5.6 KiB
[locale.collate]
28 Text processing library [text]
28.3 Localization library [localization]
28.3.4 Standard locale categories [locale.categories]
28.3.4.5 The collate category [category.collate]
28.3.4.5.1 Class template collate [locale.collate]
28.3.4.5.1.1 General [locale.collate.general]
namespace std {templateclass collate : public locale::facet {public:using char_type = charT; using string_type = basic_string; explicit collate(size_t refs = 0); int compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const; string_type transform(const charT* low, const charT* high) const; long hash(const charT* low, const charT* high) const; static locale::id id; protected:~collate(); virtual int do_compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const; virtual string_type do_transform(const charT* low, const charT* high) const; virtual long do_hash (const charT* low, const charT* high) const; };}
The class collate provides features for use in the collation (comparison) and hashing of strings.
A locale member function template, operator(), uses the collate facet to allow a locale to act directly as the predicate argument for standard algorithms ([algorithms]) and containers operating on strings.
The specializations required in Table 91 ([locale.category]), namely collate and collate<wchar_t>, apply lexicographical ordering ([alg.lex.comparison]).
Each function compares a string of characters *p in the range [low, high).
28.3.4.5.1.2 Members [locale.collate.members]
int compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const;
Returns: do_compare(low1, high1, low2, high2).
string_type transform(const charT* low, const charT* high) const;
Returns: do_transform(low, high).
long hash(const charT* low, const charT* high) const;
Returns: do_hash(low, high).
28.3.4.5.1.3 Virtual functions [locale.collate.virtuals]
int do_compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const;
Returns: 1 if the first string is greater than the second,-1 if less, zero otherwise.
The specializations required in Table 91 ([locale.category]), namely collate and collate<wchar_t>, implement a lexicographical comparison ([alg.lex.comparison]).
string_type do_transform(const charT* low, const charT* high) const;
Returns: A basic_string value that, compared lexicographically with the result of calling transform() on another string, yields the same result as calling do_compare() on the same two strings.226
long do_hash(const charT* low, const charT* high) const;
Returns: An integer value equal to the result of calling hash() on any other string for which do_compare() returns 0 (equal) when passed the two strings.
Recommended practice: The probability that the result equals that for another string which does not compare equal should be very small, approaching (1.0/numeric_limits::max()).
This function is useful when one string is being compared to many other strings.