How Can I Specialize `std::hash::operator()` for Custom Types in C Unordered Containers?

Specializing std::hash::operator() for User-Defined Types in Unordered Containers

To support user-defined key types in std::unordered_set and std::unordered_map, you need to provide the operator==(Key, Key) and a hash functor.

While it would be more convenient to write just std::unordered_set with a default hash for type X, like for built-in types, you can specialize std::hash::operator() to achieve this.

According to C Standard Draft N3242 §20.8.12 [unord.hash] and §17.6.3.4 [hash.requirements], and after consulting various resources, specializing std::hash::operator() in the following way is the correct and only method:

namespace std {
  template <> struct hash<Foo>
  {
    size_t operator()(const Foo &amp; x) const
    {
      /* your code here, e.g. "return hash<int>()(x.value);" */
    }
  };
}

This allows you to add specializations to namespace std and is the recommended way to extend the functionality of standard types for user-defined types.

The above is the detailed content of How Can I Specialize `std::hash::operator()` for Custom Types in C Unordered Containers?. For more information, please follow other related articles on the PHP Chinese website!