Unordered associative containers (C++): Difference between revisions

Revision as of 15:06, 25 July 2016

Revision as of 18:58, 11 May 2020

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==Usage example==

<sourcesyntaxhighlight lang="cpp">

#include <iostream>

#include <string>

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return 0;

}

</syntaxhighlight>

</source>

==Custom hash functions==

To use custom objects in std::unordered_map, a custom hash function must be defined. This function takes a const reference to the custom type and returns a size_t

<sourcesyntaxhighlight lang="cpp">

#include <unordered_map>

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}

};

</syntaxhighlight>

</source>

The user defined function can be used as is in std::unordered_map, by passing it as a template parameter

<sourcesyntaxhighlight lang="cpp"> std::unordered_map<X,int,hash_X> my_map;</sourcesyntaxhighlight>

Or can be set as the default hash function by specializing the std::hash function

<sourcesyntaxhighlight lang="cpp">

namespace std {

template <>

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//...

std::unordered_map<X,int> my_map;

</syntaxhighlight>

</source>

==References==