/
qhash.cpp
1914 lines (1387 loc) · 52.6 KB
/
qhash.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see http://www.qt.io/terms-conditions. For further
** information use the contact form at http://www.qt.io/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 or version 3 as published by the Free
** Software Foundation and appearing in the file LICENSE.LGPLv21 and
** LICENSE.LGPLv3 included in the packaging of this file. Please review the
** following information to ensure the GNU Lesser General Public License
** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** As a special exception, The Qt Company gives you certain additional
** rights. These rights are described in The Qt Company LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include "qhash.h"
#ifdef truncate
#undef truncate
#endif
#include <qbitarray.h>
#include <qstring.h>
#include <stdlib.h>
#ifdef QT_QHASH_DEBUG
#include <qstring.h>
#endif
QT_BEGIN_NAMESPACE
// ### Qt 5: see tests/benchmarks/corelib/tools/qhash/qhash_string.cpp
// Hashing of the whole string is a waste of cycles.
/*
These functions are based on Peter J. Weinberger's hash function
(from the Dragon Book). The constant 24 in the original function
was replaced with 23 to produce fewer collisions on input such as
"a", "aa", "aaa", "aaaa", ...
*/
static uint hash(const uchar *p, int n)
{
uint h = 0;
while (n--) {
h = (h << 4) + *p++;
h ^= (h & 0xf0000000) >> 23;
h &= 0x0fffffff;
}
return h;
}
static uint hash(const QChar *p, int n)
{
uint h = 0;
while (n--) {
h = (h << 4) + (*p++).unicode();
h ^= (h & 0xf0000000) >> 23;
h &= 0x0fffffff;
}
return h;
}
uint qHash(const QByteArray &key)
{
return hash(reinterpret_cast<const uchar *>(key.constData()), key.size());
}
uint qHash(const QString &key)
{
return hash(key.unicode(), key.size());
}
uint qHash(const QStringRef &key)
{
return hash(key.unicode(), key.size());
}
uint qHash(const QBitArray &bitArray)
{
int m = bitArray.d.size() - 1;
uint result = hash(reinterpret_cast<const uchar *>(bitArray.d.constData()), qMax(0, m));
// deal with the last 0 to 7 bits manually, because we can't trust that
// the padding is initialized to 0 in bitArray.d
int n = bitArray.size();
if (n & 0x7)
result = ((result << 4) + bitArray.d.at(m)) & ((1 << n) - 1);
return result;
}
/*
The prime_deltas array is a table of selected prime values, even
though it doesn't look like one. The primes we are using are 1,
2, 5, 11, 17, 37, 67, 131, 257, ..., i.e. primes in the immediate
surrounding of a power of two.
The primeForNumBits() function returns the prime associated to a
power of two. For example, primeForNumBits(8) returns 257.
*/
static const uchar prime_deltas[] = {
0, 0, 1, 3, 1, 5, 3, 3, 1, 9, 7, 5, 3, 9, 25, 3,
1, 21, 3, 21, 7, 15, 9, 5, 3, 29, 15, 0, 0, 0, 0, 0
};
static inline int primeForNumBits(int numBits)
{
return (1 << numBits) + prime_deltas[numBits];
}
/*
Returns the smallest integer n such that
primeForNumBits(n) >= hint.
*/
static int countBits(int hint)
{
int numBits = 0;
int bits = hint;
while (bits > 1) {
bits >>= 1;
numBits++;
}
if (numBits >= (int)sizeof(prime_deltas)) {
numBits = sizeof(prime_deltas) - 1;
} else if (primeForNumBits(numBits) < hint) {
++numBits;
}
return numBits;
}
/*
A QHash has initially around pow(2, MinNumBits) buckets. For
example, if MinNumBits is 4, it has 17 buckets.
*/
const int MinNumBits = 4;
QHashData QHashData::shared_null = {
0, 0, Q_BASIC_ATOMIC_INITIALIZER(1), 0, 0, MinNumBits, 0, 0, true, false, 0
};
void *QHashData::allocateNode()
{
return allocateNode(0);
}
void *QHashData::allocateNode(int nodeAlign)
{
void *ptr = strictAlignment ? qMallocAligned(nodeSize, nodeAlign) : qMalloc(nodeSize);
Q_CHECK_PTR(ptr);
return ptr;
}
void QHashData::freeNode(void *node)
{
if (strictAlignment)
qFreeAligned(node);
else
qFree(node);
}
QHashData *QHashData::detach_helper(void (*node_duplicate)(Node *, void *), int nodeSize)
{
return detach_helper2( node_duplicate, 0, nodeSize, 0 );
}
QHashData *QHashData::detach_helper2(void (*node_duplicate)(Node *, void *),
void (*node_delete)(Node *),
int nodeSize,
int nodeAlign)
{
union {
QHashData *d;
Node *e;
};
d = new QHashData;
d->fakeNext = 0;
d->buckets = 0;
d->ref = 1;
d->size = size;
d->nodeSize = nodeSize;
d->userNumBits = userNumBits;
d->numBits = numBits;
d->numBuckets = numBuckets;
d->sharable = true;
d->strictAlignment = nodeAlign > 8;
d->reserved = 0;
if (numBuckets) {
QT_TRY {
d->buckets = new Node *[numBuckets];
} QT_CATCH(...) {
// restore a consistent state for d
d->numBuckets = 0;
// roll back
d->free_helper(node_delete);
QT_RETHROW;
}
Node *this_e = reinterpret_cast<Node *>(this);
for (int i = 0; i < numBuckets; ++i) {
Node **nextNode = &d->buckets[i];
Node *oldNode = buckets[i];
while (oldNode != this_e) {
QT_TRY {
Node *dup = static_cast<Node *>(allocateNode(nodeAlign));
QT_TRY {
node_duplicate(oldNode, dup);
} QT_CATCH(...) {
freeNode( dup );
QT_RETHROW;
}
dup->h = oldNode->h;
*nextNode = dup;
nextNode = &dup->next;
oldNode = oldNode->next;
} QT_CATCH(...) {
// restore a consistent state for d
*nextNode = e;
d->numBuckets = i+1;
// roll back
d->free_helper(node_delete);
QT_RETHROW;
}
}
*nextNode = e;
}
}
return d;
}
void QHashData::free_helper(void (*node_delete)(Node *))
{
if (node_delete) {
Node *this_e = reinterpret_cast<Node *>(this);
Node **bucket = reinterpret_cast<Node **>(this->buckets);
int n = numBuckets;
while (n--) {
Node *cur = *bucket++;
while (cur != this_e) {
Node *next = cur->next;
node_delete(cur);
freeNode(cur);
cur = next;
}
}
}
delete [] buckets;
delete this;
}
QHashData::Node *QHashData::nextNode(Node *node)
{
union {
Node *next;
Node *e;
QHashData *d;
};
next = node->next;
Q_ASSERT_X(next, "QHash", "Iterating beyond end()");
if (next->next)
return next;
int start = (node->h % d->numBuckets) + 1;
Node **bucket = d->buckets + start;
int n = d->numBuckets - start;
while (n--) {
if (*bucket != e)
return *bucket;
++bucket;
}
return e;
}
QHashData::Node *QHashData::previousNode(Node *node)
{
union {
Node *e;
QHashData *d;
};
e = node;
while (e->next)
e = e->next;
int start;
if (node == e)
start = d->numBuckets - 1;
else
start = node->h % d->numBuckets;
Node *sentinel = node;
Node **bucket = d->buckets + start;
while (start >= 0) {
if (*bucket != sentinel) {
Node *prev = *bucket;
while (prev->next != sentinel)
prev = prev->next;
return prev;
}
sentinel = e;
--bucket;
--start;
}
Q_ASSERT_X(start >= 0, "QHash", "Iterating backward beyond begin()");
return e;
}
/*
If hint is negative, -hint gives the approximate number of
buckets that should be used for the hash table. If hint is
nonnegative, (1 << hint) gives the approximate number
of buckets that should be used.
*/
void QHashData::rehash(int hint)
{
if (hint < 0) {
hint = countBits(-hint);
if (hint < MinNumBits)
hint = MinNumBits;
userNumBits = hint;
while (primeForNumBits(hint) < (size >> 1))
++hint;
} else if (hint < MinNumBits) {
hint = MinNumBits;
}
if (numBits != hint) {
Node *e = reinterpret_cast<Node *>(this);
Node **oldBuckets = buckets;
int oldNumBuckets = numBuckets;
int nb = primeForNumBits(hint);
buckets = new Node *[nb];
numBits = hint;
numBuckets = nb;
for (int i = 0; i < numBuckets; ++i)
buckets[i] = e;
for (int i = 0; i < oldNumBuckets; ++i) {
Node *firstNode = oldBuckets[i];
while (firstNode != e) {
uint h = firstNode->h;
Node *lastNode = firstNode;
while (lastNode->next != e && lastNode->next->h == h)
lastNode = lastNode->next;
Node *afterLastNode = lastNode->next;
Node **beforeFirstNode = &buckets[h % numBuckets];
while (*beforeFirstNode != e)
beforeFirstNode = &(*beforeFirstNode)->next;
lastNode->next = *beforeFirstNode;
*beforeFirstNode = firstNode;
firstNode = afterLastNode;
}
}
delete [] oldBuckets;
}
}
void QHashData::destroyAndFree()
{
free_helper(0);
}
#ifdef QT_QHASH_DEBUG
void QHashData::dump()
{
qDebug("Hash data (ref = %d, size = %d, nodeSize = %d, userNumBits = %d, numBits = %d, numBuckets = %d)",
int(ref), size, nodeSize, userNumBits, numBits,
numBuckets);
qDebug(" %p (fakeNode = %p)", this, fakeNext);
for (int i = 0; i < numBuckets; ++i) {
QString line;
Node *n = buckets[i];
if (n != reinterpret_cast<Node *>(this)) {
line.sprintf("%d:", i);
while (n != reinterpret_cast<Node *>(this)) {
line += QString().sprintf(" -> [%p]", n);
if (!n) {
line += " (CORRUPT)";
break;
}
n = n->next;
}
qDebug(qPrintable(line));
}
}
}
void QHashData::checkSanity()
{
if (fakeNext)
qFatal("Fake next isn't 0");
for (int i = 0; i < numBuckets; ++i) {
Node *n = buckets[i];
Node *p = n;
if (!n)
qFatal("%d: Bucket entry is 0", i);
if (n != reinterpret_cast<Node *>(this)) {
while (n != reinterpret_cast<Node *>(this)) {
if (!n->next)
qFatal("%d: Next of %p is 0, should be %p", i, n, this);
n = n->next;
}
}
}
}
#endif
/*!
\fn uint qHash(const QPair<T1, T2> &key)
\since 4.3
\relates QHash
Returns the hash value for the \a key.
Types \c T1 and \c T2 must be supported by qHash().
*/
/*! \fn uint qHash(char key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(uchar key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(signed char key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(ushort key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(short key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(uint key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(int key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(ulong key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(long key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(quint64 key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(qint64 key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(QChar key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(const QByteArray &key)
\fn uint qHash(const QBitArray &key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(const QString &key)
\relates QHash
Returns the hash value for the \a key.
*/
/*! \fn uint qHash(const T *key)
\relates QHash
Returns the hash value for the \a key.
*/
/*!
\class QHash
\brief The QHash class is a template class that provides a hash-table-based dictionary.
\ingroup tools
\ingroup shared
\reentrant
QHash\<Key, T\> is one of Qt's generic \l{container classes}. It
stores (key, value) pairs and provides very fast lookup of the
value associated with a key.
QHash provides very similar functionality to QMap. The
differences are:
\list
\i QHash provides faster lookups than QMap. (See \l{Algorithmic
Complexity} for details.)
\i When iterating over a QMap, the items are always sorted by
key. With QHash, the items are arbitrarily ordered.
\i The key type of a QMap must provide operator<(). The key
type of a QHash must provide operator==() and a global
hash function called qHash() (see the related non-member
functions).
\endlist
Here's an example QHash with QString keys and \c int values:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 0
To insert a (key, value) pair into the hash, you can use operator[]():
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 1
This inserts the following three (key, value) pairs into the
QHash: ("one", 1), ("three", 3), and ("seven", 7). Another way to
insert items into the hash is to use insert():
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 2
To look up a value, use operator[]() or value():
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 3
If there is no item with the specified key in the hash, these
functions return a \l{default-constructed value}.
If you want to check whether the hash contains a particular key,
use contains():
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 4
There is also a value() overload that uses its second argument as
a default value if there is no item with the specified key:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 5
In general, we recommend that you use contains() and value()
rather than operator[]() for looking up a key in a hash. The
reason is that operator[]() silently inserts an item into the
hash if no item exists with the same key (unless the hash is
const). For example, the following code snippet will create 1000
items in memory:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 6
To avoid this problem, replace \c hash[i] with \c hash.value(i)
in the code above.
If you want to navigate through all the (key, value) pairs stored
in a QHash, you can use an iterator. QHash provides both
\l{Java-style iterators} (QHashIterator and QMutableHashIterator)
and \l{STL-style iterators} (QHash::const_iterator and
QHash::iterator). Here's how to iterate over a QHash<QString,
int> using a Java-style iterator:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 7
Here's the same code, but using an STL-style iterator:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 8
QHash is unordered, so an iterator's sequence cannot be assumed
to be predictable. If ordering by key is required, use a QMap.
Normally, a QHash allows only one value per key. If you call
insert() with a key that already exists in the QHash, the
previous value is erased. For example:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 9
However, you can store multiple values per key by using
insertMulti() instead of insert() (or using the convenience
subclass QMultiHash). If you want to retrieve all
the values for a single key, you can use values(const Key &key),
which returns a QList<T>:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 10
The items that share the same key are available from most
recently to least recently inserted. A more efficient approach is
to call find() to get the iterator for the first item with a key
and iterate from there:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 11
If you only need to extract the values from a hash (not the keys),
you can also use \l{foreach}:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 12
Items can be removed from the hash in several ways. One way is to
call remove(); this will remove any item with the given key.
Another way is to use QMutableHashIterator::remove(). In addition,
you can clear the entire hash using clear().
QHash's key and value data types must be \l{assignable data
types}. You cannot, for example, store a QWidget as a value;
instead, store a QWidget *. In addition, QHash's key type must
provide operator==(), and there must also be a global qHash()
function that returns a hash value for an argument of the key's
type.
Here's a list of the C++ and Qt types that can serve as keys in a
QHash: any integer type (char, unsigned long, etc.), any pointer
type, QChar, QString, and QByteArray. For all of these, the \c
<QHash> header defines a qHash() function that computes an
adequate hash value. If you want to use other types as the key,
make sure that you provide operator==() and a qHash()
implementation.
Example:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 13
The qHash() function computes a numeric value based on a key. It
can use any algorithm imaginable, as long as it always returns
the same value if given the same argument. In other words, if
\c{e1 == e2}, then \c{qHash(e1) == qHash(e2)} must hold as well.
However, to obtain good performance, the qHash() function should
attempt to return different hash values for different keys to the
largest extent possible.
In the example above, we've relied on Qt's global qHash(const
QString &) to give us a hash value for the employee's name, and
XOR'ed this with the day they were born to help produce unique
hashes for people with the same name.
Internally, QHash uses a hash table to perform lookups. Unlike Qt
3's \c QDict class, which needed to be initialized with a prime
number, QHash's hash table automatically grows and shrinks to
provide fast lookups without wasting too much memory. You can
still control the size of the hash table by calling reserve() if
you already know approximately how many items the QHash will
contain, but this isn't necessary to obtain good performance. You
can also call capacity() to retrieve the hash table's size.
\sa QHashIterator, QMutableHashIterator, QMap, QSet
*/
/*! \fn QHash::QHash()
Constructs an empty hash.
\sa clear()
*/
/*! \fn QHash::QHash(const QHash<Key, T> &other)
Constructs a copy of \a other.
This operation occurs in \l{constant time}, because QHash is
\l{implicitly shared}. This makes returning a QHash from a
function very fast. If a shared instance is modified, it will be
copied (copy-on-write), and this takes \l{linear time}.
\sa operator=()
*/
/*! \fn QHash::~QHash()
Destroys the hash. References to the values in the hash and all
iterators of this hash become invalid.
*/
/*! \fn QHash<Key, T> &QHash::operator=(const QHash<Key, T> &other)
Assigns \a other to this hash and returns a reference to this hash.
*/
/*! \fn void QHash::swap(QHash<Key, T> &other)
\since 4.8
Swaps hash \a other with this hash. This operation is very
fast and never fails.
*/
/*! \fn void QMultiHash::swap(QMultiHash<Key, T> &other)
\since 4.8
Swaps hash \a other with this hash. This operation is very
fast and never fails.
*/
/*! \fn bool QHash::operator==(const QHash<Key, T> &other) const
Returns true if \a other is equal to this hash; otherwise returns
false.
Two hashes are considered equal if they contain the same (key,
value) pairs.
This function requires the value type to implement \c operator==().
\sa operator!=()
*/
/*! \fn bool QHash::operator!=(const QHash<Key, T> &other) const
Returns true if \a other is not equal to this hash; otherwise
returns false.
Two hashes are considered equal if they contain the same (key,
value) pairs.
This function requires the value type to implement \c operator==().
\sa operator==()
*/
/*! \fn int QHash::size() const
Returns the number of items in the hash.
\sa isEmpty(), count()
*/
/*! \fn bool QHash::isEmpty() const
Returns true if the hash contains no items; otherwise returns
false.
\sa size()
*/
/*! \fn int QHash::capacity() const
Returns the number of buckets in the QHash's internal hash table.
The sole purpose of this function is to provide a means of fine
tuning QHash's memory usage. In general, you will rarely ever
need to call this function. If you want to know how many items are
in the hash, call size().
\sa reserve(), squeeze()
*/
/*! \fn void QHash::reserve(int size)
Ensures that the QHash's internal hash table consists of at least
\a size buckets.
This function is useful for code that needs to build a huge hash
and wants to avoid repeated reallocation. For example:
\snippet doc/src/snippets/code/src_corelib_tools_qhash.cpp 14
Ideally, \a size should be slightly more than the maximum number
of items expected in the hash. \a size doesn't have to be prime,
because QHash will use a prime number internally anyway. If \a size
is an underestimate, the worst that will happen is that the QHash
will be a bit slower.
In general, you will rarely ever need to call this function.
QHash's internal hash table automatically shrinks or grows to
provide good performance without wasting too much memory.
\sa squeeze(), capacity()
*/
/*! \fn void QHash::squeeze()
Reduces the size of the QHash's internal hash table to save
memory.
The sole purpose of this function is to provide a means of fine
tuning QHash's memory usage. In general, you will rarely ever
need to call this function.
\sa reserve(), capacity()
*/
/*! \fn void QHash::detach()
\internal
Detaches this hash from any other hashes with which it may share
data.
\sa isDetached()
*/
/*! \fn bool QHash::isDetached() const
\internal
Returns true if the hash's internal data isn't shared with any
other hash object; otherwise returns false.
\sa detach()
*/
/*! \fn void QHash::setSharable(bool sharable)
\internal
*/
/*! \fn bool QHash::isSharedWith(const QHash<Key, T> &other) const
\internal
*/
/*! \fn void QHash::clear()
Removes all items from the hash.
\sa remove()
*/
/*! \fn int QHash::remove(const Key &key)
Removes all the items that have the \a key from the hash.
Returns the number of items removed which is usually 1 but will
be 0 if the key isn't in the hash, or greater than 1 if
insertMulti() has been used with the \a key.
\sa clear(), take(), QMultiHash::remove()
*/
/*! \fn T QHash::take(const Key &key)
Removes the item with the \a key from the hash and returns
the value associated with it.
If the item does not exist in the hash, the function simply
returns a \l{default-constructed value}. If there are multiple
items for \a key in the hash, only the most recently inserted one
is removed.
If you don't use the return value, remove() is more efficient.
\sa remove()
*/
/*! \fn bool QHash::contains(const Key &key) const
Returns true if the hash contains an item with the \a key;
otherwise returns false.
\sa count(), QMultiHash::contains()
*/
/*! \fn const T QHash::value(const Key &key) const
Returns the value associated with the \a key.
If the hash contains no item with the \a key, the function
returns a \l{default-constructed value}. If there are multiple
items for the \a key in the hash, the value of the most recently
inserted one is returned.
\sa key(), values(), contains(), operator[]()
*/
/*! \fn const T QHash::value(const Key &key, const T &defaultValue) const
\overload
If the hash contains no item with the given \a key, the function returns
\a defaultValue.
*/
/*! \fn T &QHash::operator[](const Key &key)
Returns the value associated with the \a key as a modifiable
reference.
If the hash contains no item with the \a key, the function inserts
a \l{default-constructed value} into the hash with the \a key, and
returns a reference to it. If the hash contains multiple items
with the \a key, this function returns a reference to the most
recently inserted value.
\sa insert(), value()
*/
/*! \fn const T QHash::operator[](const Key &key) const
\overload
Same as value().
*/
/*! \fn QList<Key> QHash::uniqueKeys() const
\since 4.2
Returns a list containing all the keys in the map. Keys that occur multiple
times in the map (because items were inserted with insertMulti(), or
unite() was used) occur only once in the returned list.
\sa keys(), values()
*/
/*! \fn QList<Key> QHash::keys() const
Returns a list containing all the keys in the hash, in an
arbitrary order. Keys that occur multiple times in the hash
(because items were inserted with insertMulti(), or unite() was
used) also occur multiple times in the list.
To obtain a list of unique keys, where each key from the map only
occurs once, use uniqueKeys().
The order is guaranteed to be the same as that used by values().
\sa uniqueKeys(), values(), key()
*/
/*! \fn QList<Key> QHash::keys(const T &value) const
\overload
Returns a list containing all the keys associated with value \a
value, in an arbitrary order.
This function can be slow (\l{linear time}), because QHash's
internal data structure is optimized for fast lookup by key, not
by value.
*/
/*! \fn QList<T> QHash::values() const
Returns a list containing all the values in the hash, in an
arbitrary order. If a key is associated multiple values, all of
its values will be in the list, and not just the most recently
inserted one.
The order is guaranteed to be the same as that used by keys().
\sa keys(), value()
*/
/*! \fn QList<T> QHash::values(const Key &key) const
\overload