Standard Template Library Programmer's Guide

[1] 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_set::const_iterator .

Associative Container, Hashed Associative Container, Simple Associative Container, Unique Hashed Associative Container, set , map , multiset , multimap , hash_map , hash_multiset , hash_multimap

Category: containers

Component type: type

Hash_map is a Hashed Associative Container that associates objects of type Key with objects of type Data . Hash_map is a Pair Associative Container, meaning that its value type is pair . It is also a Unique Associative Container, meaning that no two elements have keys that compare equal using EqualKey .

Looking up an element in a hash_map by its key is efficient, so hash_map is useful for "dictionaries" where the order of elements is irrelevant. If it is important for the elements to be in a particular order, however, then map is more appropriate.

struct eqstr {

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

return strcmp(s1, s2) == 0;

}

};

int main() {

hash_map, eqstr> months;

months["january"] = 31;

months["february"] = 28;

months["march"] = 31;

months["april"] = 30;

months["may"] = 31;

months["june"] = 30;

months["july"] = 31;

months["august"] = 31;

months["september"] = 30;

months["october"] = 31;

months["november"] = 30;

months["december"] = 31;

cout << "september –> " << months["september"] << endl;

cout << "april –> " << months["april"] << endl;

cout << "june –> " << months["june"] << endl;

cout << "november –> " << months["november"] << endl;

}

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

Unique Hashed Associative Container, Pair 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.

These members are not defined in the Unique Hashed Associative Container and Pair Associative Container requirements, but are specific to hash_map .