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<HEAD>
<Title>sparsetable&lt;T, GROUP_SIZE&gt;</Title>
</HEAD>

<BODY>

<p><i>[Note: this document is formatted similarly to the SGI STL
implementation documentation pages, and refers to concepts and classes
defined there.  However, neither this document nor the code it
describes is associated with SGI, nor is it necessary to have SGI's
STL implementation installed in order to use this class.]</i></p>

<H1>sparsetable&lt;T, GROUP_SIZE&gt;</H1>

<p>A <tt>sparsetable</tt> is a <A
href="http://www.sgi.com/tech/stl/RandomAccessContainer.html">Random
Access Container</A> that supports constant time random access to
elements, and constant time insertion and removal of elements.  It
implements the "array" or "table" abstract data type.  The number of
elements in a <tt>sparsetable</tt> is set at constructor time, though
you can change it at any time by calling <tt>resize()</tt>.</p>

<p><tt>sparsetable</tt> is distinguished from other array
implementations, including the default C implementation, in its stingy
use of memory -- in particular, unused array elements require only 1 bit
of disk space to store, rather than <tt>sizeof(T)</tt> bytes -- and by
the ability to save and restore contents to disk.  On the other hand,
this array implementation, while still efficient, is slower than other
array implementations.</p>

<A NAME="assigned">
<p>A <tt>sparsetable</tt> distinguishes between table elements that
have been <i>assigned</i> and those that are <i>unassigned</i>.
Assigned table elements are those that have had a value set via
<tt>set()</tt>, <tt>operator()</tt>, assignment via an iterator, and
so forth.  Unassigned table elements are those that have not had a
value set in one of these ways, or that have been explicitly
unassigned via a call to <tt>erase()</tt> or <tt>clear()</tt>.  Lookup
is valid on both assigned and unassigned table elements; for
unassigned elements, lookup returns the default value
<tt>T()</tt>.</p>
</A>

<p>This class is appropriate for applications that need to store large
arrays in memory, or for applications that need these arrays to be
persistent.</p>


<h3>Example</h3>

<pre>
#include &lt;sparsehash/sparsetable&gt;

using google::sparsetable;      // namespace where class lives by default

sparsetable&lt;int&gt; t(100);
t[5] = 6;
cout &lt;&lt; "t[5] = " &lt;&lt t[5];
cout &lt;&lt; "Default value = " &lt;&lt t[99];
</pre>


<h3>Definition</h3>

Defined in the header <A href="sparsetable">sparsetable</A>.  This
class is not part of the C++ standard.


<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 sparsetable's value type: the type of object that is stored in
   the table.
</TD>
<TD VAlign=top>
   &nbsp;
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>GROUP_SIZE</tt>
</TD>
<TD VAlign=top>
   The number of elements in each sparsetable group (see <A
   HREF="implementation.html">the implementation doc</A> for more details
   on this value).  This almost never need be specified; the default
   template parameter value works well in all situations.
</TD>
<TD VAlign=top>
   &nbsp;
</TD>
</TR>

</table>


<h3>Model of</h3>

<A href="http://www.sgi.com/tech/stl/RandomAccessContainer.html">Random Access Container</A>


<h3>Type requirements</h3>

None, except for those imposed by the requirements of 
<A
href="http://www.sgi.com/tech/stl/RandomAccessContainer.html">Random
Access Container</A>


<h3>Public base classes</h3>

None.


<h3>Members</h3>

<table border>
<TR><TH>Member</TH><TH>Where defined</TH><TH>Description</TH></TR>

<TR>
<TD VAlign=top>
   <tt>value_type</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   The type of object, <tt>T</tt>, stored in the table.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>pointer</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Pointer to <tt>T</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reference</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Reference to <tt>T</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reference</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Const reference to <tt>T</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>size_type</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   An unsigned integral type.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>difference_type</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   A signed integral type.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>iterator</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Iterator used to iterate through a <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_iterator</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Const iterator used to iterate through a <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_iterator</tt>
</TD>
<TD VAlign=top>
   <A
   href="http://www.sgi.com/tech/stl/ReversibleContainer.html">Reversible
   Container</A>
</TD>
<TD VAlign=top>
   Iterator used to iterate backwards through a <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_iterator</tt>
</TD>
<TD VAlign=top>
   <A
   href="http://www.sgi.com/tech/stl/ReversibleContainer.html">Reversible
   Container</A>
</TD>
<TD VAlign=top>
   Const iterator used to iterate backwards through a
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>nonempty_iterator</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Iterator used to iterate through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_nonempty_iterator</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Const iterator used to iterate through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_nonempty_iterator</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Iterator used to iterate backwards through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_nonempty_iterator</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Const iterator used to iterate backwards through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>destructive_iterator</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Iterator used to iterate through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>, erasing elements as it iterates.
   <A href="#1">[1]</A>
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>iterator begin()</tt>
</TD>
<TD VAlign=top>
   <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Returns an <tt>iterator</tt> pointing to the beginning of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>iterator end()</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Returns an <tt>iterator</tt> pointing to the end of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_iterator begin() const</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Returns an <tt>const_iterator</tt> pointing to the beginning of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_iterator end() const</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Returns an <tt>const_iterator</tt> pointing to the end of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_iterator rbegin()</tt>
</TD>
<TD VAlign=top>
   <A
   href="http://www.sgi.com/tech/stl/ReversibleContainer.html">Reversible
   Container</A>
</TD>
<TD VAlign=top>
   Returns a <tt>reverse_iterator</tt> pointing to the beginning of the
   reversed <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_iterator rend()</tt>
</TD>
<TD VAlign=top>
   <A
   href="http://www.sgi.com/tech/stl/ReversibleContainer.html">Reversible
   Container</A>
</TD>
<TD VAlign=top>
   Returns a <tt>reverse_iterator</tt> pointing to the end of the
   reversed <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_iterator rbegin() const</tt>
</TD>
<TD VAlign=top>
   <A
   href="http://www.sgi.com/tech/stl/ReversibleContainer.html">Reversible
   Container</A>
</TD>
<TD VAlign=top>
   Returns a <tt>const_reverse_iterator</tt> pointing to the beginning
   of the reversed <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_iterator rend() const</tt>
</TD>
<TD VAlign=top>
   <A
   href="http://www.sgi.com/tech/stl/ReversibleContainer.html">Reversible
   Container</A>
</TD>
<TD VAlign=top>
   Returns a <tt>const_reverse_iterator</tt> pointing to the end of
   the reversed <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>nonempty_iterator nonempty_begin()</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>nonempty_iterator</tt> pointing to the first
   <A HREF="#assigned">assigned</A> element of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>nonempty_iterator nonempty_end()</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>nonempty_iterator</tt> pointing to the end of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_nonempty_iterator nonempty_begin() const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>const_nonempty_iterator</tt> pointing to the first
   <A HREF="#assigned">assigned</A> element of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_nonempty_iterator nonempty_end() const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>const_nonempty_iterator</tt> pointing to the end of
   the <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_nonempty_iterator nonempty_rbegin()</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>reverse_nonempty_iterator</tt> pointing to the first
   <A HREF="#assigned">assigned</A> element of the reversed
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_nonempty_iterator nonempty_rend()</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>reverse_nonempty_iterator</tt> pointing to the end of
   the reversed <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_nonempty_iterator nonempty_rbegin() const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>const_reverse_nonempty_iterator</tt> pointing to the
   first <A HREF="#assigned">assigned</A> element of the reversed
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_nonempty_iterator nonempty_rend() const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>const_reverse_nonempty_iterator</tt> pointing to the
   end of the reversed <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>destructive_iterator destructive_begin()</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>destructive_iterator</tt> pointing to the first
   <A HREF="#assigned">assigned</A> element of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>destructive_iterator destructive_end()</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>destructive_iterator</tt> pointing to the end of
   the <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>size_type size() const</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Returns the size of the <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>size_type max_size() const</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Returns the largest possible size of the <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool empty() const</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   <tt>true</tt> if the <tt>sparsetable</tt>'s size is <tt>0</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>size_type num_nonempty() const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Returns the number of sparsetable elements that are currently <A
   HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>sparsetable(size_type n)</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Creates a <tt>sparsetable</tt> with <tt>n</tt> elements.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>sparsetable(const sparsetable&amp;)</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   The copy constructor.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>~sparsetable()</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   The destructor.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>sparsetable&amp; operator=(const sparsetable&amp;)</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   The assignment operator
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void swap(sparsetable&amp;)</tt>
</TD>
<TD VAlign=top>
    <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
   Swaps the contents of two sparsetables.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reference operator[](size_type n)</tt>
</TD>
<TD VAlign=top>
    <A
    href="http://www.sgi.com/tech/stl/RandomAccessContainer.html">Random
    Access Container</A>
</TD>
<TD VAlign=top>
   Returns the <tt>n</tt>'th element.  <A href="#2">[2]</A>
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reference operator[](size_type n) const</tt>
</TD>
<TD VAlign=top>
    <A
    href="http://www.sgi.com/tech/stl/RandomAccessContainer.html">Random
    Access Container</A>
</TD>
<TD VAlign=top>
   Returns the <tt>n</tt>'th element.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool test(size_type i) const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   true if the <tt>i</tt>'th element of the <tt>sparsetable</tt> is <A
   HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool test(iterator pos) const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   true if the <tt>sparsetable</tt> element pointed to by <tt>pos</tt>
   is <A HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool test(const_iterator pos) const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   true if the <tt>sparsetable</tt> element pointed to by <tt>pos</tt>
   is <A HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reference get(size_type i) const</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   returns the <tt>i</tt>'th element of the <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reference set(size_type i, const_reference val)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Sets the <tt>i</tt>'th element of the <tt>sparsetable</tt> to value
   <tt>val</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void erase(size_type i)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Erases the <tt>i</tt>'th element of the <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void erase(iterator pos)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Erases the element of the <tt>sparsetable</tt> pointed to by
   <tt>pos</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void erase(iterator first, iterator last)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Erases the elements of the <tt>sparsetable</tt> in the range
   <tt>[first, last)</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void clear()</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Erases all of the elements.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void resize(size_type n)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   Changes the size of sparsetable to <tt>n</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool write_metadata(FILE *fp)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   See below.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool read_metadata(FILE *fp)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   See below.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool write_nopointer_data(FILE *fp)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   See below.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool read_nopointer_data(FILE *fp)</tt>
</TD>
<TD VAlign=top>
   <tt>sparsetable</tt>
</TD>
<TD VAlign=top>
   See below.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <pre>bool operator==(const sparsetable&amp;, const sparsetable&amp;)
</pre>
</TD>
<TD VAlign=top>
    <A
    href="http://www.sgi.com/tech/stl/ForwardContainer.html">Forward
    Container</A>
</TD>
<TD VAlign=top>
   Tests two sparsetables for equality.  This is a global function,
   not a member function.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <pre>bool operator&lt;(const sparsetable&amp;, const sparsetable&amp;)
</pre>
</TD>
<TD VAlign=top>
    <A
    href="http://www.sgi.com/tech/stl/ForwardContainer.html">Forward
    Container</A>
</TD>
<TD VAlign=top>
   Lexicographical comparison.  This is a global function,
   not a member function.
</TD>
</TR>

</table>


<h3>New members</h3>

These members are not defined in the <A
href="http://www.sgi.com/tech/stl/RandomAccessContainer.html">Random
Access Container</A> requirement, but are specific to
<tt>sparsetable</tt>.

<table border>
<TR><TH>Member</TH><TH>Description</TH></TR>

<TR>
<TD VAlign=top>
   <tt>nonempty_iterator</tt>
</TD>
<TD VAlign=top>
   Iterator used to iterate through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_nonempty_iterator</tt>
</TD>
<TD VAlign=top>
   Const iterator used to iterate through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_nonempty_iterator</tt>
</TD>
<TD VAlign=top>
   Iterator used to iterate backwards through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_nonempty_iterator</tt>
</TD>
<TD VAlign=top>
   Const iterator used to iterate backwards through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>destructive_iterator</tt>
</TD>
<TD VAlign=top>
   Iterator used to iterate through the
   <A HREF="#assigned">assigned</A> elements of the
   <tt>sparsetable</tt>, erasing elements as it iterates.
   <A href="#1">[1]</A>
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>nonempty_iterator nonempty_begin()</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>nonempty_iterator</tt> pointing to the first
   <A HREF="#assigned">assigned</A> element of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>nonempty_iterator nonempty_end()</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>nonempty_iterator</tt> pointing to the end of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_nonempty_iterator nonempty_begin() const</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>const_nonempty_iterator</tt> pointing to the first
   <A HREF="#assigned">assigned</A> element of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_nonempty_iterator nonempty_end() const</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>const_nonempty_iterator</tt> pointing to the end of
   the <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_nonempty_iterator nonempty_rbegin()</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>reverse_nonempty_iterator</tt> pointing to the first
   <A HREF="#assigned">assigned</A> element of the reversed
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reverse_nonempty_iterator nonempty_rend()</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>reverse_nonempty_iterator</tt> pointing to the end of
   the reversed <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_nonempty_iterator nonempty_rbegin() const</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>const_reverse_nonempty_iterator</tt> pointing to the
   first <A HREF="#assigned">assigned</A> element of the reversed
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reverse_nonempty_iterator nonempty_rend() const</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>const_reverse_nonempty_iterator</tt> pointing to the
   end of the reversed <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>destructive_iterator destructive_begin()</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>destructive_iterator</tt> pointing to the first
   <A HREF="#assigned">assigned</A> element of the
   <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>destructive_iterator destructive_end()</tt>
</TD>
<TD VAlign=top>
   Returns a <tt>destructive_iterator</tt> pointing to the end of
   the <tt>sparsetable</tt>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>size_type num_nonempty() const</tt>
</TD>
<TD VAlign=top>
   Returns the number of sparsetable elements that are currently <A
   HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool test(size_type i) const</tt>
</TD>
<TD VAlign=top>
   true if the <tt>i</tt>'th element of the <tt>sparsetable</tt> is <A
   HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool test(iterator pos) const</tt>
</TD>
<TD VAlign=top>
   true if the <tt>sparsetable</tt> element pointed to by <tt>pos</tt>
   is <A HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool test(const_iterator pos) const</tt>
</TD>
<TD VAlign=top>
   true if the <tt>sparsetable</tt> element pointed to by <tt>pos</tt>
   is <A HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>const_reference get(size_type i) const</tt>
</TD>
<TD VAlign=top>
   returns the <tt>i</tt>'th element of the <tt>sparsetable</tt>.  If
   the <tt>i</tt>'th element is <A HREF="#assigned">assigned</A>, the
   assigned value is returned, otherwise, the default value
   <tt>T()</tt> is returned.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>reference set(size_type i, const_reference val)</tt>
</TD>
<TD VAlign=top>
   Sets the <tt>i</tt>'th element of the <tt>sparsetable</tt> to value
   <tt>val</tt>, and returns a reference to the <tt>i</tt>'th element
   of the table.  This operation causes the <tt>i</tt>'th element to
   be <A HREF="#assigned">assigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void erase(size_type i)</tt>
</TD>
<TD VAlign=top>
   Erases the <tt>i</tt>'th element of the <tt>sparsetable</tt>.  This
   operation causes the <tt>i</tt>'th element to be <A
   HREF="#assigned">unassigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void erase(iterator pos)</tt>
</TD>
<TD VAlign=top>
   Erases the element of the <tt>sparsetable</tt> pointed to by
   <tt>pos</tt>.  This operation causes the <tt>i</tt>'th element to
   be <A HREF="#assigned">unassigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void erase(iterator first, iterator last)</tt>
</TD>
<TD VAlign=top>
   Erases the elements of the <tt>sparsetable</tt> in the range
   <tt>[first, last)</tt>.  This operation causes these elements to
   be <A HREF="#assigned">unassigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void clear()</tt>
</TD>
<TD VAlign=top>
   Erases all of the elements.  This causes all elements to be
   <A HREF="#assigned">unassigned</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>void resize(size_type n)</tt>
</TD>
<TD VAlign=top>
   Changes the size of sparsetable to <tt>n</tt>.  If <tt>n</tt> is
   greater than the old size, new, <A HREF="#assigned">unassigned</A>
   elements are appended.  If <tt>n</tt> is less than the old size,
   all elements in position &gt;<tt>n</tt> are deleted.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool write_metadata(FILE *fp)</tt>
</TD>
<TD VAlign=top>
   Write hashtable metadata to <tt>fp</tt>.  See <A HREF="#io">below</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool read_metadata(FILE *fp)</tt>
</TD>
<TD VAlign=top>
   Read hashtable metadata from <tt>fp</tt>.  See <A HREF="#io">below</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool write_nopointer_data(FILE *fp)</tt>
</TD>
<TD VAlign=top>
   Write hashtable contents to <tt>fp</tt>.  This is valid only if the
   hashtable key and value are "plain" data.  See <A HREF="#io">below</A>.
</TD>
</TR>

<TR>
<TD VAlign=top>
   <tt>bool read_nopointer_data(FILE *fp)</tt>
</TD>
<TD VAlign=top>
   Read hashtable contents to <tt>fp</tt>.  This is valid only if the
   hashtable key and value are "plain" data.  See <A HREF="#io">below</A>.
</TD>
</TR>

</table>


<h3>Notes</h3>

<P><A name="1">[1]</A>

<tt>sparsetable::destructive_iterator</tt> iterates through a
sparsetable like a normal iterator, but <tt>++it</tt> may delete the
element being iterated past.  Obviously, this iterator can only be
used once on a given table!  One application of this iterator is to
copy data from a sparsetable to some other data structure without
using extra memory to store the data in both places during the
copy.</p>

<P><A name="2">[2]</A>

Since <tt>operator[]</tt> might insert a new element into the
<tt>sparsetable</tt>, it can't possibly be a <tt>const</tt> member
function.  In theory, since it might insert a new element, it should
cause the element it refers to to become <A
HREF="#assigned">assigned</A>.  However, this is undesirable when
<tt>operator[]</tt> is used to examine elements, rather than assign
them.   Thus, as an implementation trick, <tt>operator[]</tt> does not
really return a <tt>reference</tt>.  Instead it returns an object that
behaves almost exactly like a <tt>reference</tt>.  This object,
however, delays setting the appropriate sparsetable element to <A
HREF="#assigned">assigned</A> to when it is actually assigned to.</p>

<p>For a bit more detail: the object returned by <tt>operator[]</tt>
is an opaque type which defines <tt>operator=</tt>, <tt>operator
reference()</tt>, and <tt>operator&</tt>.  The first operator controls
assigning to the value.  The second controls examining the value.  The
third controls pointing to the value.</p>

<p>All three operators perform exactly as an object of type
<tt>reference</tt> would perform.  The only problems that arise is
when this object is accessed in situations where C++ cannot do the
conversion by default.  By far the most common situation is with
variadic functions such as <tt>printf</tt>.  In such situations, you
may need to manually cast the object to the right type:</p>
<pre>
   printf("%d", static_cast&lt;typename table::reference&gt;(table[i]));
</pre>


<h3><A NAME=io>Input/Output</A></h3>

<p>It is possible to save and restore <tt>sparsetable</tt> objects
to disk.  Storage takes place in two steps.  The first writes the
table metadata.  The second writes the actual data.</p>

<p>To write a sparsetable to disk, first call <tt>write_metadata()</tt>
on an open file pointer.  This saves the sparsetable information in a
byte-order-independent format.</p>

<p>After the metadata has been written to disk, you must write the
actual data stored in the sparsetable to disk.  If the value is
"simple" enough, you can do this by calling
<tt>write_nopointer_data()</tt>.  "Simple" data is data that can be
safely copied to disk via <tt>fwrite()</tt>.  Native C data types fall
into this category, as do structs of native C data types.  Pointers
and STL objects do not.</p>

<p>Note that <tt>write_nopointer_data()</tt> does not do any endian
conversion.  Thus, it is only appropriate when you intend to read the
data on the same endian architecture as you write the data.</p>

<p>If you cannot use <tt>write_nopointer_data()</tt> for any reason,
you can write the data yourself by iterating over the
<tt>sparsetable</tt> with a <tt>const_nonempty_iterator</tt> and
writing the key and data in any manner you wish.</p>

<p>To read the hashtable information from disk, first you must create
a <tt>sparsetable</tt> object.  Then open a file pointer to point
to the saved sparsetable, and call <tt>read_metadata()</tt>.  If you
saved the data via <tt>write_nopointer_data()</tt>, you can follow the
<tt>read_metadata()</tt> call with a call to
<tt>read_nopointer_data()</tt>.  This is all that is needed.</p>

<p>If you saved the data through a custom write routine, you must call
a custom read routine to read in the data.  To do this, iterate over
the <tt>sparsetable</tt> with a <tt>nonempty_iterator</tt>; this
operation is sensical because the metadata has already been set up.
For each iterator item, you can read the key and value from disk, and
set it appropriately.  The code might look like this:</p>
<pre>
   for (sparsetable&lt;int*&gt;::nonempty_iterator it = t.nonempty_begin();
        it != t.nonempty_end(); ++it) {
       *it = new int;
       fread(*it, sizeof(int), 1, fp);
   }
</pre>

<p>Here's another example, where the item stored in the sparsetable is
a C++ object with a non-trivial constructor.  In this case, you must
use "placement new" to construct the object at the correct memory
location.</p>
<pre>
   for (sparsetable&lt;ComplicatedCppClass&gt;::nonempty_iterator it = t.nonempty_begin();
        it != t.nonempty_end(); ++it) {
       int constructor_arg;   // ComplicatedCppClass takes an int to construct
       fread(&constructor_arg, sizeof(int), 1, fp);
       new (&(*it)) ComplicatedCppClass(constructor_arg);     // placement new
   }
</pre>


<h3>See also</h3>

<p>The following are SGI STL concepts and classes related to
<tt>sparsetable</tt>.</p>

<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>,
<A href="http://www.sgi.com/tech/stl/RandomAccessContainer.html">Random Access Container</A>,
<tt><A href="sparse_hash_set.html">sparse_hash_set</A></tt>,
<tt><A href="sparse_hash_map.html">sparse_hash_map</A></tt>

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