1QIntCache(3qt)                                                  QIntCache(3qt)
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NAME

6       QIntCache - Template class that provides a cache based on long keys
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SYNOPSIS

9       #include <qintcache.h>
10
11       Inherits QPtrCollection.
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13   Public Members
14       QIntCache ( int maxCost = 100, int size = 17 )
15       ~QIntCache ()
16       int maxCost () const
17       int totalCost () const
18       void setMaxCost ( int m )
19       virtual uint count () const
20       uint size () const
21       bool isEmpty () const
22       bool insert ( long k, const type * d, int c = 1, int p = 0 )
23       bool remove ( long k )
24       type * take ( long k )
25       virtual void clear ()
26       type * find ( long k, bool ref = TRUE ) const
27       type * operator[] ( long k ) const
28       void statistics () const
29

DESCRIPTION

31       The QIntCache class is a template class that provides a cache based on
32       long keys.
33
34       QIntCache is implemented as a template class. Define a template
35       instance QIntCache<X> to create a cache that operates on pointers to X,
36       or X*.
37
38       A cache is a least recently used (LRU) list of cache items, accessed
39       via long keys. Each cache item has a cost. The sum of item costs,
40       totalCost(), will not exceed the maximum cache cost, maxCost(). If
41       inserting a new item would cause the total cost to exceed the maximum
42       cost, the least recently used items in the cache are removed.
43
44       Apart from insert(), by far the most important function is find()
45       (which also exists as operator[]). This function looks up an item,
46       returns it, and by default marks it as being the most recently used
47       item.
48
49       There are also methods to remove() or take() an object from the cache.
50       Calling setAutoDelete(TRUE) for a cache tells it to delete items that
51       are removed. The default is to not delete items when they are removed
52       (i.e. remove() and take() are equivalent).
53
54       When inserting an item into the cache, only the pointer is copied, not
55       the item itself. This is called a shallow copy. It is possible to make
56       the cache copy all of the item's data (known as a deep copy) when an
57       item is inserted. insert() calls the virtual function
58       QPtrCollection::newItem() for the item to be inserted. Inherit a
59       dictionary and reimplement newItem() if you want deep copies.
60
61       When removing a cache item, the item will be automatically deleted if
62       auto-deletion is enabled.
63
64       There is a QIntCacheIterator which may be used to traverse the items in
65       the cache in arbitrary order.
66
67       See also QIntCacheIterator, QCache, QAsciiCache, Collection Classes,
68       and Non-GUI Classes.
69

MEMBER FUNCTION DOCUMENTATION

QIntCache::QIntCache ( int maxCost = 100, int size = 17 )

72       Constructs a cache whose contents will never have a total cost greater
73       than maxCost and which is expected to contain less than size items.
74
75       size is actually the size of an internal hash array; it's usually best
76       to make it prime and at least 50% bigger than the largest expected
77       number of items in the cache.
78
79       Each inserted item is associated with a cost. When inserting a new
80       item, if the total cost of all items in the cache will exceed maxCost,
81       the cache will start throwing out the older (least recently used) items
82       until there is enough room for the new item to be inserted.
83

QIntCache::~QIntCache ()

85       Removes all items from the cache and then destroys the int cache. If
86       auto-deletion is enabled the cache's items are deleted. All iterators
87       that access this cache will be reset.
88

void QIntCache::clear () [virtual]

90       Removes all items from the cache, and deletes them if auto-deletion has
91       been enabled.
92
93       All cache iterators that operate this on cache are reset.
94
95       See also remove() and take().
96
97       Reimplemented from QPtrCollection.
98

uint QIntCache::count () const [virtual]

100       Returns the number of items in the cache.
101
102       See also totalCost().
103
104       Reimplemented from QPtrCollection.
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type * QIntCache::find ( long k, bool ref = TRUE ) const

107       Returns the item associated with k, or 0 if the key does not exist in
108       the cache. If ref is TRUE (the default), the item is moved to the front
109       of the least recently used list.
110
111       If there are two or more items with equal keys, the one that was
112       inserted most recently is returned.
113

bool QIntCache::insert ( long k, const type * d, int c = 1, int p = 0 )

115       Inserts the item d into the cache with key k and assigns it a cost of c
116       (default 1). Returns TRUE if it succeeds; otherwise returns FALSE.
117
118       The cache's size is limited, and if the total cost is too high,
119       QIntCache will remove old, least-used items until there is room for
120       this new item.
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122       The parameter p is internal and should be left at the default value
123       (0).
124
125       Warning: If this function returns FALSE (for example, the cost ,
126       exceeds maxCost()), you must delete d yourself. Additionally, be very
127       careful about using d after calling this function. Any other insertions
128       into the cache, from anywhere in the application or within Qt itself,
129       could cause the object to be discarded from the cache and the pointer
130       to become invalid.
131

bool QIntCache::isEmpty () const

133       Returns TRUE if the cache is empty; otherwise returns FALSE.
134

int QIntCache::maxCost () const

136       Returns the maximum allowed total cost of the cache.
137
138       See also setMaxCost() and totalCost().
139

type * QIntCache::operator[] ( long k ) const

141       Returns the item associated with k, or 0 if k does not exist in the
142       cache, and moves the item to the front of the least recently used list.
143
144       If there are two or more items with equal keys, the one that was
145       inserted most recently is returned.
146
147       This is the same as find( k, TRUE ).
148
149       See also find().
150

bool QIntCache::remove ( long k )

152       Removes the item associated with k, and returns TRUE if the item was
153       present in the cache; otherwise returns FALSE.
154
155       The item is deleted if auto-deletion has been enabled, i.e. if you have
156       called setAutoDelete(TRUE).
157
158       If there are two or more items with equal keys, the one that was
159       inserted most recently is removed.
160
161       All iterators that refer to the removed item are set to point to the
162       next item in the cache's traversal order.
163
164       See also take() and clear().
165

void QIntCache::setMaxCost ( int m )

167       Sets the maximum allowed total cost of the cache to m. If the current
168       total cost is greater than m, some items are removed immediately.
169
170       See also maxCost() and totalCost().
171

uint QIntCache::size () const

173       Returns the size of the hash array used to implement the cache. This
174       should be a bit larger than count() is likely to be.
175

void QIntCache::statistics () const

177       A debug-only utility function. Prints out cache usage, hit/miss, and
178       distribution information using qDebug(). This function does nothing in
179       the release library.
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type * QIntCache::take ( long k )

182       Takes the item associated with k out of the cache without deleting it,
183       and returns a pointer to the item taken out or 0 if the key does not
184       exist in the cache.
185
186       If there are two or more items with equal keys, the one that was
187       inserted most recently is taken.
188
189       All iterators that refer to the taken item are set to point to the next
190       item in the cache's traversal order.
191
192       See also remove() and clear().
193

int QIntCache::totalCost () const

195       Returns the total cost of the items in the cache. This is an integer in
196       the range 0 to maxCost().
197
198       See also setMaxCost().
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200

SEE ALSO

202       http://doc.trolltech.com/qintcache.html
203       http://www.trolltech.com/faq/tech.html
204
206       Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com.  See the
207       license file included in the distribution for a complete license
208       statement.
209

AUTHOR

211       Generated automatically from the source code.
212

BUGS

214       If you find a bug in Qt, please report it as described in
215       http://doc.trolltech.com/bughowto.html.  Good bug reports help us to
216       help you. Thank you.
217
218       The definitive Qt documentation is provided in HTML format; it is
219       located at $QTDIR/doc/html and can be read using Qt Assistant or with a
220       web browser. This man page is provided as a convenience for those users
221       who prefer man pages, although this format is not officially supported
222       by Trolltech.
223
224       If you find errors in this manual page, please report them to qt-
225       bugs@trolltech.com.  Please include the name of the manual page
226       (qintcache.3qt) and the Qt version (3.3.8).
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230Trolltech AS                    2 February 2007                 QIntCache(3qt)
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