String operations.
A string is an immutable data structure that contains a fixed-length sequence of (single-byte) characters. Each character can be accessed in constant time through its index.
Given a string s of length l, we can access each of the l characters of s via its index in the sequence. Indexes start at 0, and we will call an index valid in s if it falls within the range [0...l-1] (inclusive). 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] (inclusive). Note that the character at index 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.
OCaml strings used to be modifiable in place, for instance via the String.set and String.blit functions described below. This usage is deprecated and only possible when the compiler is put in "unsafe-string" mode by giving the -unsafe-string command-line option (which is currently the default for reasons of backward compatibility). This is done by making the types string and bytes (see module Bytes) interchangeable so that functions expecting byte sequences can also accept strings as arguments and modify them.
All new code should avoid this feature and be compiled with the -safe-string command-line option to enforce the separation between the types string and bytes.
String.get s n returns the character at index n in string s. You can also write s.[n] instead of String.get s n.
Raise Invalid_argument if n not a valid index in s.
String.set s n c modifies byte sequence s in place, replacing the byte at index n with c. You can also write s.[n] <- c instead of String.set s n c.
Raise Invalid_argument if n is not a valid index in s.
String.create n returns a fresh byte sequence of length n. The sequence is uninitialized and contains arbitrary bytes.
Raise 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.
Raise Invalid_argument if n < 0 or n > Sys.max_string_length.
String.init n f returns a string of length n, with character i initialized to the result of f i (called in increasing index order).
Raise Invalid_argument if n < 0 or n > Sys.max_string_length.
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.
Raise Invalid_argument if start and len do not designate a valid substring of s.
String.fill s start len c modifies byte sequence s in place, replacing len bytes with c, starting at start.
Raise Invalid_argument if start and len do not designate a valid range of s.
Same as Bytes.blit_string.
String.concat sep sl concatenates the list of strings sl, inserting the separator string sep between each.
Raise Invalid_argument if the result is longer than Sys.max_string_length bytes.
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.
String.map f s applies function f in turn to all the characters of s (in increasing index order) and stores the results in a new string that is returned.
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.
Return a copy of the argument, without leading and trailing whitespace. The characters regarded as whitespace are: ' ', '\012', '\n', '\r', and '\t'. If there is neither leading nor trailing whitespace character in the argument, return the original string itself, not a copy.
Return a copy of the argument, with special characters represented by escape sequences, following the lexical conventions of OCaml. All characters outside the ASCII printable range (32..126) are escaped, as well as backslash and double-quote.
If there is no special character in the argument that needs escaping, return the original string itself, not a copy.
Raise Invalid_argument if the result is longer than Sys.max_string_length bytes.
The function Scanf.unescaped is a left inverse of escaped, i.e. Scanf.unescaped (escaped s) = s for any string s (unless escape s fails).
String.index s c returns the index of the first occurrence of character c in string s.
Raise 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.
String.rindex s c returns the index of the last occurrence of character c in string s.
Raise 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.
String.index_from s i c returns the index of the first occurrence of character c in string s after position i. String.index s c is equivalent to String.index_from s 0 c.
Raise Invalid_argument if i is not a valid position in s. Raise 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.
String.rindex_from s i c returns the index 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.
Raise Invalid_argument if i+1 is not a valid position in s. Raise 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.
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.
Raise 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.
Raise 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, using the ISO Latin-1 (8859-1) character set..
Return a copy of the argument, with the first character set to lowercase, using the ISO Latin-1 (8859-1) character set..
Return a copy of the argument, with all lowercase letters translated to uppercase, using the US-ASCII character set.
Return a copy of the argument, with all uppercase letters translated to lowercase, using the US-ASCII character set.
Return a copy of the argument, with the first character set to uppercase, using the US-ASCII character set.
Return a copy of the argument, with the first character set to lowercase, using the US-ASCII character set.
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.
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:
sep as a separator returns a string equal to the input (String.concat (String.make 1 sep)
(String.split_on_char sep s) = s).sep character.