hash_map was indeed part of the original STL, but was not standardized in C++98. It was still widely available, in slightly incompatible forms, as an extension.

hash_map was indeed part of the original STL, but was not standardized in C++98. It was still widely available, in slightly incompatible forms, as an extension. In C++11 it was standardized with only minor changes (and renamed). The address-preserving property, which precludes an optimal implementation, was considered important to be a near drop-in replacement of std::map.