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+<title>TQCache Class</title>
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+ <a href="index.html">
+<font color="#004faf">Home</font></a>
+ | <a href="classes.html">
+<font color="#004faf">All&nbsp;Classes</font></a>
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+<font color="#004faf">Functions</font></a>
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+<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>TQCache Class Reference</h1>
+
+<p>The TQCache class is a template class that provides a cache based on TQString keys.
+<a href="#details">More...</a>
+<p><tt>#include &lt;<a href="qcache-h.html">ntqcache.h</a>&gt;</tt>
+<p>Inherits <a href="ntqptrcollection.html">TQPtrCollection</a>.
+<p><a href="qcache-members.html">List of all member functions.</a>
+<h2>Public Members</h2>
+<ul>
+<li class=fn><a href="#TQCache-2"><b>TQCache</b></a> ( int&nbsp;maxCost = 100, int&nbsp;size = 17, bool&nbsp;caseSensitive = TRUE )</li>
+<li class=fn><a href="#~TQCache"><b>~TQCache</b></a> ()</li>
+<li class=fn>int <a href="#maxCost"><b>maxCost</b></a> () const</li>
+<li class=fn>int <a href="#totalCost"><b>totalCost</b></a> () const</li>
+<li class=fn>void <a href="#setMaxCost"><b>setMaxCost</b></a> ( int&nbsp;m )</li>
+<li class=fn>virtual uint <a href="#count"><b>count</b></a> () const</li>
+<li class=fn>uint <a href="#size"><b>size</b></a> () const</li>
+<li class=fn>bool <a href="#isEmpty"><b>isEmpty</b></a> () const</li>
+<li class=fn>virtual void <a href="#clear"><b>clear</b></a> ()</li>
+<li class=fn>bool <a href="#insert"><b>insert</b></a> ( const&nbsp;TQString&nbsp;&amp;&nbsp;k, const&nbsp;type&nbsp;*&nbsp;d, int&nbsp;c = 1, int&nbsp;p = 0 )</li>
+<li class=fn>bool <a href="#remove"><b>remove</b></a> ( const&nbsp;TQString&nbsp;&amp;&nbsp;k )</li>
+<li class=fn>type * <a href="#take"><b>take</b></a> ( const&nbsp;TQString&nbsp;&amp;&nbsp;k )</li>
+<li class=fn>type * <a href="#find"><b>find</b></a> ( const&nbsp;TQString&nbsp;&amp;&nbsp;k, bool&nbsp;ref = TRUE ) const</li>
+<li class=fn>type * <a href="#operator[]"><b>operator[]</b></a> ( const&nbsp;TQString&nbsp;&amp;&nbsp;k ) const</li>
+<li class=fn>void <a href="#statistics"><b>statistics</b></a> () const</li>
+</ul>
+<h2>Important Inherited Members</h2>
+<ul>
+<li class=fn>bool <a href="#autoDelete"><b>autoDelete</b></a> () const</li>
+<li class=fn>void <a href="#setAutoDelete"><b>setAutoDelete</b></a> ( bool&nbsp;enable )</li>
+</ul>
+<hr><a name="details"></a><h2>Detailed Description</h2>
+
+
+The TQCache class is a template class that provides a cache based on <a href="ntqstring.html">TQString</a> keys.
+<p>
+
+<p>
+<p> A cache is a least recently used (LRU) list of cache items. Each
+cache item has a key and a certain cost. The sum of item costs,
+<a href="#totalCost">totalCost</a>(), never exceeds the maximum cache cost, <a href="#maxCost">maxCost</a>(). If
+inserting a new item would cause the total cost to exceed the
+maximum cost, the least recently used items in the cache are
+removed.
+<p> TQCache is a template class. TQCache&lt;X&gt; defines a cache that
+operates on pointers to X, or X*.
+<p> Apart from <a href="#insert">insert</a>(), by far the most important function is <a href="#find">find</a>()
+(which also exists as <a href="#operator[]">operator[]</a>()). This function looks up an
+item, returns it, and by default marks it as being the most
+recently used item.
+<p> There are also methods to <a href="#remove">remove</a>() or <a href="#take">take</a>() an object from the
+cache. Calling <a href="ntqptrcollection.html#setAutoDelete">setAutoDelete</a>(TRUE) for a cache tells it to delete
+items that are removed. The default is to not delete items when
+they are removed (i.e., remove() and take() are equivalent).
+<p> When inserting an item into the cache, only the pointer is copied,
+not the item itself. This is called a <a href="shclass.html#shallow-copy">shallow copy</a>. It is possible
+to make the cache copy all of the item's data (known as a <a href="shclass.html#deep-copy">deep copy</a>) when an item is inserted. insert() calls the virtual
+function <a href="ntqptrcollection.html#newItem">TQPtrCollection::newItem</a>() for the item to be inserted.
+Inherit a cache and reimplement <a href="ntqptrcollection.html#newItem">newItem</a>() if you want deep copies.
+<p> When removing a cache item, the virtual function
+<a href="ntqptrcollection.html#deleteItem">TQPtrCollection::deleteItem</a>() is called. The default
+implementation deletes the item if auto-deletion is enabled, and
+does nothing otherwise.
+<p> There is a <a href="qcacheiterator.html">TQCacheIterator</a> that can be used to traverse the items
+in the cache in arbitrary order.
+<p> In TQCache, the cache items are accessed via <a href="ntqstring.html">TQString</a> keys, which
+are Unicode strings. If you want to use non-Unicode, plain 8-bit
+<tt>char*</tt> keys, use the <a href="ntqasciicache.html">TQAsciiCache</a> template. A TQCache has the
+same performance as a TQAsciiCache.
+<p> <p>See also <a href="qcacheiterator.html">TQCacheIterator</a>, <a href="ntqasciicache.html">TQAsciiCache</a>, <a href="ntqintcache.html">TQIntCache</a>, <a href="collection.html">Collection Classes</a>, and <a href="tools.html">Non-GUI Classes</a>.
+
+<hr><h2>Member Function Documentation</h2>
+<h3 class=fn><a name="TQCache-2"></a>TQCache::TQCache ( int&nbsp;maxCost = 100, int&nbsp;size = 17, bool&nbsp;caseSensitive = TRUE )
+</h3>
+
+<p> Constructs a cache whose contents will never have a total cost
+greater than <em>maxCost</em> and which is expected to contain less than
+<em>size</em> items.
+<p> <em>size</em> is actually the size of an internal hash array; it's
+usually best to make it a <a href="primes.html#prime">prime</a> number and at least 50% bigger
+than the largest expected number of items in the cache.
+<p> Each inserted item has an associated cost. When inserting a new
+item, if the total cost of all items in the cache will exceed <em>maxCost</em>, the cache will start throwing out the older (least
+recently used) items until there is enough room for the new item
+to be inserted.
+<p> If <em>caseSensitive</em> is TRUE (the default), the cache keys are case
+sensitive; if it is FALSE, they are case-insensitive.
+Case-insensitive comparison considers all Unicode letters.
+
+<h3 class=fn><a name="~TQCache"></a>TQCache::~TQCache ()
+</h3>
+
+<p> Removes all items from the cache and destroys it. All iterators
+that access this cache will be reset.
+
+<h3 class=fn>bool <a name="autoDelete"></a>TQPtrCollection::autoDelete () const
+</h3>
+
+<p> Returns the setting of the auto-delete option. The default is FALSE.
+<p> <p>See also <a href="ntqptrcollection.html#setAutoDelete">setAutoDelete</a>().
+
+<h3 class=fn>void <a name="clear"></a>TQCache::clear ()<tt> [virtual]</tt>
+</h3>
+
+<p> Removes all items from the cache and deletes them if auto-deletion
+has been enabled.
+<p> All cache iterators that operate this on cache are reset.
+<p> <p>See also <a href="#remove">remove</a>() and <a href="#take">take</a>().
+
+<p>Reimplemented from <a href="ntqptrcollection.html#clear">TQPtrCollection</a>.
+<h3 class=fn>uint <a name="count"></a>TQCache::count () const<tt> [virtual]</tt>
+</h3>
+
+<p> Returns the number of items in the cache.
+<p> <p>See also <a href="#totalCost">totalCost</a>().
+
+<p>Reimplemented from <a href="ntqptrcollection.html#count">TQPtrCollection</a>.
+<h3 class=fn>type * <a name="find"></a>TQCache::find ( const&nbsp;<a href="ntqstring.html">TQString</a>&nbsp;&amp;&nbsp;k, bool&nbsp;ref = TRUE ) const
+</h3>
+
+<p> Returns the item associated with key <em>k</em>, or 0 if the key does
+not exist in the cache. If <em>ref</em> is TRUE (the default), the item
+is moved to the front of the least recently used list.
+<p> If there are two or more items with equal keys, the one that was
+inserted last is returned.
+
+<h3 class=fn>bool <a name="insert"></a>TQCache::insert ( const&nbsp;<a href="ntqstring.html">TQString</a>&nbsp;&amp;&nbsp;k, const&nbsp;type&nbsp;*&nbsp;d, int&nbsp;c = 1, int&nbsp;p = 0 )
+</h3>
+
+<p> Inserts the item <em>d</em> into the cache with key <em>k</em> and associated
+cost, <em>c</em>. Returns TRUE if it is successfully inserted; otherwise
+returns FALSE.
+<p> The cache's size is limited, and if the total cost is too high,
+TQCache will remove old, least recently used items until there is
+room for this new item.
+<p> The parameter <em>p</em> is internal and should be left at the default
+value (0).
+<p> <b>Warning:</b> If this function returns FALSE (which could happen, e.g.
+if the cost of this item alone exceeds <a href="#maxCost">maxCost</a>()) you must delete
+<em>d</em> yourself. Additionally, be very careful about using <em>d</em>
+after calling this function because any other insertions into the
+cache, from anywhere in the application or within TQt itself, could
+cause the object to be discarded from the cache and the pointer to
+become invalid.
+
+<h3 class=fn>bool <a name="isEmpty"></a>TQCache::isEmpty () const
+</h3>
+
+<p> Returns TRUE if the cache is empty; otherwise returns FALSE.
+
+<h3 class=fn>int <a name="maxCost"></a>TQCache::maxCost () const
+</h3>
+
+<p> Returns the maximum allowed total cost of the cache.
+<p> <p>See also <a href="#setMaxCost">setMaxCost</a>() and <a href="#totalCost">totalCost</a>().
+
+<h3 class=fn>type * <a name="operator[]"></a>TQCache::operator[] ( const&nbsp;<a href="ntqstring.html">TQString</a>&nbsp;&amp;&nbsp;k ) const
+</h3>
+
+<p> Returns the item associated with key <em>k</em>, or 0 if <em>k</em> does not
+exist in the cache, and moves the item to the front of the least
+recently used list.
+<p> If there are two or more items with equal keys, the one that was
+inserted last is returned.
+<p> This is the same as <a href="#find">find</a>( k, TRUE ).
+<p> <p>See also <a href="#find">find</a>().
+
+<h3 class=fn>bool <a name="remove"></a>TQCache::remove ( const&nbsp;<a href="ntqstring.html">TQString</a>&nbsp;&amp;&nbsp;k )
+</h3>
+
+<p> Removes the item associated with <em>k</em>, and returns TRUE if the
+item was present in the cache; otherwise returns FALSE.
+<p> The item is deleted if auto-deletion has been enabled, i.e., if
+you have called <a href="ntqptrcollection.html#setAutoDelete">setAutoDelete</a>(TRUE).
+<p> If there are two or more items with equal keys, the one that was
+inserted last is removed.
+<p> All iterators that refer to the removed item are set to point to
+the next item in the cache's traversal order.
+<p> <p>See also <a href="#take">take</a>() and <a href="#clear">clear</a>().
+
+<h3 class=fn>void <a name="setAutoDelete"></a>TQPtrCollection::setAutoDelete ( bool&nbsp;enable )
+</h3>
+
+<p> Sets the collection to auto-delete its contents if <em>enable</em> is
+TRUE and to never delete them if <em>enable</em> is FALSE.
+<p> If auto-deleting is turned on, all the items in a collection are
+deleted when the collection itself is deleted. This is convenient
+if the collection has the only pointer to the items.
+<p> The default setting is FALSE, for safety. If you turn it on, be
+careful about copying the collection - you might find yourself
+with two collections deleting the same items.
+<p> Note that the auto-delete setting may also affect other functions
+in subclasses. For example, a subclass that has a <a href="#remove">remove</a>()
+function will remove the item from its data structure, and if
+auto-delete is enabled, will also delete the item.
+<p> <p>See also <a href="ntqptrcollection.html#autoDelete">autoDelete</a>().
+
+<p>Examples: <a href="grapher-nsplugin-example.html#x2769">grapher/grapher.cpp</a>, <a href="scribble-example.html#x924">scribble/scribble.cpp</a>, and <a href="bigtable-example.html#x1291">table/bigtable/main.cpp</a>.
+<h3 class=fn>void <a name="setMaxCost"></a>TQCache::setMaxCost ( int&nbsp;m )
+</h3>
+
+<p> Sets the maximum allowed total cost of the cache to <em>m</em>. If the
+current total cost is greater than <em>m</em>, some items are deleted
+immediately.
+<p> <p>See also <a href="#maxCost">maxCost</a>() and <a href="#totalCost">totalCost</a>().
+
+<h3 class=fn>uint <a name="size"></a>TQCache::size () const
+</h3>
+
+<p> Returns the size of the hash array used to implement the cache.
+This should be a bit bigger than <a href="#count">count</a>() is likely to be.
+
+<h3 class=fn>void <a name="statistics"></a>TQCache::statistics () const
+</h3>
+
+<p> A debug-only utility function. Prints out cache usage, hit/miss,
+and distribution information using <a href="ntqapplication.html#qDebug">qDebug</a>(). This function does
+nothing in the release library.
+
+<h3 class=fn>type * <a name="take"></a>TQCache::take ( const&nbsp;<a href="ntqstring.html">TQString</a>&nbsp;&amp;&nbsp;k )
+</h3>
+
+<p> Takes the item associated with <em>k</em> out of the cache without
+deleting it, and returns a pointer to the item taken out, or 0
+if the key does not exist in the cache.
+<p> If there are two or more items with equal keys, the one that was
+inserted last is taken.
+<p> All iterators that refer to the taken item are set to point to the
+next item in the cache's traversal order.
+<p> <p>See also <a href="#remove">remove</a>() and <a href="#clear">clear</a>().
+
+<h3 class=fn>int <a name="totalCost"></a>TQCache::totalCost () const
+</h3>
+
+<p> Returns the total cost of the items in the cache. This is an
+integer in the range 0 to <a href="#maxCost">maxCost</a>().
+<p> <p>See also <a href="#setMaxCost">setMaxCost</a>().
+
+<!-- eof -->
+<hr><p>
+This file is part of the <a href="index.html">TQt toolkit</a>.
+Copyright &copy; 1995-2007
+<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
+<table width=100% cellspacing=0 border=0><tr>
+<td>Copyright &copy; 2007
+<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
+<td align=right><div align=right>TQt 3.3.8</div>
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+</html>