1 .
RaisesInvalid_argument if stop<0 or stop+1 is not a valid position in s .
valcontains : string->char->boolcontainssc is String.contains_froms0c .
Extractingsubstringsvalsub : string->pos:int->len:int->stringsubs~pos~len is a string of length len , containing the substring of s that starts at position pos and
has length len .
RaisesInvalid_argument if pos and len do not designate a valid substring of s .
valsplit_on_char : sep:char->string->stringlistsplit_on_char~seps 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(make1sep)(split_on_charseps)=s ).
-No string in the result contains the sep character.
Since 4.05
Transformingvalmap : f:(char->char)->string->stringmapfs is the string resulting from applying f to all the characters of s in increasing order.
Since 4.00
valmapi : f:(int->char->char)->string->stringmapi~fs is like StringLabels.map but the index of the character is also passed to f .
Since 4.02
valfold_left : f:('acc->char->'acc)->init:'acc->string->'accfold_leftfxs computes f(...(f(fxs.[0])s.[1])...)s.[n-1] , where n is the length of the string
s .
Since 4.13
valfold_right : f:(char->'acc->'acc)->string->init:'acc->'accfold_rightfsx computes fs.[0](fs.[1](...(fs.[n-1]x)...)) , where n is the length of the
string s .
Since 4.13
valfor_all : f:(char->bool)->string->boolfor_allps checks if all characters in s satisfy the predicate p .
Since 4.13
valexists : f:(char->bool)->string->boolexistsps checks if at least one character of s satisfies the predicate p .
Since 4.13
valtrim : string->stringtrims is s without leading and trailing whitespace. Whitespace characters are: '' , '\x0C' (form feed),
'\n' , '\r' , and '\t' .
Since 4.00
valescaped : string->stringescapeds 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(escapeds)=s for any
string s (unless escapeds fails).
RaisesInvalid_argument if the result is longer than Sys.max_string_length bytes.
valuppercase_ascii : string->stringuppercase_asciis is s with all lowercase letters translated to uppercase, using the US-ASCII character
set.
Since 4.05
vallowercase_ascii : string->stringlowercase_asciis is s with all uppercase letters translated to lowercase, using the US-ASCII character
set.
Since 4.05
valcapitalize_ascii : string->stringcapitalize_asciis is s with the first character set to uppercase, using the US-ASCII character set.
Since 4.05
valuncapitalize_ascii : string->stringuncapitalize_asciis is s with the first character set to lowercase, using the US-ASCII character set.
Since 4.05
Traversingvaliter : f:(char->unit)->string->unititer~fs applies function f in turn to all the characters of s . It is equivalent to fs.[0];fs.[1];...;fs.[lengths-1];() .
valiteri : f:(int->char->unit)->string->unititeri is like StringLabels.iter , but the function is also given the corresponding character index.
Since 4.00
Searchingvalindex_from : string->int->char->intindex_fromsic is the index of the first occurrence of c in s after position i .
RaisesNot_found if c does not occur in s after position i .
RaisesInvalid_argument if i is not a valid position in s .
valindex_from_opt : string->int->char->intoptionindex_from_optsic is the index of the first occurrence of c in s after position i (if any).
Since 4.05
RaisesInvalid_argument if i is not a valid position in s .
valrindex_from : string->int->char->intrindex_fromsic is the index of the last occurrence of c in s before position i+1 .
RaisesNot_found if c does not occur in s before position i+1 .
RaisesInvalid_argument if i+1 is not a valid position in s .
valrindex_from_opt : string->int->char->intoptionrindex_from_optsic is the index of the last occurrence of c in s before position i+1 (if any).
Since 4.05
RaisesInvalid_argument if i+1 is not a valid position in s .
valindex : string->char->intindexsc is String.index_froms0c .
valindex_opt : string->char->intoptionindex_optsc is String.index_from_opts0c .
Since 4.05
valrindex : string->char->intrindexsc is String.rindex_froms(lengths-1)c .
valrindex_opt : string->char->intoptionrindex_optsc is String.rindex_from_opts(lengths-1)c .
Since 4.05
StringsandSequencesvalto_seq : t->charSeq.tto_seqs is a sequence made of the string's characters in increasing order.
Since 4.07
valto_seqi : t->(int*char)Seq.tto_seqis is like StringLabels.to_seq but also tuples the corresponding index.
Since 4.07
valof_seq : charSeq.t->tof_seqs is a string made of the sequence's characters.
Since 4.07
UTFdecodingandvalidationsUTF-8valget_utf_8_uchar : t->int->Uchar.utf_decodeget_utf_8_ucharbi decodes an UTF-8 character at index i in b .
valis_valid_utf_8 : t->boolis_valid_utf_8b is true if and only if b contains valid UTF-8 data.
UTF-16BEvalget_utf_16be_uchar : t->int->Uchar.utf_decodeget_utf_16be_ucharbi decodes an UTF-16BE character at index i in b .
valis_valid_utf_16be : t->boolis_valid_utf_16beb is true if and only if b contains valid UTF-16BE data.
UTF-16LEvalget_utf_16le_uchar : t->int->Uchar.utf_decodeget_utf_16le_ucharbi decodes an UTF-16LE character at index i in b .
valis_valid_utf_16le : t->boolis_valid_utf_16leb is true if and only if b contains valid UTF-16LE data.
Binarydecodingofintegers
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.
valget_uint8 : string->int->intget_uint8bi is b 's unsigned 8-bit integer starting at character index i .
Since 4.13
valget_int8 : string->int->intget_int8bi is b 's signed 8-bit integer starting at character index i .
Since 4.13
valget_uint16_ne : string->int->intget_uint16_nebi is b 's native-endian unsigned 16-bit integer starting at character index i .
Since 4.13
valget_uint16_be : string->int->intget_uint16_bebi is b 's big-endian unsigned 16-bit integer starting at character index i .
Since 4.13
valget_uint16_le : string->int->intget_uint16_lebi is b 's little-endian unsigned 16-bit integer starting at character index i .
Since 4.13
valget_int16_ne : string->int->intget_int16_nebi is b 's native-endian signed 16-bit integer starting at character index i .
Since 4.13
valget_int16_be : string->int->intget_int16_bebi is b 's big-endian signed 16-bit integer starting at character index i .
Since 4.13
valget_int16_le : string->int->intget_int16_lebi is b 's little-endian signed 16-bit integer starting at character index i .
Since 4.13
valget_int32_ne : string->int->int32get_int32_nebi is b 's native-endian 32-bit integer starting at character index i .
Since 4.13
valhash : t->int
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 .
Since 5.0
valseeded_hash : int->t->int
A 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 .
Since 5.0
valget_int32_be : string->int->int32get_int32_bebi is b 's big-endian 32-bit integer starting at character index i .
Since 4.13
valget_int32_le : string->int->int32get_int32_lebi is b 's little-endian 32-bit integer starting at character index i .
Since 4.13
valget_int64_ne : string->int->int64get_int64_nebi is b 's native-endian 64-bit integer starting at character index i .
Since 4.13
valget_int64_be : string->int->int64get_int64_bebi is b 's big-endian 64-bit integer starting at character index i .
Since 4.13
valget_int64_le : string->int->int64get_int64_lebi is b 's little-endian 64-bit integer starting at character index i .
Since 4.13
OCamldoc 2025-06-12 StringLabels(3o)
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