How Can I Effectively Combine Hash Values in C 0x?

Hash Value Combination in C 0x

In C 0x, the addition of hash<...>(...) introduces a valuable tool for manipulating hash values. However, the absence of a hash_combine function similar to that provided in Boost has left programmers seeking an alternative approach. This article explores a clean implementation using C 0x's xor_combine.

The crux of the solution lies in imitating the implementation from Boost:

template <class T>
inline void hash_combine(std::size_t& seed, const T& v)
{
    std::hash<T> hasher;
    seed ^= hasher(v) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
}

This function employs std::hash to generate a hash value for the input value v. It then combines this hash value with an additional constant and the existing seed using a series of bitwise operations, resulting in a robust hash that effectively combines multiple elements.

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