Hashing pointers as Keys for unordered_map in C++ STL

c++ hash stl unordered-map
Ammar Husain picture Ammar Husain · Aug 4, 2014 · Viewed 11.7k times · Source

I posted a similar quetion regarding using pointers as Keys on maps in C++ STL. How are pointers hashed in unordered_maps when used as Keys. More specifically if I define:

std::unordered_map< CustomClass*, int > foo;

Would the default C++ std::hash implementation work to handle these pointers? Is it safe to use? Is this good practice?

Answer

Mark Ransom picture Mark Ransom · Aug 4, 2014

std::hash<T*> is defined but the details of how it operates are implementation dependent. It will certainly be safe to use, and I'd consider it good practice - as long as it's the pointer you need as the key, and not the object contents itself.

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