src/third_party/google-sparsehash/doc/sparsetable.html - incubator-pagespeed-debian - Git at Google

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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;google/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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