[locale.collate.general]

# 28 Text processing library [[text]](./#text)

## 28.3 Localization library [[localization]](localization#locale.collate.general)

### 28.3.4 Standard locale categories [[locale.categories]](locale.categories#locale.collate.general)

#### 28.3.4.5 The collate category [[category.collate]](category.collate#locale.collate.general)

#### 28.3.4.5.1 Class template collate [[locale.collate]](locale.collate#general)

#### 28.3.4.5.1.1 General [locale.collate.general]

[🔗](#lib:collate)

namespace std {template<class charT>class collate : public locale::facet {public:using char_type = charT; using string_type = basic_string<charT>; 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; };}

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L3381)

The class collate<charT> provides features
for use in the collation (comparison) and hashing of strings[.](#1.sentence-1)

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]](algorithms "26 Algorithms library")) and
containers operating on strings[.](#1.sentence-2)

The specializations
required in Table [91](locale.category#tab:locale.category.facets "Table 91: Locale category facets") ([[locale.category]](locale.category "28.3.3.1.2.1 Type locale​::​category")),
namely collate<char> and collate<wchar_t>,
apply lexicographical ordering ([[alg.lex.comparison]](alg.lex.comparison "26.8.11 Lexicographical comparison"))[.](#1.sentence-3)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/text.tex#L3393)

Each function compares a string of characters *p in the range [low, high)[.](#2.sentence-1)