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

Revision as of 14:21, 10 January 2012

Revision as of 14:23, 10 January 2012

Line 205:

==Custom hash functions==

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

<source lang="cpp">

<code>

struct X{int i,j,k;};

Line 213:

}

};

</codesource>

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

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

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

<source lang="cpp">

<code>

namespace std {

template <>

Line 232:

//...

std::unordered_map<X,int> my_map;

</codesource>

==References==