Multi-map in C++ is an
associative container like map. It internally store elements in key value pair. But unlike map which store only unique keys, multimap can have duplicate keys.
Also, it internally keep elements in sorted order of keys. By default it uses < operator to compare the keys.
Multimap is a container that contains a sorted list of key-value pairs, while permitting multiple entries with the same key. Sorting is done according to the comparison function Compare, applied to the keys. Search, insertion, and removal operations have logarithmic complexity.
This is a companion discussion topic for the original entry at http://iq.opengenus.org/multimap-cpp-stl/