How to properly hash the custom struct?

Question

In the C++ language there is the default hash-function template std::hash for the most simple types, like std::string, int, e

Answer 1

boost::hash_combine is something that could help you out here:

namespace std
{
template <>
struct hash
{
    std::size_t operator()(const CustomType& c) const
    {
        std::size_t result = 0;
        boost::hash_combine(result, field1);
        boost::hash_combine(result, field2);
        return result;
    }
};
}

See the boost doc here.