Batteries user guide : BatString

String operations.

Given a string s of length l, we call character number in s the index of a character in s. Indexes start at 0, and we will call a character number valid in s if it falls within the range [0...l-1]. A position is the point between two characters or at the beginning or end of the string. We call a position valid in s if it falls within the range [0...l]. Note that character number n is between positions n and n+1.

Two parameters start and len are said to designate a valid substring of s if len >= 0 and start and start+len are valid positions in s.

This module replaces Stdlib's String module.

If you're going to do a lot of string slicing, BatSubstring might be a useful module to represent slices of strings, as it doesn't allocate new strings on every operation.

Author(s): Xavier Leroy (base library), Nicolas Cannasse, David Teller, Edgar Friendly

init l f returns the string of length l with the chars f 0 , f 1 , f 2 ... f (l-1).

Example: String.init 256 char_of_int

The empty string.

Since 3.4.0

is_empty s returns true if s is the empty string, false otherwise.

Usually a tad faster than comparing s with "".

Example (for some string s): if String.is_empty s then "(Empty)" else s

Return a new string that contains the same bytes as the given byte sequence.

Since 3.4.0

Return a new byte sequence that contains the same bytes as the given string.

Since 3.4.0

cat s1 s2 concatenates s1 and s2 (equivalent to s1 ^ s2).

Since 3.4.0
Raises Invalid_argument if the result is longer then than Sys.max_string_length bytes.

for_all p s check if all chars in s satisfy the predicate p.

Since 3.4.0

Return the length (number of characters) of the given string.

String.get s n returns character number n in string s. You can also write s.[n] instead of String.get s n.

Raises Invalid_argument if n not a valid character number in s.

String.set s n c modifies string s in place, replacing the character number n by c. You can also write s.[n] <- c instead of String.set s n c.

Raises Invalid_argument if n is not a valid character number in s.

String.create n returns a fresh string of length n. The string initially contains arbitrary characters.

Raises Invalid_argument if n < 0 or n > Sys.max_string_length.

String.make n c returns a fresh string of length n, filled with the character c.

Raises Invalid_argument if n < 0 or n > Sys.max_string_length.

Return a copy of the given string.

String.sub s start len returns a fresh string of length len, containing the substring of s that starts at position start and has length len.

Raises Invalid_argument if start and len do not designate a valid substring of s.

String.fill s start len c modifies the byte sequence s in place, replacing len characters by c, starting at start.

Raises Invalid_argument if start and len do not designate a valid substring of s.

String.blit src srcoff dst dstoff len copies len characters from string src, starting at character number srcoff, to the byte sequence dst, starting at character number dstoff.

Raises Invalid_argument if srcoff and len do not designate a valid substring of src, or if dstoff and len do not designate a valid substring of dst.

String.concat sep sl concatenates the list of strings sl, inserting the separator string sep between each.

String.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.[String.length s - 1]; ().

Same as String.iter, but the function is applied to the index of the element as first argument (counting from 0), and the character itself as second argument.

Since 4.00.0

String.map f s applies function f in turn to all the characters of s and stores the results in a new string that is returned.

Since 4.00.0

String.mapi f s calls f with each character of s and its index (in increasing index order) and stores the results in a new string that is returned.

Since 4.02.0

Return a copy of the argument, without leading and trailing whitespace (according to BatChar.is_whitespace). The characters regarded as whitespace are: ' ', '\n', '\r', '\t', '\012' and '\026'. If there is no leading nor trailing whitespace character in the argument, return the original string itself, not a copy.

Since 4.00.0

Return a copy of the argument, with special characters represented by escape sequences, following the lexical conventions of OCaml. If there is no special character in the argument, return the original string itself, not a copy. Its inverse function is Scanf.unescaped.

String.index s c returns the character number of the first occurrence of character c in string s.

Raises Not_found if c does not occur in s.

String.index_opt s c returns the index of the first occurrence of character c in string s, or None if c does not occur in s.

Since 2.7.0

String.rindex s c returns the character number of the last occurrence of character c in string s.

Raises Not_found if c does not occur in s.

String.rindex_opt s c returns the index of the last occurrence of character c in string s, or None if c does not occur in s.

Since 2.7.0

String.index_from s i c returns the character number of the first occurrence of character c in string s after or at position i. String.index s c is equivalent to String.index_from s 0 c.

Raises
- Invalid_argument if i is not a valid position in s.
- Not_found if c does not occur in s after position i.

String.index_from_opt s i c returns the index of the first occurrence of character c in string s after position i or None if c does not occur in s after position i.

String.index_opt s c is equivalent to String.index_from_opt s 0 c. Raise Invalid_argument if i is not a valid position in s.

Since 2.7.0

String.rindex_from s i c returns the character number of the last occurrence of character c in string s before position i+1. String.rindex s c is equivalent to String.rindex_from s (String.length s - 1) c.

Raises
- Invalid_argument if i+1 is not a valid position in s.
- Not_found if c does not occur in s before position i+1.

String.rindex_from_opt s i c returns the index of the last occurrence of character c in string s before position i+1 or None if c does not occur in s before position i+1.

String.rindex_opt s c is equivalent to String.rindex_from_opt s (String.length s - 1) c.

Raise Invalid_argument if i+1 is not a valid position in s.

Since 2.7.0

index_after_n chr n str returns the index of the character that comes immediately after the n-th occurrence of chr in str.

Occurrences are numbered from 1: n = 1 returns the index of the character located immediately after the first occurrence of chr.
n = 0 always returns 0.
If the n-th occurrence of chr is the last character of str, returns the length of str.

Since 2.9.0
Raises
- Invalid_argument if n < 0.
- Not_found if there are strictly less than n occurrences of chr in str.

String.contains s c tests if character c appears in the string s.

String.contains_from s start c tests if character c appears in s after position start. String.contains s c is equivalent to String.contains_from s 0 c.

Raises Invalid_argument if start is not a valid position in s.

String.rcontains_from s stop c tests if character c appears in s before position stop+1.

Raises Invalid_argument if stop < 0 or stop+1 is not a valid position in s.

Return a copy of the argument, with all lowercase letters translated to uppercase, including accented letters of the ISO Latin-1 (8859-1) character set.

Return a copy of the argument, with all uppercase letters translated to lowercase, including accented letters of the ISO Latin-1 (8859-1) character set.

Return a copy of the argument, with the first character set to uppercase.

Return a copy of the argument, with the first character set to lowercase.

Return a copy of the argument, with all lowercase letters translated to uppercase, using the US-ASCII character set.

Since 2.5.0

Return a copy of the argument, with all uppercase letters translated to lowercase, using the US-ASCII character set.

Since 2.5.0

Return a copy of the argument, with the first character set to uppercase, using the US-ASCII character set.

Since 2.5.0

Return a copy of the argument, with the first character set to lowercase, using the US-ASCII character set.

Since 2.5.0

An alias for the type of strings.

The comparison function for strings, with the same specification as Pervasives.compare. Along with the type t, this function compare allows the module String to be passed as argument to the functors Set.Make and Map.Make.

Returns an enumeration of the characters of a string. The behaviour is unspecified if the string is mutated while it is enumerated.

Examples: "foo" |> String.enum |> List.of_enum = ['f'; 'o'; 'o'] String.enum "a b c" // ((<>) ' ') |> String.of_enum = "abc"

Creates a string from a character enumeration. Example: ['f'; 'o'; 'o'] |> List.enum |> String.of_enum = "foo"

Returns an enumeration of the characters of a string, from last to first.

Examples: "foo" |> String.backwards |> String.of_enum = "oof" let rev s = String.backwards s |> String.of_enum

Build a string from an enumeration, starting with last character, ending with first.

Converts a list of characters to a string.

Example: ['c'; 'h'; 'a'; 'r'; 's'] |> String.of_list = "chars"

Converts a string to the list of its characters.

Example: String.to_list "string" |> List.interleave ';' |> String.of_list = "s;t;r;i;n;g"

Returns the string representation of an int.

Example: String.of_int 56 = "56" && String.of_int (-1) = "-1"

Returns the string representation of an float.

Example: String.of_float 1.246 = "1.246"

Returns a string containing one given character.

Example: String.of_char 's' = "s"

Returns the integer represented by the given string or

Raises
- Failure if the string does not represent an integer. This follows OCaml's int literal rules, so "0x" prefixes hexadecimal integers, "0o" for octal and "0b" for binary. Underscores within the number are allowed for readability but ignored. Examples: String.to_int "8_480" = String.to_int "0x21_20" try ignore(String.to_int "2,3"); false with Failure _ -> true
- Failure if the string does not represent an integer.

Returns the float represented by the given string or

Raises
- Failure if the string does not represent a float. Decimal points aren't required in the given string, as they are for float literals in OCaml, but otherwise the rules for float literals apply. Examples: String.to_float "12.34e-1" = String.to_float "1.234" String.to_float "1" = 1. try ignore(String.to_float ""); false with Failure _ -> true
- Failure if the string does not represent a float.

map f s returns a string where all characters c in s have been replaced by f c.

Example: String.map Char.uppercase "Five" = "FIVE" *

fold_left f a s is f (... (f (f a s.[0]) s.[1]) ...) s.[n-1]

Examples: String.fold_left (fun li c -> c::li) [] "foo" = ['o';'o';'f'] String.fold_left max 'a' "apples" = 's'

As fold_left, but with the index of the element as additional argument

Since 2.3.0

fold_right f s b is f s.[0] (f s.[1] (... (f s.[n-1] b) ...))

Examples: String.fold_right List.cons "foo" [] = ['f';'o';'o'] String.fold_right (fun c a -> if c = ' ' then a+1 else a) "a b c" 0 = 2

As fold_right, but with the index of the element as additional argument

Since 2.3.0

filter f s returns a copy of string s in which only characters c such that f c = true remain.

Example: String.filter ((<>) ' ') "a b c" = "abc"

filter_map f s calls (f a0) (f a1).... (f an) where a0..an are the characters of s. It returns the string of characters ci such as f ai = Some ci (when f returns None, the corresponding element of s is discarded).

Example: String.filter_map (function 'a'..'z' as c -> Some (Char.uppercase c) | _ -> None) "a b c" = "ABC"

String.iteri f s is equivalent to f 0 s.[0]; f 1 s.[1]; ...; f len s.[len] where len is length of string s. Example:

 let letter_positions word =
      let positions = Array.make 256 [] in
      let count_letter pos c =
        positions.(int_of_char c) <- pos :: positions.(int_of_char c) in
      String.iteri count_letter word;
      Array.mapi (fun c pos -> (char_of_int c, List.rev pos)) positions
      |> Array.to_list
      |> List.filter (fun (c,pos) -> pos <> [])
      in
      letter_positions "hello" = ['e',[1]; 'h',[0]; 'l',[2;3]; 'o',[4] ]

find s x returns the starting index of the first occurrence of string x within string s.

Note This implementation is optimized for short strings.

Raises Not_found if x is not a substring of s. Example: String.find "foobarbaz" "bar" = 3

find_from s pos x behaves as find s x but starts searching at position pos. find s x is equivalent to find_from s 0 x.

Raises
- Not_found if not substring is found
- Invalid_argument if pos is not a valid position in the string. Example: String.find_from "foobarbaz" 4 "ba" = 6

rfind s x returns the starting index of the last occurrence of string x within string s.

Note This implementation is optimized for short strings.

Raises Not_found if x is not a substring of s. Example: String.rfind "foobarbaz" "ba" = 6

rfind_from s pos x behaves as rfind s x but starts searching from the right at position pos + 1. rfind s x is equivalent to rfind_from s (String.length s - 1) x.

Beware, it search between the beginning of the string to the position pos + 1, not between pos + 1 and the end.

Raises
- Not_found if not substring is found
- Invalid_argument if pos is not a valid position in the string. Example: String.rfind_from "foobarbaz" 6 "ba" = 6

find_all s x enumerates positions of s at which x occurs. Example: find_all "aabaabaa" "aba" |> List.of_enum will return the list [1; 4].

Since 2.2.0

count_string s x count how many times x is found in s.

Since 2.9.0

ends_with s x returns true if the string s is ending with x, false otherwise.

Example: String.ends_with "foobarbaz" "rbaz" = true

starts_with s x returns true if s is starting with x, false otherwise.

Example: String.starts_with "foobarbaz" "fooz" = false

Equivalent to starts_with but the prefix is a labelled parameter.

Since 3.4.0

Equivalent to ends_with but the suffix is a labelled parameter.

Since 3.4.0

exists str sub returns true if sub is a substring of str or false otherwise.

Example: String.exists "foobarbaz" "obar" = true

exists_stdlib p str check if at least one char of str satisfies the predicate p.

Since 3.4.0

count_char str c returns the number of times c is used in str.

Returns the same string but without the first n characters. By default n is 1. If n is strictly less than zero

Raises Invalid_argument. If the string has n or less characters, returns the empty string. Example: String.lchop "Weeble" = "eeble" String.lchop ~n:3 "Weeble" = "ble" String.lchop ~n:1000 "Weeble" = ""

Returns the same string but without the last n characters. By default n is 1. If n is strictly less than zero

Raises Invalid_argument. If the string has n or less characters , returns the empty string. Example: String.rchop "Weeble" = "Weebl" String.rchop ~n:3 "Weeble" = "Wee" String.rchop ~n:1000 "Weeble" = ""

Returns the same string but with the first l characters on the left and the first r characters on the right removed. By default, l and r are both 1.

chop ~l ~r s is equivalent to lchop ~n:l (rchop ~n:r s).

Raises Invalid_argument if either l or r is less than zero. Examples: String.chop "\"Weeble\"" = "Weeble" String.chop ~l:2 ~r:3 "01234567" = "234"

Add quotes around a string and escape any quote or escape appearing in that string. This function is used typically when you need to generate source code from a string.

Examples: String.quote "foo" = "\"foo\"" String.quote "\"foo\"" = "\"\\\"foo\\\"\"" String.quote "\n" = "\"\\n\"" etc.

More precisely, the returned string conforms to the OCaml syntax: if printed, it outputs a representation of the input string as an OCaml string litteral.

left r len returns the string containing the len first characters of r. If r contains less than len characters, it returns r.

Examples: String.left "Weeble" 4 = "Weeb" String.left "Weeble" 0 = "" String.left "Weeble" 10 = "Weeble"

right r len returns the string containing the len last characters of r. If r contains less than len characters, it returns r.

Example: String.right "Weeble" 4 = "eble"

tail r pos returns the string containing all but the pos first characters of r

Example: String.tail "Weeble" 4 = "le"

Returns the string without the chars if they are at the beginning or at the end of the string. By default chars are " \t\r\n".

Examples: String.strip " foo " = "foo" String.strip ~chars:" ,()" " boo() bar()" = "boo() bar"

replace_chars f s returns a string where all chars c of s have been replaced by the string returned by f c.

Example: String.replace_chars (function ' ' -> "(space)" | c -> String.of_char c) "foo bar" = "foo(space)bar"

replace ~str ~sub ~by returns a tuple consisting of a boolean and a string where the first occurrence of the string sub within str has been replaced by the string by. The boolean is true if a substitution has taken place.

Example: String.replace "foobarbaz" "bar" "rab" = (true, "foorabbaz")

nreplace ~str ~sub ~by returns a string obtained by iteratively replacing each occurrence of sub by by in str, from right to left. It returns a copy of str if sub has no occurrence in str.

Example: nreplace ~str:"bar foo aaa bar" ~sub:"aa" ~by:"foo" = "bar foo afoo bar"

repeat s n returns s ^ s ^ ... ^ s

Example: String.repeat "foo" 4 = "foofoofoofoo"

rev s returns the reverse of string s

Since 2.1

rev_in_place s mutates the byte sequence s, so that its new value is the mirror of its old one: for instance if s contained "Example!", after the mutation it will contain "!elpmaxE".

Deprecated. Use String.rev_in_place instead

String.split_on_char sep s returns the list of all (possibly empty) substrings of s that are delimited by the sep character.

The function's output 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 (String.concat (String.make 1 sep) (String.split_on_char sep s) = s).
No string in the result contains the sep character.

Note: prior to 2.11.0 split_on_char _ "" used to return an empty list.

Since 2.5.3

split s sep splits the string s between the first occurrence of sep, and returns the two parts before and after the occurrence (excluded).

Raises Not_found if the separator is not found. Examples: String.split "abcabcabc" "bc" = ("a","abcabc") String.split "abcabcabc" "" = ("","abcabcabc")

rsplit s sep splits the string s between the last occurrence of sep, and returns the two parts before and after the occurrence (excluded).

Raises Not_found if the separator is not found. Example: String.rsplit "abcabcabc" "bc" = ("abcabca","")

Deprecated. use BatString.split_on_string

nsplit s sep splits the string s into a list of strings which are separated by sep (excluded). nsplit "" _ returns a single empty string. Note: prior to 2.11.0 nsplit "" _ used to return an empty list.

Example: String.nsplit "abcabcabc" "bc" = ["a"; "a"; "a"; ""]

split_on_string sep s splits the string s into a list of strings which are separated by sep (excluded). split_on_string _ "" returns a single empty string. Note: split_on_string sep s is identical to nsplit s sep but for empty strings.

Example: String.split_on_string "bc" "abcabcabc" = ["a"; "a"; "a"; ""]

Since 2.11.0

Similar to Unix cut. cut_on_char chr n str returns the substring of str located strictly between the n-th occurrence of chr and the n+1-th one.

Occurrences of chr are numbered from 1.
If n = 0, returns the substring from the beginning of str to the first occurrence of chr.
If there are exactly n occurrences of chr in str, returns the substring between the last occurrence of chr and the end of str.
These behaviours cumulate: if n equals 0 and chr is absent from str, returns the full string str.

Remark: cut_on_char can return the empty string. Examples of this behaviour are cut_on_char ',' 1 "foo,,bar" and cut_on_char ',' 0 ",foo".

Since 2.9.0
Raises
- Not_found if there are strictly less than n occurrences of chr in str.
- Invalid_argument if n < 0.

Same as BatString.concat

slice ?first ?last s returns a "slice" of the string which corresponds to the characters s.[first], s.[first+1], ..., s[last-1]. Note that the character at index last is not included! If first is omitted it defaults to the start of the string, i.e. index 0, and if last is omitted is defaults to point just past the end of s, i.e. length s. Thus, slice s is equivalent to copy s.

Negative indexes are interpreted as counting from the end of the string. For example, slice ~last:(-2) s will return the string s, but without the last two characters.

This function never raises any exceptions. If the indexes are out of bounds they are automatically clipped.

Example: String.slice ~first:1 ~last:(-3) " foo bar baz" = "foo bar "

String.splice s off len rep cuts out the section of s indicated by off and len and replaces it by rep

Negative indexes are interpreted as counting from the end of the string. If off+len is greater than length s, the end of the string is used, regardless of the value of len.

If len is zero or negative, rep is inserted at position off without replacing any of s.

Example: String.splice "foo bar baz" 3 5 "XXX" = "fooXXXbaz"

explode s returns the list of characters in the string s.

Example: String.explode "foo" = ['f'; 'o'; 'o']

implode cs returns a string resulting from concatenating the characters in the list cs.

Example: String.implode ['b'; 'a'; 'r'] = "bar"

Iterate on the string, in increasing index order. Modifications of the string during iteration will be reflected in the iterator.

Since 2.10.0 and OCaml 4.07

Iterate on the string, in increasing order, yielding indices along chars

Since 2.10.0 and OCaml 4.07

Create a string from the generator

Since 2.10.0 and OCaml 4.07

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.

Since 3.4.0

get_int8 b i is b's signed 8-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_uint16_ne b i is b's native-endian unsigned 16-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_uint16_be b i is b's big-endian unsigned 16-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_uint16_le b i is b's little-endian unsigned 16-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int16_ne b i is b's native-endian signed 16-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int16_be b i is b's big-endian signed 16-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int16_le b i is b's little-endian signed 16-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int32_ne b i is b's native-endian 32-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int32_be b i is b's big-endian 32-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int32_le b i is b's little-endian 32-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int64_ne b i is b's native-endian 64-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int64_be b i is b's big-endian 64-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

get_int64_le b i is b's little-endian 64-bit integer starting at character index i.

Since 3.4.0 and OCaml 4.08

Ordering function for strings, see BatOrd

Example: String.compare "FOO" "bar" = -1 i.e. "FOO" < "bar"

Compare two strings, case-insensitive.

Example: String.icompare "FOO" "bar" = 1 i.e. "foo" > "bar"

uses icompare as ordering function

Compare two strings, sorting "abc32def" before "abc210abc".

Algorithm: splits both strings into lists of (strings of digits) or (strings of non digits) (["abc"; "32"; "def"] and ["abc"; "210"; "abc"]) Then both lists are compared lexicographically by comparing elements numerically when both are numbers or lexicographically in other cases.

Example: String.numeric_compare "xx32" "xx210" < 0

uses numeric_compare as its ordering function

Edition distance (also known as "Levenshtein distance"). See wikipedia

Since 2.2.0

Print a string.

Example: String.print stdout "foo\n"

Print a string, end the line.

Example: String.println stdout "foo"

Print a string, with quotes as added by the quote function.

String.print_quoted stdout "foo" prints "foo" (with the quotes).

String.print_quoted stdout "\"bar\"" prints "\"bar\"" (with the quotes).

String.print_quoted stdout "\n" prints "\n" (not the escaped character, but '\' then 'n').

Module BatString