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<Head>
<Title>forward_iterator<T, Distance></Title>
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<H1>forward_iterator<T, Distance></H1>
<Table CellPadding=0 CellSpacing=0 width=100%>
<TR>
<TD Align=left><Img src = "iterators.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD>
<TD Align=right><Img src = "type.gif" Alt="" WIDTH = "194" HEIGHT = "39" ></TD>
</TR>
<TR>
<TD Align=left VAlign=top><b>Category</b>: iterators</TD>
<TD Align=right VAlign=top><b>Component type</b>: type</TD>
</TR>
</Table>
<h3>Description</h3>
<tt>Forward_iterator</tt> is an iterator base class: it is intended that an
iterator that is a model of <A href="ForwardIterator.html">Forward Iterator</A>, and whose value type
and distance type are <tt>T</tt> and <tt>Distance</tt>, may be defined by inheriting from
<tt>forward_iterator<T, Distance></tt> <A href="#1">[1]</A>. <tt>Forward_iterator</tt> is entirely empty: it has no
member functions, member variables, or nested types. It exists solely
to simplify the definition of the functions <tt><A href="iterator_category.html">iterator_category</A></tt>,
<tt><A href="distance_type.html">distance_type</A></tt>, and <tt><A href="value_type.html">value_type</A></tt>.
<h3>Example</h3>
<pre>
class my_forward_iterator : public forward_iterator<double>
{
...
};
</pre>
This declares <tt>my_forward_iterator</tt> to be a <A href="ForwardIterator.html">Forward Iterator</A> whose
value type is <tt>double</tt> and whose distance type is <tt>ptrdiff_t</tt>.
If <tt>Iter</tt> is an object of class <tt>my_forward_iterator</tt>, then
<tt><A href="iterator_category.html">iterator_category</A>(Iter)</tt> will return <tt><A href="forward_iterator_tag.html">forward_iterator_tag</A>()</tt>,
<tt><A href="value_type.html">value_type</A>(Iter)</tt> will return <tt>(double*) 0</tt>, and <tt><A href="distance_type.html">distance_type</A>(Iter)</tt>
will return <tt>(ptrdiff_t*) 0</tt>.
<h3>Definition</h3>
Defined in the standard header <A href="iterator">iterator</A>, and in the
nonstandard backward-compatibility header <A href="iterator.h">iterator.h</A>.
This class is no longer part of the C++ standard, although
it was present in early drafts of the standard. It is retained
in this implementation for backward compatibility.
<h3>Template parameters</h3>
<Table border>
<TR>
<TH>
Parameter
</TH>
<TH>
Description
</TH>
<TH>
Default
</TH>
</TR>
<TR>
<TD VAlign=top>
<tt>T</tt>
</TD>
<TD VAlign=top>
The iterator's value type
</TD>
<TD VAlign=top>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>Distance</tt>
</TD>
<TD VAlign=top>
The iterator's distance type
</TD>
<TD VAlign=top>
<tt>ptrdiff_t</tt>
</TD>
</tr>
</table>
<h3>Model of</h3>
<A href="Assignable.html">Assignable</A>
<h3>Public base classes</h3>
None
<h3>Type requirements</h3>
The distance type must be a signed integral type.
<h3>Public base classes</h3>
None.
<h3>Members</h3>
None.
<h3>New Members</h3>
None.
<h3>Notes</h3>
<P><A name="1">[1]</A>
It is not required that a <A href="ForwardIterator.html">Forward Iterator</A> inherit from the
base <tt>forward_iterator</tt>. It is, however, required that the functions
<tt><A href="iterator_category.html">iterator_category</A></tt>, <tt><A href="distance_type.html">distance_type</A></tt>, and <tt><A href="value_type.html">value_type</A></tt>
be defined for every <A href="ForwardIterator.html">Forward Iterator</A>.
(Or, if you are using the <tt><A href="iterator_traits.html">iterator_traits</A></tt> mechanism, that
<tt>iterator_traits</tt> is properly specialized for every <A href="ForwardIterator.html">Forward Iterator</A>.)
Since those functions are defined for the base <tt>forward_iterator</tt>, the
easiest way to ensure that are defined for a new type is to derive
that class from <tt>forward_iterator</tt> and rely on the derived-to-base
standard conversion of function arguments.
<h3>See also</h3>
The <A href="iterator_tags.html">Iterator Tags</A> overview, <tt><A href="iterator_traits.html">iterator_traits</A></tt>,
<tt><A href="iterator_category.html">iterator_category</A></tt>,
<tt><A href="value_type.html">value_type</A></tt>, <tt><A href="distance_type.html">distance_type</A></tt>,
<tt><A href="input_iterator.html">input_iterator</A></tt>, <tt><A href="output_iterator.html">output_iterator</A></tt>,
<tt><A href="bidirectional_iterator.html">bidirectional_iterator</A></tt>, <tt><A href="random_access_iterator.html">random_access_iterator</A></tt>
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