std::collate<CharT>:: hash, std::collate<CharT>:: do_hash
|
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) | |
do_hash
of the most derived class.
[
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 <locale> #include <string> #include <unordered_set> struct CollateHash { template<typename CharT> long 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
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(C++11)
|
hash support for strings
(class template specialization) |