Difference between hash_map and unordered_map?
I recently discovered that the implementation of the hash map in C++ will be called unordered_map
.
When I looked up why they weren't just using hash_map
, I discovered that apparently there are compatibility issues with the implementation of hash_map
that unordered_map
resolves (more about i开发者_开发问答t here).
That wiki page doesn't give much more information so I wondering if anyone knew some of the issues with hash_map
that unordered_map
resolves.
Since there was no hash table defined in the C++ standard library, different implementors of the standard libraries would provide a non-standard hash table often named hash_map
. Because these implementations were not written following a standard they all had subtle differences in functionality and performance guarantees.
Starting with C++11 a hash table implementation has been added to the C++ standard library standard. It was decided to use an alternate name for the class to prevent collisions with these non-standard implementations and to prevent inadvertent use of the new class by developers who had hash_table
in their code.
The chosen alternate name is unordered_map
which really is more descriptive as it hints at the class's map interface and the unordered nature of its elements.
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