size_type count(const key_type &x) const
Count the number of key/data pairs having specified key x.
The key to count.
The number of key/data pairs having x as key within the container.
http://www.cplusplus.com/reference/stl/multimap/count/
See of db_map's searching functions group for details about iterator, function version and parameters.
db_map
db_multimap