Hash Map in C++ vs Unordered Map

What is the difference between hash_map and unordered_map in C++?

The main difference is that unordered_map is part of the C++11 standard, while hash_map is not part of the standard library. unordered_map uses a hash table for storage, providing average constant time complexity for lookups, insertions, and deletions.

Are there any performance differences between the two?

Yes, unordered_map is generally more efficient due to its standardization and optimizations in modern compilers. hash_map may have different performance characteristics depending on the implementation.

Can I use unordered_map with custom hash functions?

Absolutely! unordered_map allows you to specify a custom hash function and a custom equality function, making it flexible for various data types.

Which one should I use in my project?

It's recommended to use unordered_map for new projects since it's part of the standard library and offers better compatibility and performance.