Standard Template Library Programmer's Guide

Component type: type

Description

Multimap is a Sorted Associative Container that associates objects of type Key with objects of type Data. multimap is a Pair Associative Container, meaning that its value type is pair<const Key, Data>. It is also a Multiple Associative Container, meaning that there is no limit on the number of elements with the same key.

Multimap has the important property that inserting a new element into a multimap does not invalidate iterators that point to existing elements. Erasing an element from a multimap also does not invalidate any iterators, except, of course, for iterators that actually point to the element that is being erased.

Example

struct ltstr {
 bool operator()(const char* s1, const char* s2) const {
  return strcmp(s1, s2) < 0;
 }
};
int main() {
 multimap<const char*, int, ltstr> m;
 m.insert(pair<const char* const, int>('a', 1));
 m.insert(pair<const char* const, int>('c', 2));
 m.insert(pair<const char* const, int>('b', 3));
 m.insert(pair<const char* const, int>('b', 4));
 m.insert(pair<const char* const, int>('a', 5));
 m.insert(pair<const char* const, int>('b', 6));
 cout << 'Number of elements with key a: ' << m.count('a') << endl;
 cout << 'Number of elements with key b: ' << m.count('b') << endl;
 cout << 'Number of elements with key c: ' << m.count('c') << endl;
 cout << 'Elements in m: ' << endl;
 for (multimap<const char*, int, ltstr>::iterator it = m.begin(); it != m.end(); ++it)
  cout << ' [' << (*it).first << ', ' << (*it).second << ']' << endl;
}

Definition

Defined in the standard header map, and in the nonstandard backward-compatibility header multimap.h.

Template parameters

Parameter	Description	Default
Key	The multimap's key type. This is also defined as multimap::key_type.
Data	The multimap's data type. This is also defined as multimap::data_type.
Compare	The key comparison function, a Strict Weak Ordering whose argument type is key_type; it returns true if its first argument is less than its second argument, and false otherwise. This is also defined as multimap::key_compare.	less<Key>
Alloc	The multimap 's allocator, used for all internal memory management.	alloc

Model of

Multiple Sorted Associative Container, Pair Associative Container

Type requirements

• Data is Assignable.

• Compare is a Strict Weak Ordering whose argument type is Key.

• Alloc is an Allocator.

Public base classes

None.

Members

Member	Where defined	Description
key_type	Associative Container	The multimap 's key type, Key.
data_type	Pair Associative Container	The type of object associated with the keys.