reversebidirectionaliterator.html

指导程序员合理、高效的进行标准模板库编程。

<tt>reverse_bidirectional_iterator</tt>
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See below.
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<tt>Reference operator*() const</tt>
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 <A href="trivial.html">Trivial Iterator</A>
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The dereference operator
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<tt>reverse_bidirectional_iterator&amp; operator++()</tt>
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 <A href="ForwardIterator.html">Forward Iterator</A>
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Preincrement
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<tt>reverse_bidirectional_iterator operator++(int)</tt>
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 <A href="ForwardIterator.html">Forward Iterator</A>
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Postincrement
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<tt>reverse_bidirectional_iterator&amp; operator--()</tt>
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 <A href="BidirectionalIterator.html">Bidirectional Iterator</A>
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Predecrement
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<tt>reverse_bidirectional_iterator operator--(int)</tt>
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 <A href="BidirectionalIterator.html">Bidirectional Iterator</A>
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Postdecrement
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<tt>bool operator==(const reverse_bidirectional_iterator&amp;, const reverse_bidirectional_iterator&amp;)</tt>
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 <A href="trivial.html">Trivial Iterator</A>
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Compares two iterators for equality.
  This is a global function, not a member function.
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<tt>bidirectional_iterator_tag iterator_category(const reverse_bidirectional_iterator&amp;)</tt>
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 <A href="iterator_tags.html">Iterator tags</A>
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Returns the iterator's category.
  This is a global function, not a member function.
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<tt>T* value_type(const reverse_bidirectional_iterator&amp;)</tt>
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 <A href="iterator_tags.html">Iterator tags</A>
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Returns the iterator's value type.
  This is a global function, not a member function.
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<tt>Distance* distance_type(const reverse_bidirectional_iterator&amp;)</tt>
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 <A href="iterator_tags.html">Iterator tags</A>
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Returns the iterator's distance type.
  This is a global function, not a member function.
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<h3>New members</h3>
These members are not defined 
in the <A href="BidirectionalIterator.html">Bidirectional Iterator</A> requirements,
but are specific to <tt>reverse_bidirectional_iterator</tt>.
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Member
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Description
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<tt>self</tt>
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A typedef for <tt>reverse_bidirectional_iterator&lt;<A href="BidirectionalIterator.html">BidirectionalIterator</A>, T, Reference,
   Distance&gt;</tt>.        
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<tt><A href="BidirectionalIterator.html">BidirectionalIterator</A> base()</tt>
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Returns the current value of the <tt>reverse_bidirectional_iterator</tt>'s base iterator.
   If <tt>ri</tt> is a reverse iterator and <tt>i</tt> is any iterator, 
   the two fundamental identities of reverse iterators can be
   written as
   <tt>reverse_bidirectional_iterator(i).base() == i</tt> and <tt>&amp;*ri == &amp;*(ri.base() - 1)</tt>.
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<tt>reverse_bidirectional_iterator(<A href="BidirectionalIterator.html">BidirectionalIterator</A> i)</tt>
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Constructs a <tt>reverse_bidirectional_iterator</tt> whose base iterator is <tt>i</tt>.
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<h3>Notes</h3>
<P><A name="1">[1]</A>
There isn't really any good reason to have two separate classes:
this separation is purely because of a technical limitation in some of
today's C++ compilers.  If the two classes were combined into one, then there
would be no way to declare the return types of the <A href="iterator_tags.html">iterator tag</A>
functions <tt><A href="iterator_category.html">iterator_category</A></tt>, <tt><A href="distance_type.html" tppabs="http://www.sgi.com/Technology/STL/distance_type.shtml">distance_type</A></tt> and
<tt><A href="value_type.html">value_type</A></tt> correctly.  The <i>iterator traits</i>
class solves this problem: it addresses the same issues as the iterator tag
functions, but in a cleaner and more flexible manner.  Iterator
traits, however, rely on <i>partial specialization</i>, and many
C++ compilers do not yet implement partial specialization.
Once compilers that support partial specialization become more common,
these two different reverse iterator classes will be combined into 
a single class.
<P><A name="2">[2]</A>
The declarations for <tt>rfirst</tt> and <tt>rlast</tt> are written in this
clumsy form simply as an illustration of how to declare a
<tt>reverse_bidirectional_iterator</tt>.  <tt><A href="List.html">List</A></tt> is a 
<A href="ReversibleContainer.html">Reversible Container</A>, so it provides a typedef for the appropriate
instantiation of <tt>reverse_bidirectional_iterator</tt>.  The usual way of
declaring these variables is much simpler: 
<pre>
    list&lt;T&gt;::reverse_bidirectional_iterator rfirst = rbegin();
    list&lt;T&gt;::reverse_bidirectional_iterator rlast = rend(); 
</pre>
<P><A name="3">[3]</A>
Note the implications of this remark.  The variable <tt>rfirst</tt> is
initialized as <tt>reverse_bidirectional_iterator&lt;...&gt; rfirst(V.end());</tt>.  The value
obtained when it is dereferenced, however, is <tt>*(V.end() - 1)</tt>.  This
is a general property: the fundamental identity of reverse iterators
is <tt>&amp;*(reverse_bidirectional_iterator(i)) == &amp;*(i - 1)</tt>.  This code sample shows why
this identity is important: if <tt>[f, l)</tt> is a valid range, then it
allows <tt>[reverse_bidirectional_iterator(l), reverse_bidirectional_iterator(f))</tt> to be a valid
range as well.  Note that the iterator <tt>l</tt> is not part of the range,
but it is required to be dereferenceable or past-the-end.  There is no
requirement that any such iterator precedes <tt>f</tt>.
<h3>See also</h3>
<A href="ReversibleContainer.html">Reversible Container</A>, <A href="ReverseIterator.html" tppabs="http://www.sgi.com/Technology/STL/ReverseIterator.shtml">reverse_iterator</A>,
<A href="BidirectionalIterator.html">Bidirectional Iterator</A>, <A href="iterator_tags.html" tppabs="http://www.sgi.com/Technology/STL/iterator_tags.shtml">iterator tags</A>, <A href="Iterators.html" tppabs="http://www.sgi.com/Technology/STL/Iterators.shtml">Iterator overview</A>

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