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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/qasciicache.doc:41 --><html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>QAsciiCache 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>QAsciiCache Class Reference</h1><p>The QAsciiCache class is a template class that provides a cache based on char* keys.<a href="#details">More...</a><p><tt>#include <<a href="qasciicache-h.html">qasciicache.h</a>></tt><p><a href="qasciicache-members.html">List of all member functions.</a><h2>Public Members</h2><ul><li><div class=fn><a href="#QAsciiCache-2"><b>QAsciiCache</b></a> ( int maxCost = 100, int size = 17, bool caseSensitive = TRUE, bool copyKeys = TRUE )</div></li><li><div class=fn><a href="#~QAsciiCache"><b>~QAsciiCache</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 char * 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 char * k )</div></li><li><div class=fn>type * <a href="#take"><b>take</b></a> ( const char * k )</div></li><li><div class=fn>type * <a href="#find"><b>find</b></a> ( const char * k, bool ref = TRUE ) const</div></li><li><div class=fn>type * <a href="#operator[]"><b>operator[]</b></a> ( const char * k ) const</div></li><li><div class=fn>void <a href="#statistics"><b>statistics</b></a> () const</div></li></ul><hr><a name="details"></a><h2>Detailed Description</h2><p> The QAsciiCache class is a template class that provides a cache based on char* keys.<p> <p> QAsciiCache is implemented as a template class. Define a templateinstance QAsciiCache<X> to create a cache that operates on pointers toX (X*).<p> A cache is a least recently used (LRU) list of cache items. Thecache items are accessed via <tt>char*</tt> keys. For Unicode keys use the<a href="qcache.html">QCache</a> template instead, which uses <a href="qstring.html">QString</a> keys. A QCache hasthe same performace as a QAsciiCache.<p> Each cache item has a cost. The sum of item costs, <a href="#totalCost">totalCost</a>(), will notexceed the maximum cache cost, <a href="#maxCost">maxCost</a>(). If inserting a new itemwould cause the total cost to exceed the maximum cost, the leastrecently used items in the cache are removed.<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(TRUE)</a> tells the cache to deleteitems that are removed. The default is to not delete items whenthen 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. Its default implementationin QAsciiCache is to delete the item if <a href="qptrcollection.html#setAutoDelete">auto-deletion</a> is enabled.<p> There is a <a href="qasciicacheiterator.html">QAsciiCacheIterator</a> which may be used to traverse theitems in the cache in arbitrary order.<p> <p>See also <a href="qasciicacheiterator.html">QAsciiCacheIterator</a>, <a href="qcache.html">QCache</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="QAsciiCache-2"></a>QAsciiCache::QAsciiCache ( int maxCost = 100, int size = 17, bool caseSensitive = TRUE, bool copyKeys = 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 prime 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 (leastrecently used) 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 arecase-insensitive. Case-insensitive comparison includes only the 26letters in US-ASCII. If <em>copyKeys</em> is TRUE (the default),QAsciiCache makes a copy of the cache keys, otherwise it copies justthe const char * pointer - slightly faster if you can guarantee thatthe keys will never change, but very risky.<h3 class=fn><a name="~QAsciiCache"></a>QAsciiCache::~QAsciiCache ()</h3><p> Removes all items from the cache and destroys it.All iterators that access this cache will be reset.<h3 class=fn>void <a name="clear"></a>QAsciiCache::clear ()<tt> [virtual]</tt></h3><p> Removes all items from the cache, and deletes them if <a href="qptrcollection.html#setAutoDelete">auto-deletion</a> has been enabled.<p> All cache iterators that operate on this cache are reset.<p> <p>See also <a href="#remove">remove</a>() and <a href="#take">take</a>().<h3 class=fn>uint <a name="count"></a>QAsciiCache::count () const<tt> [virtual]</tt></h3><p> Returns the number of items in the cache.<p> <p>See also <a href="#totalCost">totalCost</a>() and <a href="#size">size</a>().<h3 class=fn>type * <a name="find"></a>QAsciiCache::find ( const char * k, bool ref = TRUE ) const</h3><p> Returns the item 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>QAsciiCache::insert ( const char * k, const type * d, int c = 1, int p = 0 )</h3><p> Inserts the item <em>d</em> into the cache using key <em>k</em>, and with a costof <em>c</em>. Returns TRUE if the item is successfully inserted.Returns FALSE if the item is not inserted, for example, if the costof the item exceeds <a href="#maxCost">maxCost</a>().<p> The cache's size is limited, and if the total cost is too high,QAsciiCache will remove old, least recently used items until there isroom for this new item.<p> Items with duplicate keys may be inserted.<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>QAsciiCache::isEmpty () const</h3><p> Returns TRUE if the cache is empty; otherwise returns FALSE.<h3 class=fn>int <a name="maxCost"></a>QAsciiCache::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>QAsciiCache::operator[] ( const char * k ) const</h3><p> Returns the item 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>QAsciiCache::remove ( const char * k )</h3><p> Removes the item with key <em>k</em> and returns TRUE if the itemwas present in the cache; otherwise returns FALSE.<p> The item is deleted if auto-deletion has been enabled, i.e., if youhave called <a href="qptrcollection.html#setAutoDelete">setAutoDelete(TRUE)</a>.<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="setMaxCost"></a>QAsciiCache::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 removedimmediately.<p> <p>See also <a href="#maxCost">maxCost</a>() and <a href="#totalCost">totalCost</a>().<h3 class=fn>uint <a name="size"></a>QAsciiCache::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>QAsciiCache::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>QAsciiCache::take ( const char * 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>QAsciiCache::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>. 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