Standard Template Library Programmer's Guide

[1] Hash_multimap::iterator is not a mutable iterator, because hash_multimap::value_type is not Assignable. That is, if i is of type hash_multimap::iterator and p is of type hash_multimap::value_type , then *i = p is not a valid expression. However, hash_multimap::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_multimap::const_iterator .

Associative Container, Hashed Associative Container, Pair Associative Container, Multiple Hashed Associative Container, set , map , multiset , multimap , hash_set , hash_map , hash_multiset

Categories: containers, functors

Component type: type

The function object hash is a Hash Function; it is used as the default hash function by all of the Hashed Associative Containers that are included in the STL.

The hash template is only defined for template arguments of type char* , const char* , crope , wrope , and the built-in integral types. [1] If you need a Hash Function with a different argument type, you must either provide your own template specialization or else use a different Hash Function.

int main() {

hash H;

cout << "foo –> " << H("foo") << endl;

cout << "bar –> " << H("bar") << endl;

}

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

Hash Function

T must be a type for which a specialization of hash has been defined. The STL defines the following specializations:

• char*

• const char*

• crope

• wrope

• char

• signed char

• unsigned char

• short

• unsigned short

• int

• unsigned int

• long

• unsigned long

None.

All of hash 's members are defined in the Hash Function requirements. Hash does not introduce any new members.

[1] Technically, what this means is that the actual template hash is an empty class; the member function operator() is defined only in the various specializations.

Hashed Associative Container, Hash Function

Category: utilities

Component type: concept

Several library components, including strings, need to perform operations on characters. A Character Traits class is similar to a function object: it encapsulates some information about a particular character type, and some operations on that type.

Note that every member of a Character Traits class is static. There is never any need to create a Character Traits object, and, in fact, there is no guarantee that creating such objects is possible.

Character Traits is not a refinement of any other concept.

XA type that is a model of Character Traits.

c, c1, c2A value of X 's value type, X::char_type .

e, e1, e2A value of X 's int type, X::int_type .

nA value of type size_t .

p, p1, p2A non-null pointer of type const X::char_type* .

sA non-null pointer of type X::char_type* .

length , find , move , copy , and the range version of assign are linear in n .