Standard C++	Library
 		 Copyright 1996, Rogue Wave Software, Inc.

 NAME

   Bidirectional_Iterators  - An	iterator that can both read and	write
   and can traverse a container in both directions

 DESCRIPTION

   For a	complete discussion of iterators, see the Iterators section of
   this reference.

   Iterators are	a generalization of pointers that allow	a C++ program
   to uniformly interact with different data structures.  Bidirectional
   iterators can move both	forwards and backwards through a
   container, and	have the ability to both read and write data.
   These iterators	satisfy	the requirements	listed below.

   KEY TO ITERATOR REQUIREMENTS

   The following	key pertains to	the iterator descriptions listed below:

   a and	b   values of type X

   n   value of distance	type

   u, Distance, tmp and m   identifiers

   r   value of type X&

   t   value of type T

   REQUIREMENTS FOR BIDIRECTIONAL ITERATORS

   A bidirectional iterator must	meet all the requirements listed
   below.	 Note that most of these requirements are also the
   requirements for	forward iterators.

   X u	u might	have a singular	value

   X()	X() might be singular

   X(a)	 copy constructor, a ==	X(a).

   X u(a)   copy	constructor, u == a

   X u =	a   assignment,	u == a

   a == b, a != b   return value	convertible to bool

   a->m	 equivalent to (*a).m

   *a   return value convertible	to T&

   ++r	returns	X&

   r++	return value convertible to const X&

   *r++	 returns T&

   --r	returns	X&

   r--	return value convertible to const X&

   *r--	 returns T&

   Like forward iterators, bidirectional	iterators have the condition
   that a == b implies *a== *b.

   There	are no restrictions on the number of passes an algorithm may
   make through the structure.

 SEE ALSO

   Containers, Iterators, Forward Iterators

 STANDARDS CONFORMANCE
   ANSI X3J16/ISO WG21 Joint C++	Committee