Defined in header <locale> | ||
---|---|---|
public: long hash( const CharT* beg, const CharT* end ) const; | (1) | |
protected: virtual long do_hash( const CharT* beg, const CharT* end ) const; | (2) |
1) Public member function, calls the protected virtual member function
do_hash
of the most derived class. 2) Converts the character sequence
[beg, end)
to an integer value that is equal to the hash obtained for all strings that collate equivalent in this locale (compare()
returns 0
). For two strings that do not collate equivalent, the probability that their hashes are equal should be very small, approaching 1.0/std::numeric_limits<unsigned long>::max()
.Parameters
beg | - | pointer to the first character in the sequence to hash |
end | - | one past the end pointer for the sequence to hash |
Return value
The hash value that respects collation order.
Note
The system-supplied locales normally do not collate two strings as equivalent (compare()
does not return 0
) if basic_string::operator==
returns false
, but a user-installed std::collate
facet may provide different collation rules, for example, it may treat strings as equivalent if they have the same Unicode normalized form.
Example
Demonstrates a locale-aware unordered container.
#include <iostream> #include <string> #include <locale> #include <unordered_set> struct CollateHash { template<typename CharT> std::size_t operator()(const std::basic_string<CharT>& s) const { return std::use_facet<std::collate<CharT>>(std::locale()).hash( &s[0], &s[0] + s.size() ); } }; struct CollateEq { template<typename CharT> bool operator()(const std::basic_string<CharT>& s1, const std::basic_string<CharT>& s2) const { return std::use_facet<std::collate<CharT>>(std::locale()).compare( &s1[0], &s1[0] + s1.size(), &s2[0], &s2[0] + s2.size() ) == 0; } }; int main() { std::locale::global(std::locale("en_US.utf8")); std::wcout.imbue(std::locale()); std::unordered_set<std::wstring, CollateHash, CollateEq> s2 = {L"Foo", L"Bar"}; for(auto& str: s2) std::wcout << str << ' '; std::cout << '\n'; }
Possible output:
Bar Foo
See also
(C++11)(C++11)(C++11)(C++11) | hash support for strings (class template specialization) |
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