Standard Template Library Programmer's Guide

[1] Hash_map::iterator is not a mutable iterator, because hash_map::value_type is not Assignable. That is, if i is of type hash_map::iterator and p is of type hash_map::value_type , then *i = p is not a valid expression. However, hash_map::iterator isn't a constant iterator either, because it can be used to modify the object that it points to. Using the same notation as above, (*i).second = p is a valid expression.

[2] This member function relies on member template functions, which at present (early 1998) are not supported by all compilers. If your compiler supports member templates, you can call this function with any type of input iterator. If your compiler does not yet support member templates, though, then the arguments must either be of type const value_type* or of type hash_map::const_iterator .

[3] Since operator[] might insert a new element into the hash_map , it can't possibly be a const member function. Note that the definition of operator[] is extremely simple: m[k] is equivalent to (*((m.insert(value_type(k, data_type()))).first)).second . Strictly speaking, this member function is unnecessary: it exists only for convenience.

Associative Container, Hashed Associative Container, Pair Associative Container, Unique Hashed Associative Container, set , map, multiset , multimap , hash_set , hash_multiset , hash_multimap

Category: containers

Component type: type

Hash_multiset is a Hashed Associative Container that stores objects of type Key . Hash_multiset is a simple associative container, meaning that its value type, as well as its key type, is Key . It is also a Multiple Associative Container, meaning that two or more elements may compare equal using the Binary Predicate EqualKey .

Hash_multiset is useful in applications where it is important to be able to search for an element quickly. If it is important for the elements to be in a particular order, however, then multiset is more appropriate.

struct eqstr {

bool operator()(const char* s1, const char* s2) const {

return strcmp(s1, s2) == 0;

}

};

void lookup(const hash_multiset, eqstr>& Set, const char* word) {

int n_found = Set.count(word);

cout << word << ": " << n_found << " " << (n_found == 1 ? "instance" : "instances") << endl;

}

int main() {

hash_multiset, eqstr> Set;

Set.insert("mango");

Set.insert("kiwi");

Set.insert("apple");

Set.insert("kiwi");

Set.insert("mango");

Set.insert("mango");

Set.insert("apricot");

Set.insert("banana");

Set.insert("mango");

lookup(Set, "mango");

lookup(Set, "apple");

lookup(Set, "durian");

}

Defined in the header hash_set, and in the backward-compatibility header hash_set.h. This class is an SGI extension; it is not part of the C++ standard.

Multiple Hashed Associative Container, Simple Associative Container

• Key is assignable.

• EqualKey is a Binary Predicate whose argument type is Key .

• EqualKey is an equivalence relation.

• Alloc is an Allocator.

None.

All of hash_multiset 's members are defined in the Multiple Hashed Associative Container and Simple Associative Container requirements. Hash_multiset does not introduce any new members.