Are C++ std::hash implementations always deterministic?

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I know that std::hash<T> are implementation dependent, but are they supposed to be deterministic?

I know if I ran the std::hash<T> function on a value in the same process multiple times, I would get the same output. However, if I restarted the process, would I get the same value? Is there a seed that is used for std::hash? Does it depend on the compiler version, or some other factor?

Is there a guarantee that with an input X I will always get output Y regardless of when the process running was started, the machine, or the compiler version?


No, and documentation clearly says that:

Hash functions are only required to produce the same result for the same input within a single execution of a program; this allows salted hashes that prevent collision DoS attacks.

emphasis is mine. This is since C++14, but we cannot assume that it would work C++11 as such guarantee was not provided explicitly.


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