Finds or inserts an element with the specified key. This method is concurrency-safe.
mapped_type& operator( const key_type& _Keyval ); mapped_type& operator( key_type && _Keyval );
If the argument key value is not found, then it is inserted along with the default value of the data type.
operator may be used to insert elements into a map m using m[_Key] = DataValue;, where DataValue is the value of the mapped_type of the element with a key value of _Key.
When using operator to insert elements, the returned reference does not indicate whether an insertion is changing a pre-existing element or creating a new one. The member functions find and insert can be used to determine whether an element with a specified key is already present before an insertion.