Re: STL Map uses hashing?
On 2008-05-31 12:42:50 -0400, "Thomas J. Gritzan"
Pete Becker schrieb:
Creating good-quality hashing functions are not a trivial task at all
(and the subject of continuing extensive research). One cannot expect
the average user to invent a good-quality function without extensive
knowledge and experience on the subject.
Indeed. That's why I've never thought that standardizing hashed
containers was a good idea. There's just too much flexibility, making
them hard to specify well, with the result that naive users can get
horrible performance without knowing why.
But, to answer your question, no, there is no requirement for "high
quality" hashing functions. Implementations will be required to provide
hashing functions for the builtin types, pointers, std::string,
std::u16string, std::u32string, std::wstring, std::error_code, and
What about std::pair<>, tuple<>, etc.?
They're not on the list.
How to do a good hashing function for a combined type like
It depends strongly on how the values are distributed.
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Standard C++ Library Extensions: a Tutorial and Reference
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