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253 lines
13 KiB
253 lines
13 KiB
14 years ago
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/doc/qasciicache.doc:41 -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>QAsciiCache Class</title>
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<table border="0" cellpadding="0" cellspacing="0" width="100%">
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<tr bgcolor="#E5E5E5">
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<td valign=center>
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<a href="index.html">
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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<font color="#004faf">Main Classes</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>QAsciiCache Class Reference</h1>
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<p>The QAsciiCache class is a template class that provides a cache based on char* keys.
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<a href="#details">More...</a>
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<p><tt>#include <<a href="qasciicache-h.html">qasciicache.h</a>></tt>
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<p>Inherits <a href="qptrcollection.html">QPtrCollection</a>.
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<p><a href="qasciicache-members.html">List of all member functions.</a>
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<h2>Public Members</h2>
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<ul>
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<li class=fn><a href="#QAsciiCache-2"><b>QAsciiCache</b></a> ( int maxCost = 100, int size = 17, bool caseSensitive = TRUE, bool copyKeys = TRUE )</li>
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<li class=fn><a href="#~QAsciiCache"><b>~QAsciiCache</b></a> ()</li>
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<li class=fn>int <a href="#maxCost"><b>maxCost</b></a> () const</li>
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<li class=fn>int <a href="#totalCost"><b>totalCost</b></a> () const</li>
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<li class=fn>void <a href="#setMaxCost"><b>setMaxCost</b></a> ( int m )</li>
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<li class=fn>virtual uint <a href="#count"><b>count</b></a> () const</li>
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<li class=fn>uint <a href="#size"><b>size</b></a> () const</li>
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<li class=fn>bool <a href="#isEmpty"><b>isEmpty</b></a> () const</li>
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<li class=fn>virtual void <a href="#clear"><b>clear</b></a> ()</li>
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<li class=fn>bool <a href="#insert"><b>insert</b></a> ( const char * k, const type * d, int c = 1, int p = 0 )</li>
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<li class=fn>bool <a href="#remove"><b>remove</b></a> ( const char * k )</li>
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<li class=fn>type * <a href="#take"><b>take</b></a> ( const char * k )</li>
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<li class=fn>type * <a href="#find"><b>find</b></a> ( const char * k, bool ref = TRUE ) const</li>
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<li class=fn>type * <a href="#operator[]"><b>operator[]</b></a> ( const char * k ) const</li>
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<li class=fn>void <a href="#statistics"><b>statistics</b></a> () const</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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<p> The QAsciiCache class is a template class that provides a cache based on char* keys.
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<p>
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<p> QAsciiCache is implemented as a template class. Define a template
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instance QAsciiCache<X> to create a cache that operates on
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pointers to X (X*).
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<p> A cache is a least recently used (LRU) list of cache items. The
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cache items are accessed via <tt>char*</tt> keys. For Unicode keys use
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the <a href="qcache.html">QCache</a> template instead, which uses <a href="qstring.html">QString</a> keys. A QCache
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has the same performace as a QAsciiCache.
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<p> Each cache item has a cost. The sum of item costs, <a href="#totalCost">totalCost</a>(),
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will not exceed the maximum cache cost, <a href="#maxCost">maxCost</a>(). If inserting a
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new item would cause the total cost to exceed the maximum cost,
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the least recently used items in the cache are removed.
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<p> Apart from <a href="#insert">insert</a>(), by far the most important function is <a href="#find">find</a>()
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(which also exists as <a href="#operator[]">operator[]</a>()). This function looks up an
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item, returns it, and by default marks it as being the most
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recently used item.
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<p> There are also methods to <a href="#remove">remove</a>() or <a href="#take">take</a>() an object from the
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cache. Calling <a href="qptrcollection.html#setAutoDelete">setAutoDelete(TRUE)</a> tells the cache to delete items that
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are removed. The default is to not delete items when then are
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removed (i.e., remove() and take() are equivalent).
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<p> When inserting an item into the cache, only the pointer is copied,
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not the item itself. This is called a <a href="shclass.html#shallow-copy">shallow copy</a>. It is possible
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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
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function <a href="qptrcollection.html#newItem">QPtrCollection::newItem</a>() for the item to be inserted.
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Inherit a cache and reimplement <a href="qptrcollection.html#newItem">newItem</a>() if you want deep copies.
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<p> When removing a cache item the virtual function
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<a href="qptrcollection.html#deleteItem">QPtrCollection::deleteItem</a>() is called. Its default implementation
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in QAsciiCache is to delete the item if <a href="qptrcollection.html#setAutoDelete">auto-deletion</a> is enabled.
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<p> There is a <a href="qasciicacheiterator.html">QAsciiCacheIterator</a> which may be used to traverse the
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items in the cache in arbitrary order.
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<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>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn><a name="QAsciiCache-2"></a>QAsciiCache::QAsciiCache ( int maxCost = 100, int size = 17, bool caseSensitive = TRUE, bool copyKeys = TRUE )
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</h3>
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<p> Constructs a cache whose contents will never have a total cost
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greater than <em>maxCost</em> and which is expected to contain less than
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<em>size</em> items.
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<p> <em>size</em> is actually the size of an internal hash array; it's
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usually best to make it <a href="primes.html#prime">prime</a> and at least 50% bigger than the
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largest expected number of items in the cache.
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<p> Each inserted item has an associated cost. When inserting a new
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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
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recently used) items until there is enough room for the new item
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to be inserted.
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<p> If <em>caseSensitive</em> is TRUE (the default), the cache keys are case
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sensitive; if it is FALSE, they are case-insensitive.
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Case-insensitive comparison only affects the 26 letters in
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US-ASCII. If <em>copyKeys</em> is TRUE (the default), QAsciiCache makes
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a copy of the cache keys, otherwise it copies just the const char
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* pointer - slightly faster if you can guarantee that the keys
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will never change, but very risky.
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<h3 class=fn><a name="~QAsciiCache"></a>QAsciiCache::~QAsciiCache ()
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</h3>
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<p> Removes all items from the cache and destroys it.
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All iterators that access this cache will be reset.
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<h3 class=fn>void <a name="clear"></a>QAsciiCache::clear ()<tt> [virtual]</tt>
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</h3>
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<p> Removes all items from the cache, and deletes them if <a href="qptrcollection.html#setAutoDelete">auto-deletion</a> has been
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enabled.
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<p> All cache iterators that operate on this cache are reset.
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<p> <p>See also <a href="#remove">remove</a>() and <a href="#take">take</a>().
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<p>Reimplemented from <a href="qptrcollection.html#clear">QPtrCollection</a>.
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<h3 class=fn>uint <a name="count"></a>QAsciiCache::count () const<tt> [virtual]</tt>
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</h3>
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<p> Returns the number of items in the cache.
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<p> <p>See also <a href="#totalCost">totalCost</a>() and <a href="#size">size</a>().
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<p>Reimplemented from <a href="qptrcollection.html#count">QPtrCollection</a>.
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<h3 class=fn>type * <a name="find"></a>QAsciiCache::find ( const char * k, bool ref = TRUE ) const
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</h3>
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<p> Returns the item with key <em>k</em>, or 0 if the key does not exist
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in the cache. If <em>ref</em> is TRUE (the default), the item is moved
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to the front of the least recently used list.
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<p> If there are two or more items with equal keys, the one that was
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inserted last is returned.
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<h3 class=fn>bool <a name="insert"></a>QAsciiCache::insert ( const char * k, const type * d, int c = 1, int p = 0 )
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</h3>
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<p> Inserts the item <em>d</em> into the cache using key <em>k</em>, and with an
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associated cost of <em>c</em>. Returns TRUE if the item is successfully
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inserted. Returns FALSE if the item is not inserted, for example,
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if the cost of the item exceeds <a href="#maxCost">maxCost</a>().
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<p> The cache's size is limited, and if the total cost is too high,
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QAsciiCache will remove old, least recently used items until there
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is room for this new item.
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<p> Items with duplicate keys can be inserted.
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<p> The parameter <em>p</em> is internal and should be left at the default
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value (0).
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<p> <b>Warning:</b> If this function returns FALSE, you must delete <em>d</em>
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yourself. Additionally, be very careful about using <em>d</em> after
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calling this function, because any other insertions into the
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cache, from anywhere in the application or within Qt itself, could
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cause the object to be discarded from the cache and the pointer to
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become invalid.
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<h3 class=fn>bool <a name="isEmpty"></a>QAsciiCache::isEmpty () const
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</h3>
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<p> Returns TRUE if the cache is empty; otherwise returns FALSE.
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<h3 class=fn>int <a name="maxCost"></a>QAsciiCache::maxCost () const
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</h3>
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<p> Returns the maximum allowed total cost of the cache.
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<p> <p>See also <a href="#setMaxCost">setMaxCost</a>() and <a href="#totalCost">totalCost</a>().
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<h3 class=fn>type * <a name="operator[]"></a>QAsciiCache::operator[] ( const char * k ) const
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</h3>
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<p> Returns the item with key <em>k</em>, or 0 if <em>k</em> does not exist in
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the cache, and moves the item to the front of the least recently
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used list.
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<p> If there are two or more items with equal keys, the one that was
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inserted last is returned.
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<p> This is the same as <a href="#find">find</a>( k, TRUE ).
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<p> <p>See also <a href="#find">find</a>().
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<h3 class=fn>bool <a name="remove"></a>QAsciiCache::remove ( const char * k )
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</h3>
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<p> Removes the item with key <em>k</em> and returns TRUE if the item was
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present in the cache; otherwise returns FALSE.
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<p> The item is deleted if auto-deletion has been enabled, i.e., if
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you have called <a href="qptrcollection.html#setAutoDelete">setAutoDelete(TRUE)</a>.
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<p> If there are two or more items with equal keys, the one that was
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inserted last is removed.
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<p> All iterators that refer to the removed item are set to point to
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the next item in the cache's traversal order.
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<p> <p>See also <a href="#take">take</a>() and <a href="#clear">clear</a>().
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<h3 class=fn>void <a name="setMaxCost"></a>QAsciiCache::setMaxCost ( int m )
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</h3>
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<p> Sets the maximum allowed total cost of the cache to <em>m</em>. If the
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current total cost is greater than <em>m</em>, some items are removed
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immediately.
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<p> <p>See also <a href="#maxCost">maxCost</a>() and <a href="#totalCost">totalCost</a>().
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<h3 class=fn>uint <a name="size"></a>QAsciiCache::size () const
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</h3>
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<p> Returns the size of the hash array used to implement the cache.
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This should be a bit bigger than <a href="#count">count</a>() is likely to be.
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<h3 class=fn>void <a name="statistics"></a>QAsciiCache::statistics () const
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</h3>
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<p> A debug-only utility function. Prints out cache usage, hit/miss,
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and distribution information using <a href="qapplication.html#qDebug">qDebug</a>(). This function does
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nothing in the release library.
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<h3 class=fn>type * <a name="take"></a>QAsciiCache::take ( const char * k )
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</h3>
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<p> Takes the item associated with <em>k</em> out of the cache without
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deleting it and returns a pointer to the item taken out, or 0
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if the key does not exist in the cache.
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<p> If there are two or more items with equal keys, the one that was
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inserted last is taken.
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<p> All iterators that refer to the taken item are set to point to the
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next item in the cache's traversal order.
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<p> <p>See also <a href="#remove">remove</a>() and <a href="#clear">clear</a>().
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<h3 class=fn>int <a name="totalCost"></a>QAsciiCache::totalCost () const
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</h3>
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<p> Returns the total cost of the items in the cache. This is an
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integer in the range 0 to <a href="#maxCost">maxCost</a>().
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<p> <p>See also <a href="#setMaxCost">setMaxCost</a>().
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<!-- eof -->
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<hr><p>
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This file is part of the <a href="index.html">Qt toolkit</a>.
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Copyright © 1995-2007
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<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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</table></div></address></body>
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</html>
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