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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"><!-- /home/reggie/tmp/qt-3.0-reggie-5401/qt-x11-commercial-3.0.5/doc/qcache.doc:42 --><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>QCache Class</title><style type="text/css"><!--h3.fn,span.fn { margin-left: 1cm; text-indent: -1cm; }a:link { color: #004faf; text-decoration: none }a:visited { color: #672967; text-decoration: none }body { background: #ffffff; color: black; }--></style></head><body><table border="0" cellpadding="0" cellspacing="0" width="100%"><tr bgcolor="#E5E5E5"><td valign=center> <a href="index.html"><font color="#004faf">Home</font></a> | <a href="classes.html"><font color="#004faf">All Classes</font></a> | <a href="mainclasses.html"><font color="#004faf">Main Classes</font></a> | <a href="annotated.html"><font color="#004faf">Annotated</font></a> | <a href="groups.html"><font color="#004faf">Grouped Classes</font></a> | <a href="functions.html"><font color="#004faf">Functions</font></a></td><td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QCache Class Reference</h1><p>The QCache class is a template class that provides a cache based on QString keys.<a href="#details">More...</a><p><tt>#include <<a href="qcache-h.html">qcache.h</a>></tt><p>Inherits <a href="qptrcollection.html">QPtrCollection</a>.<p><a href="qcache-members.html">List of all member functions.</a><h2>Public Members</h2><ul><li><div class=fn><a href="#QCache-2"><b>QCache</b></a> ( int maxCost = 100, int size = 17, bool caseSensitive = TRUE )</div></li><li><div class=fn><a href="#~QCache"><b>~QCache</b></a> ()</div></li><li><div class=fn>int <a href="#maxCost"><b>maxCost</b></a> () const</div></li><li><div class=fn>int <a href="#totalCost"><b>totalCost</b></a> () const</div></li><li><div class=fn>void <a href="#setMaxCost"><b>setMaxCost</b></a> ( int m )</div></li><li><div class=fn>virtual uint <a href="#count"><b>count</b></a> () const</div></li><li><div class=fn>uint <a href="#size"><b>size</b></a> () const</div></li><li><div class=fn>bool <a href="#isEmpty"><b>isEmpty</b></a> () const</div></li><li><div class=fn>virtual void <a href="#clear"><b>clear</b></a> ()</div></li><li><div class=fn>bool <a href="#insert"><b>insert</b></a> ( const QString & k, const type * d, int c = 1, int p = 0 )</div></li><li><div class=fn>bool <a href="#remove"><b>remove</b></a> ( const QString & k )</div></li><li><div class=fn>type * <a href="#take"><b>take</b></a> ( const QString & k )</div></li><li><div class=fn>type * <a href="#find"><b>find</b></a> ( const QString & k, bool ref = TRUE ) const</div></li><li><div class=fn>type * <a href="#operator[]"><b>operator[]</b></a> ( const QString & k ) const</div></li><li><div class=fn>void <a href="#statistics"><b>statistics</b></a> () const</div></li></ul><h2>Important Inherited Members</h2><ul><li><div class=fn>bool <a href="#autoDelete"><b>autoDelete</b></a> () const</div></li><li><div class=fn>void <a href="#setAutoDelete"><b>setAutoDelete</b></a> ( bool enable )</div></li></ul><hr><a name="details"></a><h2>Detailed Description</h2><p> The QCache class is a template class that provides a cache based on <a href="qstring.html">QString</a> keys.<p> <p> <p> A cache is a least recently used (LRU) list of cache items. Eachcache 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>(). Ifinserting a new item would cause the total cost to exceed themaximum cost, the least recently used items in the cache areremoved.<p> QCache is a template class. QCache<X> defines a cache thatoperates 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 useditem.<p> There are also methods to <a href="#remove">remove</a>() or <a href="#take">take</a>() an object from thecache. Calling <a href="qptrcollection.html#setAutoDelete">setAutoDelete</a>(TRUE) for a cache tells it to deleteitems that are removed. The default is to not delete items whenthey are removed (i.e., remove() and take() are equivalent).<p> When inserting an item into the cache, only the pointer is copied, notthe item itself. This is called a <a href="shclass.html#shallow-copy">shallow copy</a>. It is possible to make thecache copy all of the item's data (known as a <a href="shclass.html#deep-copy">deep copy</a>) when anitem is inserted. insert() calls the virtual function<a href="qptrcollection.html#newItem">QPtrCollection::newItem</a>() for the item to be inserted.Inherit a cache and reimplement it if you want deep copies.<p> When removing a cache item, the virtual function<a href="qptrcollection.html#deleteItem">QPtrCollection::deleteItem</a>() is called. The default implementationdeletes the item if auto-deletion is enabled, and does nothingotherwise.<p> There is a <a href="qcacheiterator.html">QCacheIterator</a> that can be used to traverse theitems in the cache in arbitrary order.<p> In QCache, the cache items are accessed via <a href="qstring.html">QString</a> keys, whichare Unicode strings. If you want to use non-Unicode, plain 8-bit <tt>char*</tt> keys, use the <a href="qasciicache.html">QAsciiCache</a> template. A QCache has the sameperformace as a QAsciiCache.<p> <p>See also <a href="qcacheiterator.html">QCacheIterator</a>, <a href="qasciicache.html">QAsciiCache</a>, <a href="qintcache.html">QIntCache</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="QCache-2"></a>QCache::QCache ( int maxCost = 100, int size = 17, bool caseSensitive = TRUE )</h3><p> Constructs a cache whose contents will never have a total costgreater 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 usuallybest to make it a prime number and at least 50% bigger than the largestexpected number of items in the cache.<p> Each inserted item has an associated cost. When inserting a newitem, if the total cost of all items in the cache will exceed <em>maxCost</em>, the cache will start throwing out the older (least recentlyused) items until there is enough room for the new item to beinserted.<p> If <em>caseSensitive</em> is TRUE (the default), the cache keys are casesensitive; if it is FALSE, they are case-insensitive.Case-insensitive comparison includes all letters in Unicode.<h3 class=fn><a name="~QCache"></a>QCache::~QCache ()</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>QPtrCollection::autoDelete () const</h3><p> Returns the setting of the auto-delete option. The default is FALSE.<p> <p>See also <a href="qptrcollection.html#setAutoDelete">setAutoDelete</a>().<h3 class=fn>void <a name="clear"></a>QCache::clear ()<tt> [virtual]</tt></h3><p> Removes all items from the cache and deletes them if auto-deletionhas 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="qptrcollection.html#clear">QPtrCollection</a>.<h3 class=fn>uint <a name="count"></a>QCache::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="qptrcollection.html#count">QPtrCollection</a>.<h3 class=fn>type * <a name="find"></a>QCache::find ( const <a href="qstring.html">QString</a> & k, bool ref = TRUE ) const</h3><p> Returns the item associated with key <em>k</em>, or null if the key does notexist in the cache. If <em>ref</em> is TRUE (the default), the item ismoved to the front of the least recently used list.<p> If there are two or more items with equal keys, the one thatwas inserted last is returned.<h3 class=fn>bool <a name="insert"></a>QCache::insert ( const <a href="qstring.html">QString</a> & k, const type * d, int c = 1, int p = 0 )</h3><p> Inserts the item <em>d</em> into the cache with key <em>k</em> and cost <em>c</em>. Returns TRUE if it is successful and FALSE if it fails.<p> The cache's size is limited, and if the total cost is too high,QCache will remove old, least recently used items until there is roomfor this new item.<p> The parameter <em>p</em> is internal and should be left at the defaultvalue (0).<p> <b>Warning:</b> If this function returns FALSE you must delete <em>d</em>yourself. Additionally, be very careful about using <em>d</em> aftercalling this function because any other insertions into the cache, fromanywhere in the application or within Qt itself, could cause theobject to be discarded from the cache and the pointer to becomeinvalid.<h3 class=fn>bool <a name="isEmpty"></a>QCache::isEmpty () const</h3><p> Returns TRUE if the cache is empty, or FALSE if there is at least oneobject in it.<h3 class=fn>int <a name="maxCost"></a>QCache::maxCost () const</h3><p> Returns the maximum allowed total cost of the cache.<p>See also <a href="#setMaxCost">setMaxCost</a>() and <a href="#totalCost">totalCost</a>().<h3 class=fn>type * <a name="operator[]"></a>QCache::operator[] ( const <a href="qstring.html">QString</a> & k ) const</h3><p> Returns the item associated with key <em>k</em>, or null if <em>k</em> does notexist in the cache, and moves the item to the front of the leastrecently used list.<p> If there are two or more items with equal keys, the one thatwas 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>QCache::remove ( const <a href="qstring.html">QString</a> & k )</h3><p> Removes the item associated with <em>k</em>, and returns TRUE if the itemwas present in the cache or FALSE if it was not.<p> The item is deleted if auto-deletion has been enabled, i.e., you havecalled <a href="qptrcollection.html#setAutoDelete">setAutoDelete</a>(TRUE).<p> If there are two or more items with equal keys, the one thatwas inserted last is removed.<p> All iterators that refer to the removed item are set to point to thenext 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>QPtrCollection::setAutoDelete ( bool enable )</h3><p> Sets the collection to auto-delete its contents if <em>enable</em> is TRUEand to never delete them if <em>enable</em> is FALSE.<p> If auto-deleting is turned on, all the items in a collection aredeleted when the collection itself is deleted. This is convenient ifthe collection has the only pointer to the items.<p> The default setting is FALSE, for safety. If you turn it on, becareful about copying the collection - you might find yourself withtwo collections deleting the same items.<p> Note that the auto-delete setting may also affect other functions insubclasses. For example, a subclass that has a <a href="#remove">remove</a>() functionwill remove the item from its data structure, and if auto-delete isenabled, will also delete the item.<p> <p>See also <a href="qptrcollection.html#autoDelete">autoDelete</a>().<p>Examples: <a href="grapher-nsplugin-example.html#x2777">grapher/grapher.cpp</a>, <a href="scribble-example.html#x945">scribble/scribble.cpp</a> and <a href="bigtable-example.html#x1489">table/bigtable/main.cpp</a>.<h3 class=fn>void <a name="setMaxCost"></a>QCache::setMaxCost ( int m )</h3><p> Sets the maximum allowed total cost of the cache to <em>m</em>. If thecurrent total cost is greater than <em>m</em>, some items are deletedimmediately.<p> <p>See also <a href="#maxCost">maxCost</a>() and <a href="#totalCost">totalCost</a>().<h3 class=fn>uint <a name="size"></a>QCache::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>QCache::statistics () const</h3><p> A debug-only utility function. Prints out cache usage, hit/miss, anddistribution information using <a href="qapplication.html#qDebug">qDebug</a>(). This function does nothingin the release library.<h3 class=fn>type * <a name="take"></a>QCache::take ( const <a href="qstring.html">QString</a> & k )</h3><p> Takes the item associated with <em>k</em> out of the cache withoutdeleting it and returns a pointer to the item taken out, or null ifthe key does not exist in the cache.<p> If there are two or more items with equal keys, the one thatwas inserted last is taken.<p> All iterators that refer to the taken item are set to point to thenext 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>QCache::totalCost () const</h3><p> Returns the total cost of the items in the cache. This is aninteger 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">Qt toolkit</a>.Copyright © 1995-2002<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 © 2002 <a href="http://www.trolltech.com">Trolltech</a><td><a href="http://www.trolltech.com/trademarks.html">Trademarks</a><td align=right><div align=right>Qt version 3.0.5</div></table></div></address></body></html>⌨️ 快捷键说明
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