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
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 22. Policy-Based Data Structures</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.77.1" /><meta name="keywords" content="ISO C++, policy, container, data, structure, associated, tree, trie, hash, metaprogramming" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="extensions.html" title="Part III. Extensions" /><link rel="prev" href="bitmap_allocator_impl.html" title="Implementation" /><link rel="next" href="policy_data_structures_using.html" title="Using" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 22. Policy-Based Data Structures</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bitmap_allocator_impl.html">Prev</a> </td><th width="60%" align="center">Part III.
Extensions
</th><td width="20%" align="right"> <a accesskey="n" href="policy_data_structures_using.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.containers.pbds"></a>Chapter 22. Policy-Based Data Structures</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="section"><a href="policy_data_structures.html#pbds.intro">Intro</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures.html#pbds.intro.issues">Performance Issues</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures.html#pbds.intro.issues.associative">Associative</a></span></dt><dt><span class="section"><a href="policy_data_structures.html#pbds.intro.issues.priority_queue">Priority Que</a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures.html#pbds.intro.motivation">Goals</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures.html#pbds.intro.motivation.associative">Associative</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures.html#motivation.associative.policy">Policy Choices</a></span></dt><dt><span class="section"><a href="policy_data_structures.html#motivation.associative.underlying">Underlying Data Structures</a></span></dt><dt><span class="section"><a href="policy_data_structures.html#motivation.associative.iterators">Iterators</a></span></dt><dt><span class="section"><a href="policy_data_structures.html#motivation.associative.functions">Functional</a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures.html#pbds.intro.motivation.priority_queue">Priority Queues</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures.html#motivation.priority_queue.policy">Policy Choices</a></span></dt><dt><span class="section"><a href="policy_data_structures.html#motivation.priority_queue.underlying">Underlying Data Structures</a></span></dt><dt><span class="section"><a href="policy_data_structures.html#motivation.priority_queue.binary_heap">Binary Heaps</a></span></dt></dl></dd></dl></dd></dl></dd><dt><span class="section"><a href="policy_data_structures_using.html">Using</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.prereq">Prerequisites</a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.organization">Organization</a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.tutorial">Tutorial</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.tutorial.basic">Basic Use</a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.tutorial.configuring">
Configuring via Template Parameters
</a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.tutorial.traits">
Querying Container Attributes
</a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.tutorial.point_range_iteration">
Point and Range Iteration
</a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.examples">Examples</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.examples.basic">Intermediate Use</a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.examples.query">Querying with <code class="classname">container_traits</code> </a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.examples.container">By Container Method</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.examples.container.hash">Hash-Based</a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.examples.container.branch">Branch-Based</a></span></dt><dt><span class="section"><a href="policy_data_structures_using.html#pbds.using.examples.container.priority_queue">Priority Queues</a></span></dt></dl></dd></dl></dd></dl></dd><dt><span class="section"><a href="policy_data_structures_design.html">Design</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.concepts">Concepts</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.concepts.null_type">Null Policy Classes</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.concepts.associative_semantics">Map and Set Semantics</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#concepts.associative_semantics.set_vs_map">
Distinguishing Between Maps and Sets
</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#concepts.associative_semantics.multi">Alternatives to <code class="classname">std::multiset</code> and <code class="classname">std::multimap</code></a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.concepts.iterator_semantics">Iterator Semantics</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#concepts.iterator_semantics.point_and_range">Point and Range Iterators</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#concepts.iterator_semantics.both">Distinguishing Point and Range Iterators</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.concepts.invalidation">Invalidation Guarantees</a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.concepts.genericity">Genericity</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#concepts.genericity.tag">Tag</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#concepts.genericity.traits">Traits</a></span></dt></dl></dd></dl></dd><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.container">By Container</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.container.hash">hash</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#container.hash.interface">Interface</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#container.hash.details">Details</a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.container.tree">tree</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#container.tree.interface">Interface</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#container.tree.details">Details</a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.container.trie">Trie</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#container.trie.interface">Interface</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#container.trie.details">Details</a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.container.list">List</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#container.list.interface">Interface</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#container.list.details">Details</a></span></dt></dl></dd><dt><span class="section"><a href="policy_data_structures_design.html#pbds.design.container.priority_queue">Priority Queue</a></span></dt><dd><dl><dt><span class="section"><a href="policy_data_structures_design.html#container.priority_queue.interface">Interface</a></span></dt><dt><span class="section"><a href="policy_data_structures_design.html#container.priority_queue.details">Details</a></span></dt></dl></dd></dl></dd></dl></dd><dt><span class="section"><a href="policy_based_data_structures_test.html">Testing</a></span></dt><dd><dl><dt><span class="section"><a href="policy_based_data_structures_test.html#pbds.test.regression">Regression</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#pbds.test.performance">Performance</a></span></dt><dd><dl><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.hash">Hash-Based</a></span></dt><dd><dl><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.hash.text_find">
Text <code class="function">find</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.hash.int_find">
Integer <code class="function">find</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.hash.int_subscript_find">
Integer Subscript <code class="function">find</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.hash.int_subscript_insert">
Integer Subscript <code class="function">insert</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.hash.zlob_int_find">
Integer <code class="function">find</code> with Skewed-Distribution
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.hash.erase_mem">
Erase Memory Use
</a></span></dt></dl></dd><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.branch">Branch-Based</a></span></dt><dd><dl><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.branch.text_insert">
Text <code class="function">insert</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.branch.text_find">
Text <code class="function">find</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.branch.text_lor_find">
Text <code class="function">find</code> with Locality-of-Reference
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.branch.split_join">
<code class="function">split</code> and <code class="function">join</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.branch.order_statistics">
Order-Statistics
</a></span></dt></dl></dd><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.multimap">Multimap</a></span></dt><dd><dl><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.multimap.text_find_small">
Text <code class="function">find</code> with Small Secondary-to-Primary Key Ratios
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.multimap.text_find_large">
Text <code class="function">find</code> with Large Secondary-to-Primary Key Ratios
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.multimap.text_insert_small">
Text <code class="function">insert</code> with Small
Secondary-to-Primary Key Ratios
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.multimap.text_insert_large">
Text <code class="function">insert</code> with Small
Secondary-to-Primary Key Ratios
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.multimap.text_insert_mem_small">
Text <code class="function">insert</code> with Small
Secondary-to-Primary Key Ratios Memory Use
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.multimap.text_insert_mem_large">
Text <code class="function">insert</code> with Small
Secondary-to-Primary Key Ratios Memory Use
</a></span></dt></dl></dd><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue">Priority Queue</a></span></dt><dd><dl><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue.text_push">
Text <code class="function">push</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue.text_push_pop">
Text <code class="function">push</code> and <code class="function">pop</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue.int_push">
Integer <code class="function">push</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue.int_push_pop">
Integer <code class="function">push</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue.text_pop">
Text <code class="function">pop</code> Memory Use
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue.text_join">
Text <code class="function">join</code>
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue.text_modify_up">
Text <code class="function">modify</code> Up
</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#performance.priority_queue.text_modify_down">
Text <code class="function">modify</code> Down
</a></span></dt></dl></dd><dt><span class="section"><a href="policy_based_data_structures_test.html#pbds.test.performance.observations">Observations</a></span></dt><dd><dl><dt><span class="section"><a href="policy_based_data_structures_test.html#observations.associative">Associative</a></span></dt><dt><span class="section"><a href="policy_based_data_structures_test.html#observations.priority_queue">Priority_Queue</a></span></dt></dl></dd></dl></dd></dl></dd><dt><span class="section"><a href="policy_data_structures_ack.html">Acknowledgments</a></span></dt><dt><span class="bibliography"><a href="policy_data_structures.html#pbds.biblio">Bibliography</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="pbds.intro"></a>Intro</h2></div></div></div><p>
This is a library of policy-based elementary data structures:
associative containers and priority queues. It is designed for
high-performance, flexibility, semantic safety, and conformance to
the corresponding containers in <code class="literal">std</code> and
<code class="literal">std::tr1</code> (except for some points where it differs
by design).
</p><p>
</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="pbds.intro.issues"></a>Performance Issues</h3></div></div></div><p>
</p><p>
An attempt is made to categorize the wide variety of possible
container designs in terms of performance-impacting factors. These
performance factors are translated into design policies and
incorporated into container design.
</p><p>
There is tension between unravelling factors into a coherent set of
policies. Every attempt is made to make a minimal set of
factors. However, in many cases multiple factors make for long
template names. Every attempt is made to alias and use typedefs in
the source files, but the generated names for external symbols can
be large for binary files or debuggers.
</p><p>
In many cases, the longer names allow capabilities and behaviours
controlled by macros to also be unamibiguously emitted as distinct
generated names.
</p><p>
Specific issues found while unraveling performance factors in the
design of associative containers and priority queues follow.
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="pbds.intro.issues.associative"></a>Associative</h4></div></div></div><p>
Associative containers depend on their composite policies to a very
large extent. Implicitly hard-wiring policies can hamper their
performance and limit their functionality. An efficient hash-based
container, for example, requires policies for testing key
equivalence, hashing keys, translating hash values into positions
within the hash table, and determining when and how to resize the
table internally. A tree-based container can efficiently support
order statistics, i.e. the ability to query what is the order of
each key within the sequence of keys in the container, but only if
the container is supplied with a policy to internally update
meta-data. There are many other such examples.
</p><p>
Ideally, all associative containers would share the same
interface. Unfortunately, underlying data structures and mapping
semantics differentiate between different containers. For example,
suppose one writes a generic function manipulating an associative
container.
</p><pre class="programlisting">
template<typename Cntnr>
void
some_op_sequence(Cntnr& r_cnt)
{
...
}
</pre><p>
Given this, then what can one assume about the instantiating
container? The answer varies according to its underlying data
structure. If the underlying data structure of
<code class="literal">Cntnr</code> is based on a tree or trie, then the order
of elements is well defined; otherwise, it is not, in general. If
the underlying data structure of <code class="literal">Cntnr</code> is based
on a collision-chaining hash table, then modifying
r_<code class="literal">Cntnr</code> will not invalidate its iterators' order;
if the underlying data structure is a probing hash table, then this
is not the case. If the underlying data structure is based on a tree
or trie, then a reference to the container can efficiently be split;
otherwise, it cannot, in general. If the underlying data structure
is a red-black tree, then splitting a reference to the container is
exception-free; if it is an ordered-vector tree, exceptions can be
thrown.
</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="pbds.intro.issues.priority_queue"></a>Priority Que</h4></div></div></div><p>
Priority queues are useful when one needs to efficiently access a
minimum (or maximum) value as the set of values changes.
</p><p>
Most useful data structures for priority queues have a relatively
simple structure, as they are geared toward relatively simple
requirements. Unfortunately, these structures do not support access
to an arbitrary value, which turns out to be necessary in many
algorithms. Say, decreasing an arbitrary value in a graph
algorithm. Therefore, some extra mechanism is necessary and must be
invented for accessing arbitrary values. There are at least two
alternatives: embedding an associative container in a priority
queue, or allowing cross-referencing through iterators. The first
solution adds significant overhead; the second solution requires a
precise definition of iterator invalidation. Which is the next
point...
</p><p>
Priority queues, like hash-based containers, store values in an
order that is meaningless and undefined externally. For example, a
<code class="code">push</code> operation can internally reorganize the
values. Because of this characteristic, describing a priority
queues' iterator is difficult: on one hand, the values to which
iterators point can remain valid, but on the other, the logical
order of iterators can change unpredictably.
</p><p>
Roughly speaking, any element that is both inserted to a priority
queue (e.g. through <code class="code">push</code>) and removed
from it (e.g., through <code class="code">pop</code>), incurs a
logarithmic overhead (in the amortized sense). Different underlying
data structures place the actual cost differently: some are
optimized for amortized complexity, whereas others guarantee that
specific operations only have a constant cost. One underlying data
structure might be chosen if modifying a value is frequent
(Dijkstra's shortest-path algorithm), whereas a different one might
be chosen otherwise. Unfortunately, an array-based binary heap - an
underlying data structure that optimizes (in the amortized sense)
<code class="code">push</code> and <code class="code">pop</code> operations, differs from the
others in terms of its invalidation guarantees. Other design
decisions also impact the cost and placement of the overhead, at the
expense of more difference in the the kinds of operations that the
underlying data structure can support. These differences pose a
challenge when creating a uniform interface for priority queues.
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="pbds.intro.motivation"></a>Goals</h3></div></div></div><p>
Many fine associative-container libraries were already written,
most notably, the C++ standard's associative containers. Why
then write another library? This section shows some possible
advantages of this library, when considering the challenges in
the introduction. Many of these points stem from the fact that
the ISO C++ process introduced associative-containers in a
two-step process (first standardizing tree-based containers,
only then adding hash-based containers, which are fundamentally
different), did not standardize priority queues as containers,
and (in our opinion) overloads the iterator concept.
</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="pbds.intro.motivation.associative"></a>Associative</h4></div></div></div><p>
</p><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="motivation.associative.policy"></a>Policy Choices</h5></div></div></div><p>
Associative containers require a relatively large number of
policies to function efficiently in various settings. In some
cases this is needed for making their common operations more
efficient, and in other cases this allows them to support a
larger set of operations
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Hash-based containers, for example, support look-up and
insertion methods (<code class="function">find</code> and
<code class="function">insert</code>). In order to locate elements
quickly, they are supplied a hash functor, which instruct
how to transform a key object into some size type; a hash
functor might transform <code class="constant">"hello"</code>
into <code class="constant">1123002298</code>. A hash table, though,
requires transforming each key object into some size-type
type in some specific domain; a hash table with a 128-long
table might transform <code class="constant">"hello"</code> into
position <code class="constant">63</code>. The policy by which the
hash value is transformed into a position within the table
can dramatically affect performance. Hash-based containers
also do not resize naturally (as opposed to tree-based
containers, for example). The appropriate resize policy is
unfortunately intertwined with the policy that transforms
hash value into a position within the table.
</p></li><li class="listitem"><p>
Tree-based containers, for example, also support look-up and
insertion methods, and are primarily useful when maintaining
order between elements is important. In some cases, though,
one can utilize their balancing algorithms for completely
different purposes.
</p><p>
Figure A shows a tree whose each node contains two entries:
a floating-point key, and some size-type
<span class="emphasis"><em>metadata</em></span> (in bold beneath it) that is
the number of nodes in the sub-tree. (The root has key 0.99,
and has 5 nodes (including itself) in its sub-tree.) A
container based on this data structure can obviously answer
efficiently whether 0.3 is in the container object, but it
can also answer what is the order of 0.3 among all those in
the container object: see <a class="xref" href="policy_data_structures.html#biblio.clrs2001" title="Introduction to Algorithms, 2nd edition">[biblio.clrs2001]</a>.
</p><p>
As another example, Figure B shows a tree whose each node
contains two entries: a half-open geometric line interval,
and a number <span class="emphasis"><em>metadata</em></span> (in bold beneath
it) that is the largest endpoint of all intervals in its
sub-tree. (The root describes the interval <code class="constant">[20,
36)</code>, and the largest endpoint in its sub-tree is
99.) A container based on this data structure can obviously
answer efficiently whether <code class="constant">[3, 41)</code> is
in the container object, but it can also answer efficiently
whether the container object has intervals that intersect
<code class="constant">[3, 41)</code>. These types of queries are
very useful in geometric algorithms and lease-management
algorithms.
</p><p>
It is important to note, however, that as the trees are
modified, their internal structure changes. To maintain
these invariants, one must supply some policy that is aware
of these changes. Without this, it would be better to use a
linked list (in itself very efficient for these purposes).
</p></li></ol></div><div class="figure"><a id="idp17613296"></a><p class="title"><strong>Figure 22.1. Node Invariants</strong></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="../images/pbds_node_invariants.png" align="middle" alt="Node Invariants" /></div></div></div><br class="figure-break" /></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="motivation.associative.underlying"></a>Underlying Data Structures</h5></div></div></div><p>
The standard C++ library contains associative containers based on
red-black trees and collision-chaining hash tables. These are
very useful, but they are not ideal for all types of
settings.
</p><p>
The figure below shows the different underlying data structures
currently supported in this library.
</p><div class="figure"><a id="idp17619952"></a><p class="title"><strong>Figure 22.2. Underlying Associative Data Structures</strong></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="../images/pbds_different_underlying_dss_1.png" align="middle" alt="Underlying Associative Data Structures" /></div></div></div><br class="figure-break" /><p>
A shows a collision-chaining hash-table, B shows a probing
hash-table, C shows a red-black tree, D shows a splay tree, E shows
a tree based on an ordered vector(implicit in the order of the
elements), F shows a PATRICIA trie, and G shows a list-based
container with update policies.
</p><p>
Each of these data structures has some performance benefits, in
terms of speed, size or both. For now, note that vector-based trees
and probing hash tables manipulate memory more efficiently than
red-black trees and collision-chaining hash tables, and that
list-based associative containers are very useful for constructing
"multimaps".
</p><p>
Now consider a function manipulating a generic associative
container,
</p><pre class="programlisting">
template<class Cntnr>
int
some_op_sequence(Cntnr &r_cnt)
{
...
}
</pre><p>
Ideally, the underlying data structure
of <code class="classname">Cntnr</code> would not affect what can be
done with <code class="varname">r_cnt</code>. Unfortunately, this is not
the case.
</p><p>
For example, if <code class="classname">Cntnr</code>
is <code class="classname">std::map</code>, then the function can
use
</p><pre class="programlisting">
std::for_each(r_cnt.find(foo), r_cnt.find(bar), foobar)
</pre><p>
in order to apply <code class="classname">foobar</code> to all
elements between <code class="classname">foo</code> and
<code class="classname">bar</code>. If
<code class="classname">Cntnr</code> is a hash-based container,
then this call's results are undefined.
</p><p>
Also, if <code class="classname">Cntnr</code> is tree-based, the type
and object of the comparison functor can be
accessed. If <code class="classname">Cntnr</code> is hash based, these
queries are nonsensical.
</p><p>
There are various other differences based on the container's
underlying data structure. For one, they can be constructed by,
and queried for, different policies. Furthermore:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Containers based on C, D, E and F store elements in a
meaningful order; the others store elements in a meaningless
(and probably time-varying) order. By implication, only
containers based on C, D, E and F can
support <code class="function">erase</code> operations taking an
iterator and returning an iterator to the following element
without performance loss.
</p></li><li class="listitem"><p>
Containers based on C, D, E, and F can be split and joined
efficiently, while the others cannot. Containers based on C
and D, furthermore, can guarantee that this is exception-free;
containers based on E cannot guarantee this.
</p></li><li class="listitem"><p>
Containers based on all but E can guarantee that
erasing an element is exception free; containers based on E
cannot guarantee this. Containers based on all but B and E
can guarantee that modifying an object of their type does
not invalidate iterators or references to their elements,
while containers based on B and E cannot. Containers based
on C, D, and E can furthermore make a stronger guarantee,
namely that modifying an object of their type does not
affect the order of iterators.
</p></li></ol></div><p>
A unified tag and traits system (as used for the C++ standard
library iterators, for example) can ease generic manipulation of
associative containers based on different underlying data
structures.
</p></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="motivation.associative.iterators"></a>Iterators</h5></div></div></div><p>
Iterators are centric to the design of the standard library
containers, because of the container/algorithm/iterator
decomposition that allows an algorithm to operate on a range
through iterators of some sequence. Iterators, then, are useful
because they allow going over a
specific <span class="emphasis"><em>sequence</em></span>. The standard library
also uses iterators for accessing a
specific <span class="emphasis"><em>element</em></span>: when an associative
container returns one through <code class="function">find</code>. The
standard library consistently uses the same types of iterators
for both purposes: going over a range, and accessing a specific
found element. Before the introduction of hash-based containers
to the standard library, this made sense (with the exception of
priority queues, which are discussed later).
</p><p>
Using the standard associative containers together with
non-order-preserving associative containers (and also because of
priority-queues container), there is a possible need for
different types of iterators for self-organizing containers:
the iterator concept seems overloaded to mean two different
things (in some cases). <em><span class="remark"> XXX
"ds_gen.html#find_range">Design::Associative
Containers::Data-Structure Genericity::Point-Type and Range-Type
Methods</span></em>.
</p><div class="section"><div class="titlepage"><div><div><h6 class="title"><a id="associative.iterators.using"></a>Using Point Iterators for Range Operations</h6></div></div></div><p>
Suppose <code class="classname">cntnr</code> is some associative
container, and say <code class="varname">c</code> is an object of
type <code class="classname">cntnr</code>. Then what will be the outcome
of
</p><pre class="programlisting">
std::for_each(c.find(1), c.find(5), foo);
</pre><p>
If <code class="classname">cntnr</code> is a tree-based container
object, then an in-order walk will
apply <code class="classname">foo</code> to the relevant elements,
as in the graphic below, label A. If <code class="varname">c</code> is
a hash-based container, then the order of elements between any
two elements is undefined (and probably time-varying); there is
no guarantee that the elements traversed will coincide with the
<span class="emphasis"><em>logical</em></span> elements between 1 and 5, as in
label B.
</p><div class="figure"><a id="idp17651648"></a><p class="title"><strong>Figure 22.3. Range Iteration in Different Data Structures</strong></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="../images/pbds_point_iterators_range_ops_1.png" align="middle" alt="Node Invariants" /></div></div></div><br class="figure-break" /><p>
In our opinion, this problem is not caused just because
red-black trees are order preserving while
collision-chaining hash tables are (generally) not - it
is more fundamental. Most of the standard's containers
order sequences in a well-defined manner that is
determined by their <span class="emphasis"><em>interface</em></span>:
calling <code class="function">insert</code> on a tree-based
container modifies its sequence in a predictable way, as
does calling <code class="function">push_back</code> on a list or
a vector. Conversely, collision-chaining hash tables,
probing hash tables, priority queues, and list-based
containers (which are very useful for "multimaps") are
self-organizing data structures; the effect of each
operation modifies their sequences in a manner that is
(practically) determined by their
<span class="emphasis"><em>implementation</em></span>.
</p><p>
Consequently, applying an algorithm to a sequence obtained from most
containers may or may not make sense, but applying it to a
sub-sequence of a self-organizing container does not.
</p></div><div class="section"><div class="titlepage"><div><div><h6 class="title"><a id="associative.iterators.cost"></a>Cost to Point Iterators to Enable Range Operations</h6></div></div></div><p>
Suppose <code class="varname">c</code> is some collision-chaining
hash-based container object, and one calls
</p><pre class="programlisting">c.find(3)</pre><p>
Then what composes the returned iterator?
</p><p>
In the graphic below, label A shows the simplest (and
most efficient) implementation of a collision-chaining
hash table. The little box marked
<code class="classname">point_iterator</code> shows an object
that contains a pointer to the element's node. Note that
this "iterator" has no way to move to the next element (
it cannot support
<code class="function">operator++</code>). Conversely, the little
box marked <code class="classname">iterator</code> stores both a
pointer to the element, as well as some other
information (the bucket number of the element). the
second iterator, then, is "heavier" than the first one-
it requires more time and space. If we were to use a
different container to cross-reference into this
hash-table using these iterators - it would take much
more space. As noted above, nothing much can be done by
incrementing these iterators, so why is this extra
information needed?
</p><p>
Alternatively, one might create a collision-chaining hash-table
where the lists might be linked, forming a monolithic total-element
list, as in the graphic below, label B. Here the iterators are as
light as can be, but the hash-table's operations are more
complicated.
</p><div class="figure"><a id="idp17666528"></a><p class="title"><strong>Figure 22.4. Point Iteration in Hash Data Structures</strong></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="../images/pbds_point_iterators_range_ops_2.png" align="middle" alt="Point Iteration in Hash Data Structures" /></div></div></div><br class="figure-break" /><p>
It should be noted that containers based on collision-chaining
hash-tables are not the only ones with this type of behavior;
many other self-organizing data structures display it as well.
</p></div><div class="section"><div class="titlepage"><div><div><h6 class="title"><a id="associative.iterators.invalidation"></a>Invalidation Guarantees</h6></div></div></div><p>Consider the following snippet:</p><pre class="programlisting">
it = c.find(3);
c.erase(5);
</pre><p>
Following the call to <code class="classname">erase</code>, what is the
validity of <code class="classname">it</code>: can it be de-referenced?
can it be incremented?
</p><p>
The answer depends on the underlying data structure of the
container. The graphic below shows three cases: A1 and A2 show
a red-black tree; B1 and B2 show a probing hash-table; C1 and C2
show a collision-chaining hash table.
</p><div class="figure"><a id="idp17675840"></a><p class="title"><strong>Figure 22.5. Effect of erase in different underlying data structures</strong></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="../images/pbds_invalidation_guarantee_erase.png" align="middle" alt="Effect of erase in different underlying data structures" /></div></div></div><br class="figure-break" /><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Erasing 5 from A1 yields A2. Clearly, an iterator to 3 can
be de-referenced and incremented. The sequence of iterators
changed, but in a way that is well-defined by the interface.
</p></li><li class="listitem"><p>
Erasing 5 from B1 yields B2. Clearly, an iterator to 3 is
not valid at all - it cannot be de-referenced or
incremented; the order of iterators changed in a way that is
(practically) determined by the implementation and not by
the interface.
</p></li><li class="listitem"><p>
Erasing 5 from C1 yields C2. Here the situation is more
complicated. On the one hand, there is no problem in
de-referencing <code class="classname">it</code>. On the other hand,
the order of iterators changed in a way that is
(practically) determined by the implementation and not by
the interface.
</p></li></ol></div><p>
So in the standard library containers, it is not always possible
to express whether <code class="varname">it</code> is valid or not. This
is true also for <code class="function">insert</code>. Again, the
iterator concept seems overloaded.
</p></div></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="motivation.associative.functions"></a>Functional</h5></div></div></div><p>
</p><p>
The design of the functional overlay to the underlying data
structures differs slightly from some of the conventions used in
the C++ standard. A strict public interface of methods that
comprise only operations which depend on the class's internal
structure; other operations are best designed as external
functions. (See <a class="xref" href="policy_data_structures.html#biblio.meyers02both" title="Class Template, Member Template - or Both?">[biblio.meyers02both]</a>).With this
rubric, the standard associative containers lack some useful
methods, and provide other methods which would be better
removed.
</p><div class="section"><div class="titlepage"><div><div><h6 class="title"><a id="motivation.associative.functions.erase"></a><code class="function">erase</code></h6></div></div></div><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Order-preserving standard associative containers provide the
method
</p><pre class="programlisting">
iterator
erase(iterator it)
</pre><p>
which takes an iterator, erases the corresponding
element, and returns an iterator to the following
element. Also standardd hash-based associative
containers provide this method. This seemingly
increasesgenericity between associative containers,
since it is possible to use
</p><pre class="programlisting">
typename C::iterator it = c.begin();
typename C::iterator e_it = c.end();
while(it != e_it)
it = pred(*it)? c.erase(it) : ++it;
</pre><p>
in order to erase from a container object <code class="varname">
c</code> all element which match a
predicate <code class="classname">pred</code>. However, in a
different sense this actually decreases genericity: an
integral implication of this method is that tree-based
associative containers' memory use is linear in the total
number of elements they store, while hash-based
containers' memory use is unbounded in the total number of
elements they store. Assume a hash-based container is
allowed to decrease its size when an element is
erased. Then the elements might be rehashed, which means
that there is no "next" element - it is simply
undefined. Consequently, it is possible to infer from the
fact that the standard library's hash-based containers
provide this method that they cannot downsize when
elements are erased. As a consequence, different code is
needed to manipulate different containers, assuming that
memory should be conserved. Therefor, this library's
non-order preserving associative containers omit this
method.
</p></li><li class="listitem"><p>
All associative containers include a conditional-erase method
</p><pre class="programlisting">
template<
class Pred>
size_type
erase_if
(Pred pred)
</pre><p>
which erases all elements matching a predicate. This is probably the
only way to ensure linear-time multiple-item erase which can
actually downsize a container.
</p></li><li class="listitem"><p>
The standard associative containers provide methods for
multiple-item erase of the form
</p><pre class="programlisting">
size_type
erase(It b, It e)
</pre><p>
erasing a range of elements given by a pair of
iterators. For tree-based or trie-based containers, this can
implemented more efficiently as a (small) sequence of split
and join operations. For other, unordered, containers, this
method isn't much better than an external loop. Moreover,
if <code class="varname">c</code> is a hash-based container,
then
</p><pre class="programlisting">
c.erase(c.find(2), c.find(5))
</pre><p>
is almost certain to do something
different than erasing all elements whose keys are between 2
and 5, and is likely to produce other undefined behavior.
</p></li></ol></div></div><div class="section"><div class="titlepage"><div><div><h6 class="title"><a id="motivation.associative.functions.split"></a>
<code class="function">split</code> and <code class="function">join</code>
</h6></div></div></div><p>
It is well-known that tree-based and trie-based container
objects can be efficiently split or joined (See
<a class="xref" href="policy_data_structures.html#biblio.clrs2001" title="Introduction to Algorithms, 2nd edition">[biblio.clrs2001]</a>). Externally splitting or
joining trees is super-linear, and, furthermore, can throw
exceptions. Split and join methods, consequently, seem good
choices for tree-based container methods, especially, since as
noted just before, they are efficient replacements for erasing
sub-sequences.
</p></div><div class="section"><div class="titlepage"><div><div><h6 class="title"><a id="motivation.associative.functions.insert"></a>
<code class="function">insert</code>
</h6></div></div></div><p>
The standard associative containers provide methods of the form
</p><pre class="programlisting">
template<class It>
size_type
insert(It b, It e);
</pre><p>
for inserting a range of elements given by a pair of
iterators. At best, this can be implemented as an external loop,
or, even more efficiently, as a join operation (for the case of
tree-based or trie-based containers). Moreover, these methods seem
similar to constructors taking a range given by a pair of
iterators; the constructors, however, are transactional, whereas
the insert methods are not; this is possibly confusing.
</p></div><div class="section"><div class="titlepage"><div><div><h6 class="title"><a id="motivation.associative.functions.compare"></a>
<code class="function">operator==</code> and <code class="function">operator<=</code>
</h6></div></div></div><p>
Associative containers are parametrized by policies allowing to
test key equivalence: a hash-based container can do this through
its equivalence functor, and a tree-based container can do this
through its comparison functor. In addition, some standard
associative containers have global function operators, like
<code class="function">operator==</code> and <code class="function">operator<=</code>,
that allow comparing entire associative containers.
</p><p>
In our opinion, these functions are better left out. To begin
with, they do not significantly improve over an external
loop. More importantly, however, they are possibly misleading -
<code class="function">operator==</code>, for example, usually checks for
equivalence, or interchangeability, but the associative
container cannot check for values' equivalence, only keys'
equivalence; also, are two containers considered equivalent if
they store the same values in different order? this is an
arbitrary decision.
</p></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="pbds.intro.motivation.priority_queue"></a>Priority Queues</h4></div></div></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="motivation.priority_queue.policy"></a>Policy Choices</h5></div></div></div><p>
Priority queues are containers that allow efficiently inserting
values and accessing the maximal value (in the sense of the
container's comparison functor). Their interface
supports <code class="function">push</code>
and <code class="function">pop</code>. The standard
container <code class="classname">std::priorityqueue</code> indeed support
these methods, but little else. For algorithmic and
software-engineering purposes, other methods are needed:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Many graph algorithms (see
<a class="xref" href="policy_data_structures.html#biblio.clrs2001" title="Introduction to Algorithms, 2nd edition">[biblio.clrs2001]</a>) require increasing a
value in a priority queue (again, in the sense of the
container's comparison functor), or joining two
priority-queue objects.
</p></li><li class="listitem"><p>The return type of <code class="classname">priority_queue</code>'s
<code class="function">push</code> method is a point-type iterator, which can
be used for modifying or erasing arbitrary values. For
example:</p><pre class="programlisting">
priority_queue<int> p;
priority_queue<int>::point_iterator it = p.push(3);
p.modify(it, 4);
</pre><p>These types of cross-referencing operations are necessary
for making priority queues useful for different applications,
especially graph applications.</p></li><li class="listitem"><p>
It is sometimes necessary to erase an arbitrary value in a
priority queue. For example, consider
the <code class="function">select</code> function for monitoring
file descriptors:
</p><pre class="programlisting">
int
select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds,
struct timeval *timeout);
</pre><p>
then, as the select documentation states:
</p><p>
<span class="quote">“<span class="quote">
The nfds argument specifies the range of file
descriptors to be tested. The select() function tests file
descriptors in the range of 0 to nfds-1.</span>”</span>
</p><p>
It stands to reason, therefore, that we might wish to
maintain a minimal value for <code class="varname">nfds</code>, and
priority queues immediately come to mind. Note, though, that
when a socket is closed, the minimal file description might
change; in the absence of an efficient means to erase an
arbitrary value from a priority queue, we might as well
avoid its use altogether.
</p><p>
The standard containers typically support iterators. It is
somewhat unusual
for <code class="classname">std::priority_queue</code> to omit them
(See <a class="xref" href="policy_data_structures.html#biblio.meyers01stl" title="Effective STL: 50 Specific Ways to Improve Your Use of the Standard Template Library">[biblio.meyers01stl]</a>). One might
ask why do priority queues need to support iterators, since
they are self-organizing containers with a different purpose
than abstracting sequences. There are several reasons:
</p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p>
Iterators (even in self-organizing containers) are
useful for many purposes: cross-referencing
containers, serialization, and debugging code that uses
these containers.
</p></li><li class="listitem"><p>
The standard library's hash-based containers support
iterators, even though they too are self-organizing
containers with a different purpose than abstracting
sequences.
</p></li><li class="listitem"><p>
In standard-library-like containers, it is natural to specify the
interface of operations for modifying a value or erasing
a value (discussed previously) in terms of a iterators.
It should be noted that the standard
containers also use iterators for accessing and
manipulating a specific value. In hash-based
containers, one checks the existence of a key by
comparing the iterator returned by <code class="function">find</code> to the
iterator returned by <code class="function">end</code>, and not by comparing a
pointer returned by <code class="function">find</code> to <span class="type">NULL</span>.
</p></li></ol></div></li></ol></div></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="motivation.priority_queue.underlying"></a>Underlying Data Structures</h5></div></div></div><p>
There are three main implementations of priority queues: the
first employs a binary heap, typically one which uses a
sequence; the second uses a tree (or forest of trees), which is
typically less structured than an associative container's tree;
the third simply uses an associative container. These are
shown in the figure below with labels A1 and A2, B, and C.
</p><div class="figure"><a id="idp17743424"></a><p class="title"><strong>Figure 22.6. Underlying Priority Queue Data Structures</strong></p><div class="figure-contents"><div class="mediaobject" align="center"><img src="../images/pbds_different_underlying_dss_2.png" align="middle" alt="Underlying Priority Queue Data Structures" /></div></div></div><br class="figure-break" /><p>
No single implementation can completely replace any of the
others. Some have better <code class="function">push</code>
and <code class="function">pop</code> amortized performance, some have
better bounded (worst case) response time than others, some
optimize a single method at the expense of others, etc. In
general the "best" implementation is dictated by the specific
problem.
</p><p>
As with associative containers, the more implementations
co-exist, the more necessary a traits mechanism is for handling
generic containers safely and efficiently. This is especially
important for priority queues, since the invalidation guarantees
of one of the most useful data structures - binary heaps - is
markedly different than those of most of the others.
</p></div><div class="section"><div class="titlepage"><div><div><h5 class="title"><a id="motivation.priority_queue.binary_heap"></a>Binary Heaps</h5></div></div></div><p>
Binary heaps are one of the most useful underlying
data structures for priority queues. They are very efficient in
terms of memory (since they don't require per-value structure
metadata), and have the best amortized <code class="function">push</code> and
<code class="function">pop</code> performance for primitive types like
<span class="type">int</span>.
</p><p>
The standard library's <code class="classname">priority_queue</code>
implements this data structure as an adapter over a sequence,
typically
<code class="classname">std::vector</code>
or <code class="classname">std::deque</code>, which correspond to labels
A1 and A2 respectively in the graphic above.
</p><p>
This is indeed an elegant example of the adapter concept and
the algorithm/container/iterator decomposition. (See <a class="xref" href="policy_data_structures.html#biblio.nelson96stlpq" title="Priority Queues and the STL">[biblio.nelson96stlpq]</a>). There are
several reasons why a binary-heap priority queue
may be better implemented as a container instead of a
sequence adapter:
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
<code class="classname">std::priority_queue</code> cannot erase values
from its adapted sequence (irrespective of the sequence
type). This means that the memory use of
an <code class="classname">std::priority_queue</code> object is always
proportional to the maximal number of values it ever contained,
and not to the number of values that it currently
contains. (See <code class="filename">performance/priority_queue_text_pop_mem_usage.cc</code>.)
This implementation of binary heaps acts very differently than
other underlying data structures (See also pairing heaps).
</p></li><li class="listitem"><p>
Some combinations of adapted sequences and value types
are very inefficient or just don't make sense. If one uses
<code class="classname">std::priority_queue<std::vector<std::string>
> ></code>, for example, then not only will each
operation perform a logarithmic number of
<code class="classname">std::string</code> assignments, but, furthermore, any
operation (including <code class="function">pop</code>) can render the container
useless due to exceptions. Conversely, if one uses
<code class="classname">std::priority_queue<std::deque<int> >
></code>, then each operation uses incurs a logarithmic
number of indirect accesses (through pointers) unnecessarily.
It might be better to let the container make a conservative
deduction whether to use the structure in the graphic above, labels A1 or A2.
</p></li><li class="listitem"><p>
There does not seem to be a systematic way to determine
what exactly can be done with the priority queue.
</p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p>
If <code class="classname">p</code> is a priority queue adapting an
<code class="classname">std::vector</code>, then it is possible to iterate over
all values by using <code class="function">&p.top()</code> and
<code class="function">&p.top() + p.size()</code>, but this will not work
if <code class="varname">p</code> is adapting an <code class="classname">std::deque</code>; in any
case, one cannot use <code class="classname">p.begin()</code> and
<code class="classname">p.end()</code>. If a different sequence is adapted, it
is even more difficult to determine what can be
done.
</p></li><li class="listitem"><p>
If <code class="varname">p</code> is a priority queue adapting an
<code class="classname">std::deque</code>, then the reference return by
</p><pre class="programlisting">
p.top()
</pre><p>
will remain valid until it is popped,
but if <code class="varname">p</code> adapts an <code class="classname">std::vector</code>, the
next <code class="function">push</code> will invalidate it. If a different
sequence is adapted, it is even more difficult to
determine what can be done.
</p></li></ol></div></li><li class="listitem"><p>
Sequence-based binary heaps can still implement
linear-time <code class="function">erase</code> and <code class="function">modify</code> operations.
This means that if one needs to erase a small
(say logarithmic) number of values, then one might still
choose this underlying data structure. Using
<code class="classname">std::priority_queue</code>, however, this will generally
change the order of growth of the entire sequence of
operations.
</p></li></ol></div></div></div></div></div><div class="bibliography"><div class="titlepage"><div><div><h2 class="title"><a id="pbds.biblio"></a>Bibliography</h2></div></div></div><div class="biblioentry"><a id="biblio.abrahams97exception"></a><p>[biblio.abrahams97exception] <span class="title"><em>
<a class="link" href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/1997/N1075.pdf" target="_top">
STL Exception Handling Contract
</a>
</em>. </span><span class="date">1997. </span><span class="author"><span class="firstname">
Dave
</span> <span class="surname">
Abrahams
</span>. </span><span class="publisher"><span class="publishername">
ISO SC22/WG21
. </span></span></p></div><div class="biblioentry"><a id="biblio.alexandrescu01modern"></a><p>[biblio.alexandrescu01modern] <span class="title"><em>
Modern C++ Design: Generic Programming and Design Patterns Applied
</em>. </span><span class="date">
2001
. </span><span class="author"><span class="firstname">
Andrei
</span> <span class="surname">
Alexandrescu
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.andrew04mtf"></a><p>[biblio.andrew04mtf] <span class="title"><em>
MTF, Bit, and COMB: A Guide to Deterministic and Randomized
Algorithms for the List Update Problem
</em>. </span><span class="authorgroup"><span class="firstname">
K.
</span> <span class="surname">
Andrew
</span> and <span class="firstname">
D.
</span> <span class="surname">
Gleich
</span>. </span></p></div><div class="biblioentry"><a id="biblio.austern00noset"></a><p>[biblio.austern00noset] <span class="title"><em>
Why You Shouldn't Use set - and What You Should Use Instead
</em>. </span><span class="date">
April, 2000
. </span><span class="author"><span class="firstname">
Matthew
</span> <span class="surname">
Austern
</span>. </span><span class="publisher"><span class="publishername">
C++ Report
. </span></span></p></div><div class="biblioentry"><a id="biblio.austern01htprop"></a><p>[biblio.austern01htprop] <span class="title"><em>
<a class="link" href="http://www.open-std.org/JTC1/sc22/wg21/docs/papers/2001/n1326.html" target="_top">
A Proposal to Add Hashtables to the Standard Library
</a>
</em>. </span><span class="date">
2001
. </span><span class="author"><span class="firstname">
Matthew
</span> <span class="surname">
Austern
</span>. </span><span class="publisher"><span class="publishername">
ISO SC22/WG21
. </span></span></p></div><div class="biblioentry"><a id="biblio.austern98segmentedit"></a><p>[biblio.austern98segmentedit] <span class="title"><em>
Segmented iterators and hierarchical algorithms
</em>. </span><span class="date">
April, 1998
. </span><span class="author"><span class="firstname">
Matthew
</span> <span class="surname">
Austern
</span>. </span><span class="publisher"><span class="publishername">
Generic Programming
. </span></span></p></div><div class="biblioentry"><a id="biblio.dawestimer"></a><p>[biblio.dawestimer] <span class="title"><em>
<a class="link" href="www.boost.org/doc/libs/release/libs/timer/" target="_top">
Boost Timer Library
</a>
</em>. </span><span class="author"><span class="firstname">
Beeman
</span> <span class="surname">
Dawes
</span>. </span><span class="publisher"><span class="publishername">
Boost
. </span></span></p></div><div class="biblioentry"><a id="biblio.clearypool"></a><p>[biblio.clearypool] <span class="title"><em>
<a class="link" href="www.boost.org/doc/libs/release/libs/pool/" target="_top">
Boost Pool Library
</a>
</em>. </span><span class="author"><span class="firstname">
Stephen
</span> <span class="surname">
Cleary
</span>. </span><span class="publisher"><span class="publishername">
Boost
. </span></span></p></div><div class="biblioentry"><a id="biblio.maddocktraits"></a><p>[biblio.maddocktraits] <span class="title"><em>
<a class="link" href="www.boost.org/doc/libs/release/libs/type_traits/" target="_top">
Boost Type Traits Library
</a>
</em>. </span><span class="authorgroup"><span class="firstname">
Maddock
</span> <span class="surname">
John
</span> and <span class="firstname">
Stephen
</span> <span class="surname">
Cleary
</span>. </span><span class="publisher"><span class="publishername">
Boost
. </span></span></p></div><div class="biblioentry"><a id="biblio.brodal96priority"></a><p>[biblio.brodal96priority] <span class="title"><em>
<a class="link" href="https://dl.acm.org/citation.cfm?id=313883" target="_top">
Worst-case efficient priority queues
</a>
</em>. </span><span class="author"><span class="firstname">
Gerth
</span> <span class="surname">
Stolting Brodal
</span>. </span></p></div><div class="biblioentry"><a id="biblio.bulkamayheweff"></a><p>[biblio.bulkamayheweff] <span class="title"><em>
Efficient C++ Programming Techniques
</em>. </span><span class="date">
1997
. </span><span class="authorgroup"><span class="firstname">
D.
</span> <span class="surname">
Bulka
</span> and <span class="firstname">
D.
</span> <span class="surname">
Mayhew
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.clrs2001"></a><p>[biblio.clrs2001] <span class="title"><em>
Introduction to Algorithms, 2nd edition
</em>. </span><span class="date">
2001
. </span><span class="authorgroup"><span class="firstname">
T. H.
</span> <span class="surname">
Cormen
</span>, <span class="firstname">
C. E.
</span> <span class="surname">
Leiserson
</span>, <span class="firstname">
R. L.
</span> <span class="surname">
Rivest
</span>, and <span class="firstname">
C.
</span> <span class="surname">
Stein
</span>. </span><span class="publisher"><span class="publishername">
MIT Press
. </span></span></p></div><div class="biblioentry"><a id="biblio.dubhashi98neg"></a><p>[biblio.dubhashi98neg] <span class="title"><em>
Balls and bins: A study in negative dependence
</em>. </span><span class="date">
1998
. </span><span class="authorgroup"><span class="firstname">
D.
</span> <span class="surname">
Dubashi
</span> and <span class="firstname">
D.
</span> <span class="surname">
Ranjan
</span>. </span><span class="publisher"><span class="publishername">
Random Structures and Algorithms 13
. </span></span></p></div><div class="biblioentry"><a id="biblio.fagin79extendible"></a><p>[biblio.fagin79extendible] <span class="title"><em>
Extendible hashing - a fast access method for dynamic files
</em>. </span><span class="date">
1979
. </span><span class="authorgroup"><span class="firstname">
R.
</span> <span class="surname">
Fagin
</span>, <span class="firstname">
J.
</span> <span class="surname">
Nievergelt
</span>, <span class="firstname">
N.
</span> <span class="surname">
Pippenger
</span>, and <span class="firstname">
H. R.
</span> <span class="surname">
Strong
</span>. </span><span class="publisher"><span class="publishername">
ACM Trans. Database Syst. 4
. </span></span></p></div><div class="biblioentry"><a id="biblio.filliatre2000ptset"></a><p>[biblio.filliatre2000ptset] <span class="title"><em>
<a class="link" href="http://cristal.inria.fr/~frisch/icfp06_contest/advtr/applyOmatic/ptset.ml" target="_top">
Ptset: Sets of integers implemented as Patricia trees
</a>
</em>. </span><span class="date">
2000
. </span><span class="author"><span class="firstname">
Jean-Christophe
</span> <span class="surname">
Filliatre
</span>. </span></p></div><div class="biblioentry"><a id="biblio.fredman86pairing"></a><p>[biblio.fredman86pairing] <span class="title"><em>
<a class="link" href="http://www.cs.cmu.edu/~sleator/papers/pairing-heaps.pdf" target="_top">
The pairing heap: a new form of self-adjusting heap
</a>
</em>. </span><span class="date">
1986
. </span><span class="authorgroup"><span class="firstname">
M. L.
</span> <span class="surname">
Fredman
</span>, <span class="firstname">
R.
</span> <span class="surname">
Sedgewick
</span>, <span class="firstname">
D. D.
</span> <span class="surname">
Sleator
</span>, and <span class="firstname">
R. E.
</span> <span class="surname">
Tarjan
</span>. </span></p></div><div class="biblioentry"><a id="biblio.gof"></a><p>[biblio.gof] <span class="title"><em>
Design Patterns - Elements of Reusable Object-Oriented Software
</em>. </span><span class="date">
1995
. </span><span class="authorgroup"><span class="firstname">
E.
</span> <span class="surname">
Gamma
</span>, <span class="firstname">
R.
</span> <span class="surname">
Helm
</span>, <span class="firstname">
R.
</span> <span class="surname">
Johnson
</span>, and <span class="firstname">
J.
</span> <span class="surname">
Vlissides
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.garg86order"></a><p>[biblio.garg86order] <span class="title"><em>
Order-preserving key transformations
</em>. </span><span class="date">
1986
. </span><span class="authorgroup"><span class="firstname">
A. K.
</span> <span class="surname">
Garg
</span> and <span class="firstname">
C. C.
</span> <span class="surname">
Gotlieb
</span>. </span><span class="publisher"><span class="publishername">
Trans. Database Syst. 11
. </span></span></p></div><div class="biblioentry"><a id="biblio.hyslop02making"></a><p>[biblio.hyslop02making] <span class="title"><em>
Making a real hash of things
</em>. </span><span class="date">
May 2002
. </span><span class="authorgroup"><span class="firstname">
J.
</span> <span class="surname">
Hyslop
</span> and <span class="firstname">
Herb
</span> <span class="surname">
Sutter
</span>. </span><span class="publisher"><span class="publishername">
C++ Report
. </span></span></p></div><div class="biblioentry"><a id="biblio.jossutis01stl"></a><p>[biblio.jossutis01stl] <span class="title"><em>
The C++ Standard Library - A Tutorial and Reference
</em>. </span><span class="date">
2001
. </span><span class="author"><span class="firstname">
N. M.
</span> <span class="surname">
Jossutis
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.kt99fat_heaps"></a><p>[biblio.kt99fat_heaps] <span class="title"><em>
<a class="link" href="http://www.cs.princeton.edu/research/techreps/TR-597-99" target="_top">
New Heap Data Structures
</a>
</em>. </span><span class="date">
1999
. </span><span class="authorgroup"><span class="firstname">
Haim
</span> <span class="surname">
Kaplan
</span> and <span class="firstname">
Robert E.
</span> <span class="surname">
Tarjan
</span>. </span></p></div><div class="biblioentry"><a id="biblio.kleft00sets"></a><p>[biblio.kleft00sets] <span class="title"><em>
Are Set Iterators Mutable or Immutable?
</em>. </span><span class="date">
October 2000
. </span><span class="authorgroup"><span class="firstname">
Angelika
</span> <span class="surname">
Langer
</span> and <span class="firstname">
Klaus
</span> <span class="surname">
Kleft
</span>. </span><span class="publisher"><span class="publishername">
C/C++ Users Jornal
. </span></span></p></div><div class="biblioentry"><a id="biblio.knuth98sorting"></a><p>[biblio.knuth98sorting] <span class="title"><em>
The Art of Computer Programming - Sorting and Searching
</em>. </span><span class="date">
1998
. </span><span class="author"><span class="firstname">
D. E.
</span> <span class="surname">
Knuth
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.liskov98data"></a><p>[biblio.liskov98data] <span class="title"><em>
Data abstraction and hierarchy
</em>. </span><span class="date">
May 1998
. </span><span class="author"><span class="firstname">
B.
</span> <span class="surname">
Liskov
</span>. </span><span class="publisher"><span class="publishername">
SIGPLAN Notices 23
. </span></span></p></div><div class="biblioentry"><a id="biblio.litwin80lh"></a><p>[biblio.litwin80lh] <span class="title"><em>
Linear hashing: A new tool for file and table addressing
</em>. </span><span class="date">
June 1980
. </span><span class="author"><span class="firstname">
W.
</span> <span class="surname">
Litwin
</span>. </span><span class="publisher"><span class="publishername">
Proceedings of International Conference on Very Large Data Bases
. </span></span></p></div><div class="biblioentry"><a id="biblio.maverik_lowerbounds"></a><p>[biblio.maverik_lowerbounds] <span class="title"><em>
<a class="link" href="http://magic.aladdin.cs.cmu.edu/2005/08/01/deamortization-part-2-binomial-heaps" target="_top">
Deamortization - Part 2: Binomial Heaps
</a>
</em>. </span><span class="date">
2005
. </span><span class="author"><span class="firstname">
Maverik
</span> <span class="surname">
Woo
</span>. </span></p></div><div class="biblioentry"><a id="biblio.meyers96more"></a><p>[biblio.meyers96more] <span class="title"><em>
More Effective C++: 35 New Ways to Improve Your Programs and Designs
</em>. </span><span class="date">
1996
. </span><span class="author"><span class="firstname">
Scott
</span> <span class="surname">
Meyers
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.meyers00nonmember"></a><p>[biblio.meyers00nonmember] <span class="title"><em>
How Non-Member Functions Improve Encapsulation
</em>. </span><span class="date">
2000
. </span><span class="author"><span class="firstname">
Scott
</span> <span class="surname">
Meyers
</span>. </span><span class="publisher"><span class="publishername">
C/C++ Users Journal
. </span></span></p></div><div class="biblioentry"><a id="biblio.meyers01stl"></a><p>[biblio.meyers01stl] <span class="title"><em>
Effective STL: 50 Specific Ways to Improve Your Use of the Standard Template Library
</em>. </span><span class="date">
2001
. </span><span class="author"><span class="firstname">
Scott
</span> <span class="surname">
Meyers
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.meyers02both"></a><p>[biblio.meyers02both] <span class="title"><em>
Class Template, Member Template - or Both?
</em>. </span><span class="date">
2003
. </span><span class="author"><span class="firstname">
Scott
</span> <span class="surname">
Meyers
</span>. </span><span class="publisher"><span class="publishername">
C/C++ Users Journal
. </span></span></p></div><div class="biblioentry"><a id="biblio.motwani95random"></a><p>[biblio.motwani95random] <span class="title"><em>
Randomized Algorithms
</em>. </span><span class="date">
2003
. </span><span class="authorgroup"><span class="firstname">
R.
</span> <span class="surname">
Motwani
</span> and <span class="firstname">
P.
</span> <span class="surname">
Raghavan
</span>. </span><span class="publisher"><span class="publishername">
Cambridge University Press
. </span></span></p></div><div class="biblioentry"><a id="biblio.mscom"></a><p>[biblio.mscom] <span class="title"><em>
<a class="link" href="https://www.microsoft.com/com/" target="_top">
COM: Component Model Object Technologies
</a>
</em>. </span><span class="publisher"><span class="publishername">
Microsoft
. </span></span></p></div><div class="biblioentry"><a id="biblio.musser95rationale"></a><p>[biblio.musser95rationale] <span class="title"><em>
Rationale for Adding Hash Tables to the C++ Standard Template Library
</em>. </span><span class="date">
1995
. </span><span class="author"><span class="firstname">
David R.
</span> <span class="surname">
Musser
</span>. </span></p></div><div class="biblioentry"><a id="biblio.musser96stltutorial"></a><p>[biblio.musser96stltutorial] <span class="title"><em>
STL Tutorial and Reference Guide
</em>. </span><span class="date">
1996
. </span><span class="authorgroup"><span class="firstname">
David R.
</span> <span class="surname">
Musser
</span> and <span class="firstname">
A.
</span> <span class="surname">
Saini
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.nelson96stlpq"></a><p>[biblio.nelson96stlpq] <span class="title"><em>
<a class="link" href="http://www.dogma.net/markn/articles/pq_stl/priority.htm" target="_top">Priority Queues and the STL
</a>
</em>. </span><span class="date">
January 1996
. </span><span class="author"><span class="firstname">
Mark
</span> <span class="surname">
Nelson
</span>. </span><span class="publisher"><span class="publishername">
Dr. Dobbs Journal
. </span></span></p></div><div class="biblioentry"><a id="biblio.okasaki98mereable"></a><p>[biblio.okasaki98mereable] <span class="title"><em>
Fast mergeable integer maps
</em>. </span><span class="date">
September 1998
. </span><span class="authorgroup"><span class="firstname">
C.
</span> <span class="surname">
Okasaki
</span> and <span class="firstname">
A.
</span> <span class="surname">
Gill
</span>. </span><span class="publisher"><span class="publishername">
In Workshop on ML
. </span></span></p></div><div class="biblioentry"><a id="biblio.sgi_stl"></a><p>[biblio.sgi_stl] <span class="title"><em>
<a class="link" href="http://www.sgi.com/tech/stl/" target="_top">
Standard Template Library Programmer's Guide
</a>
</em>. </span><span class="author"><span class="firstname">
Matt
</span> <span class="surname">
Austern
</span>. </span><span class="publisher"><span class="publishername">
SGI
. </span></span></p></div><div class="biblioentry"><a id="biblio.select_man"></a><p>[biblio.select_man] <span class="title"><em>
<a class="link" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/select.html" target="_top">
select
</a>
</em>. </span></p></div><div class="biblioentry"><a id="biblio.sleator84amortized"></a><p>[biblio.sleator84amortized] <span class="title"><em>
Amortized Efficiency of List Update Problems
</em>. </span><span class="date">
1984
. </span><span class="authorgroup"><span class="firstname">
D. D.
</span> <span class="surname">
Sleator
</span> and <span class="firstname">
R. E.
</span> <span class="surname">
Tarjan
</span>. </span><span class="publisher"><span class="publishername">
ACM Symposium on Theory of Computing
. </span></span></p></div><div class="biblioentry"><a id="biblio.sleator85self"></a><p>[biblio.sleator85self] <span class="title"><em>
Self-Adjusting Binary Search Trees
</em>. </span><span class="date">
1985
. </span><span class="authorgroup"><span class="firstname">
D. D.
</span> <span class="surname">
Sleator
</span> and <span class="firstname">
R. E.
</span> <span class="surname">
Tarjan
</span>. </span><span class="publisher"><span class="publishername">
ACM Symposium on Theory of Computing
. </span></span></p></div><div class="biblioentry"><a id="biblio.stepanov94standard"></a><p>[biblio.stepanov94standard] <span class="title"><em>
The Standard Template Library
</em>. </span><span class="date">
1984
. </span><span class="authorgroup"><span class="firstname">
A. A.
</span> <span class="surname">
Stepanov
</span> and <span class="firstname">
M.
</span> <span class="surname">
Lee
</span>. </span></p></div><div class="biblioentry"><a id="biblio.stroustrup97cpp"></a><p>[biblio.stroustrup97cpp] <span class="title"><em>
The C++ Programming Langugage
</em>. </span><span class="date">
1997
. </span><span class="author"><span class="firstname">
Bjarne
</span> <span class="surname">
Stroustrup
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.vandevoorde2002cpptemplates"></a><p>[biblio.vandevoorde2002cpptemplates] <span class="title"><em>
C++ Templates: The Complete Guide
</em>. </span><span class="date">
2002
. </span><span class="authorgroup"><span class="firstname">
D.
</span> <span class="surname">
Vandevoorde
</span> and <span class="firstname">
N. M.
</span> <span class="surname">
Josuttis
</span>. </span><span class="publisher"><span class="publishername">
Addison-Wesley Publishing Company
. </span></span></p></div><div class="biblioentry"><a id="biblio.wickland96thirty"></a><p>[biblio.wickland96thirty] <span class="title"><em>
<a class="link" href="http://myweb.wvnet.edu/~gsa00121/books/amongdead30.zip" target="_top">
Thirty Years Among the Dead
</a>
</em>. </span><span class="date">
1996
. </span><span class="author"><span class="firstname">
C. A.
</span> <span class="surname">
Wickland
</span>. </span><span class="publisher"><span class="publishername">
National Psychological Institute
. </span></span></p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bitmap_allocator_impl.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="policy_data_structures_using.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Implementation </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Using</td></tr></table></div></body></html>
|