Module String
: (moduleStringLabels)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 StdLabels.String(3o)
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