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243 lines
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<title>QIntCache Class</title>
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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>QIntCache Class Reference</h1>
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<p>The QIntCache class is a template class that provides a cache based on long keys.
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<a href="#details">More...</a>
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<p><tt>#include <<a href="qintcache-h.html">qintcache.h</a>></tt>
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<p>Inherits <a href="qptrcollection.html">QPtrCollection</a>.
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<p><a href="qintcache-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="#QIntCache-2"><b>QIntCache</b></a> ( int maxCost = 100, int size = 17 )</li>
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<li class=fn><a href="#~QIntCache"><b>~QIntCache</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>bool <a href="#insert"><b>insert</b></a> ( long 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> ( long k )</li>
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<li class=fn>type * <a href="#take"><b>take</b></a> ( long k )</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>type * <a href="#find"><b>find</b></a> ( long k, bool ref = TRUE ) const</li>
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<li class=fn>type * <a href="#operator[]"><b>operator[]</b></a> ( long 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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The QIntCache class is a template class that provides a cache based on long keys.
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<p>
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<p> QIntCache is implemented as a template class. Define a template
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instance QIntCache<X> to create a cache that operates on
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pointers to X, or X*.
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<p> A cache is a least recently used (LRU) list of cache items,
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accessed via <tt>long</tt> keys. Each cache item has a cost. The sum
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of item costs, <a href="#totalCost">totalCost</a>(), will not exceed the maximum cache
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cost, <a href="#maxCost">maxCost</a>(). If inserting a new item would cause the total
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cost to exceed the maximum cost, the least recently used items in
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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 operator[]). 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</a>(TRUE) for a cache tells it to delete
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items that are removed. The default is to not delete items when
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they are 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 dictionary and reimplement <a href="qptrcollection.html#newItem">newItem</a>() if you want deep
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copies.
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<p> When removing a cache item, the item will be automatically
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deleted if auto-deletion is enabled.
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<p> There is a <a href="qintcacheiterator.html">QIntCacheIterator</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="qintcacheiterator.html">QIntCacheIterator</a>, <a href="qcache.html">QCache</a>, <a href="qasciicache.html">QAsciiCache</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="QIntCache-2"></a>QIntCache::QIntCache ( int maxCost = 100, int size = 17 )
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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 is associated with a 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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<h3 class=fn><a name="~QIntCache"></a>QIntCache::~QIntCache ()
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</h3>
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<p> Removes all items from the cache and then destroys the int cache.
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If auto-deletion is enabled the cache's items are deleted. All
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iterators that access this cache will be reset.
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<h3 class=fn>void <a name="clear"></a>QIntCache::clear ()<tt> [virtual]</tt>
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</h3>
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<p> Removes all items from the cache, and deletes them if
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auto-deletion has been enabled.
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<p> All cache iterators that operate this on 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>QIntCache::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>().
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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>QIntCache::find ( long k, bool ref = TRUE ) const
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</h3>
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<p> Returns the item associated with <em>k</em>, or 0 if the key does not
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exist in the cache. If <em>ref</em> is TRUE (the default), the item is
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moved 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 most recently is returned.
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<h3 class=fn>bool <a name="insert"></a>QIntCache::insert ( long 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 with key <em>k</em> and assigns it
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a cost of <em>c</em> (default 1). Returns TRUE if it succeeds; otherwise
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returns FALSE.
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<p> The cache's size is limited, and if the total cost is too high,
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QIntCache will remove old, least-used items until there is room
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for this new item.
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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 (for example, the cost <tt>,</tt>
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exceeds <a href="#maxCost">maxCost</a>()), you must delete <em>d</em> yourself. Additionally,
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be very careful about using <em>d</em> after calling this function. Any
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other insertions into the cache, from anywhere in the application
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or within Qt itself, could cause the object to be discarded from
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the cache and the pointer to become invalid.
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<h3 class=fn>bool <a name="isEmpty"></a>QIntCache::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>QIntCache::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>QIntCache::operator[] ( long k ) const
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</h3>
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<p> Returns the item associated with <em>k</em>, or 0 if <em>k</em> does not exist
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in the cache, and moves the item to the front of the least
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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 most recently 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>QIntCache::remove ( long k )
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</h3>
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<p> Removes the item associated with <em>k</em>, and returns TRUE if the
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item was 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 you
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have called <a href="qptrcollection.html#setAutoDelete">setAutoDelete</a>(TRUE).
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<p> If there are two or more items with equal keys, the one that was
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inserted most recently 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>QIntCache::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>QIntCache::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 larger than <a href="#count">count</a>() is likely to be.
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<h3 class=fn>void <a name="statistics"></a>QIntCache::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>QIntCache::take ( long 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 if
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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 most recently 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>QIntCache::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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