-
Notifications
You must be signed in to change notification settings - Fork 1
Expand file tree
/
Copy pathreduce.html
More file actions
429 lines (361 loc) · 37.1 KB
/
Copy pathreduce.html
File metadata and controls
429 lines (361 loc) · 37.1 KB
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
<!doctype html>
<html class="cpprefjp" lang="ja" itemscope="" itemtype="http://schema.org/WebPage">
<head>
<!-- Google tag (gtag.js) -->
<script async src="https://www.googletagmanager.com/gtag/js?id=G-NXNBNVBTJS"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'G-NXNBNVBTJS');
</script>
<meta charset="UTF-8">
<title>std::reduce - cpprefjp C++日本語リファレンス</title>
<meta name="viewport" content="width=device-width,initial-scale=1">
<meta name="keywords" content="
C++,標準ライブラリ,リファレンス,ドキュメント,STL,std,numeric,std,function template,cpp17
">
<meta name="title" content="std::reduce - cpprefjp C++日本語リファレンス" />
<meta itemprop="name" content="std::reduce - cpprefjp C++日本語リファレンス" />
<meta property="og:title" content="std::reduce - cpprefjp C++日本語リファレンス" />
<meta property="og:url" content="https://cpprefjp.github.io/reference/numeric/reduce.html" />
<meta property="og:site_name" content="cpprefjp - C++日本語リファレンス" />
<meta property="og:type" content="article" />
<meta property="og:description" content="`reduce()`は、イテレータ範囲`[first, last)`を集計する関数である。[`accumulate()`](accumulate.md)関数は範囲の先頭から順に要素を集計するが、この関数は並列計算のために集計順を規定しない。" />
<meta name="twitter:card" content="summary" />
<meta name="twitter:title" content="std::reduce - cpprefjp C++日本語リファレンス" />
<meta name="twitter:url" content="https://cpprefjp.github.io/reference/numeric/reduce.html" />
<meta name="twitter:description" content="`reduce()`は、イテレータ範囲`[first, last)`を集計する関数である。[`accumulate()`](accumulate.md)関数は範囲の先頭から順に要素を集計するが、この関数は並列計算のために集計順を規定しない。" />
<link rel="alternate" type="application/atom+xml" title="Atom" href="https://cpprefjp.github.io/rss.xml" />
<link rel="apple-touch-icon" sizes="180x180" href="../../static/favicons/apple-touch-icon.png?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc">
<link rel="icon" type="image/png" sizes="32x32" href="../../static/favicons/favicon-32x32.png?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc">
<link rel="icon" type="image/png" sizes="16x16" href="../../static/favicons/favicon-16x16.png?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc">
<link rel="manifest" href="../../manifest.json?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc">
<meta name="theme-color" content="#f5f8fc">
<link rel="stylesheet" href="../../static/pygments/default.css?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc">
<!-- <link rel="stylesheet" href="../../static/css/root.css"> -->
<link href="../../static/kunai/css/kunai-stage-0.css?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc" rel="stylesheet">
<link href="../../static/kunai/css/kunai-stage-1.css?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc" rel="stylesheet">
<link href="../../static/kunai/css/kunai-stage-2.css?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc" rel="stylesheet">
<link href="../../static/kunai/css/kunai-stage-3.css?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc" rel="stylesheet">
<script type="text/javascript" src="../../static/kunai/js/kunai-vendor.js?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc"></script>
<script type="text/javascript" src="../../static/kunai/js/kunai.js?cachebust=557cd0469f26f0f797224f46d1b6e764266f07cc"></script>
<script type="text/javascript">
document.addEventListener('DOMContentLoaded', function() {
var kn = new Kunai;
kn.cpprefjp();
});
</script>
</head>
<body>
<header data-kunai-mdinfo="{"meta": {"header": ["numeric"], "namespace": ["std"], "id-type": ["function template"], "cpp": ["cpp17"]}, "sources": [{"id": "98aea963e1a0f224973f2193197038d13d5011d5", "source": "#include <iostream>\n#include <vector>\n#include <numeric>\n\nint main()\n{\n const std::vector<int> v = {1, 2, 3, 4, 5};\n\n // (1) : \u5408\u8a08\u5024\u3092\u6c42\u3081\u308b\n // \u30a4\u30c6\u30ec\u30fc\u30bf\u306e\u8981\u7d20\u578b\u3067\u96c6\u8a08\u3055\u308c\u308b\n int sum = std::reduce(v.begin(), v.end());\n std::cout << \"sum : \" << sum << std::endl;\n\n // (2) : \u5408\u8a08\u5024\u3092long long\u578b\u3068\u3057\u3066\u6c42\u3081\u308b\n // reduce\u306e\u7b2c3\u5f15\u6570\u304clong long\u578b\u306e\u30bc\u30ed\u3092\u8868\u30590LL\u306b\u306a\u3063\u3066\u3044\u308b\u3053\u3068\u306b\u6ce8\u610f\n // reduce\u306e\u623b\u308a\u5024\u578b\u306f\u3001\u7b2c3\u5f15\u6570\u306e\u578b\u3068\u306a\u308b\u305f\u3081\u3001\u5909\u6570sum_ll\u306e\u578b\u306flong long\n auto sum_ll = std::reduce(v.begin(), v.end(), 0LL);\n std::cout << \"sum_ll : \" << sum_ll << std::endl;\n\n // (3) : \u4efb\u610f\u306e\u4e8c\u9805\u6f14\u7b97\u3092\u884c\u3046\n // \u3053\u3053\u3067\u306f\u3001\u521d\u671f\u5024\u30921\u3068\u3057\u3066\u3001\u5168\u3066\u306e\u8981\u7d20\u3092\u639b\u3051\u5408\u308f\u305b\u3066\u3044\u308b\n int product = std::reduce(v.begin(), v.end(), 1, [](int acc, int i) {\n return acc * i;\n });\n std::cout << \"product : \" << product << std::endl;\n}\n"}], "page_id": ["reference", "numeric", "reduce"]}">
<nav class="navbar navbar-default" role="navigation">
<div class="container-fluid">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar-collapse">
<span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="../../index.html">
<div class="title-wrapper clearfix">
<div class="title">cpprefjp - C++日本語リファレンス</div>
</div>
</a>
</div>
<div class="collapse navbar-collapse" id="navbar-collapse">
<ul class="nav navbar-nav navbar-right">
<li>
<div class="google-search">
<script>
(function() {
var cx = '013316413321391058734:ji_u66hl7hq';
var gcse = document.createElement('script');
gcse.type = 'text/javascript';
gcse.async = true;
gcse.src = (document.location.protocol == 'https:' ? 'https:' : 'http:') +
'//www.google.com/cse/cse.js?cx=' + cx;
var s = document.getElementsByTagName('script')[0];
s.parentNode.insertBefore(gcse, s);
})();
</script>
<div class="gcse-search"></div>
</div>
</li>
<li>
<a href="https://github.com/cpprefjp/site">GitHub Project</a>
</li>
</ul>
</div>
</div>
</nav>
</header>
<main id="main" role="main">
<div class="container-fluid">
<div class="row">
<div class="col-sm-9 col-sm-push-3" itemscope itemtype="http://schema.org/Article">
<div class="row">
<div class="col-sm-12 google-search-result">
<gcse:searchresults></gcse:searchresults>
</div>
</div>
<div class="row">
<div class="col-sm-12 content-header">
<ol class="breadcrumb">
<li itemscope itemtype="http://www.schema.org/SiteNavigationElement">
<span>
<a href="../../index.html" itemprop="url">
<i class="fa fa-fw fa-home"></i>
</a>
</span>
</li>
<li itemscope itemtype="http://www.schema.org/SiteNavigationElement">
<span>
<a href="../../reference.html" itemprop="url">
<span itemprop="name">リファレンス</span>
</a>
</span>
</li>
<li itemscope itemtype="http://www.schema.org/SiteNavigationElement">
<span>
<a href="../../reference/numeric.html" itemprop="url">
<span itemprop="name">numeric</span>
</a>
</span>
</li>
<li class="active" itemscope itemtype="http://www.schema.org/SiteNavigationElement">
<span>
<span itemprop="name">reduce</span>
</span>
</li>
</ol>
<div class="crsearch"></div>
</div>
</div>
<div class="row">
<div class="col-sm-12 edit-button">
<p class="text-right"><small>
最終更新日時:
<time itemprop="datePublished" class="js-local-time"
datetime="2025-07-09T00:33:39+09:00">
2025年07月09日 00時33分39秒 (JST)
</time>
<br/>
<span itemprop="author" itemscope itemtype="http://schema.org/Person">
<span itemprop="name">Akira Takahashi</span>
</span>
が更新
</small></p>
<script>
(function () {
// 最終更新日時を閲覧者のローカルタイムゾーンで表示し直す (issue #53 の正規化)。
// JS が無効な環境ではサーバ生成の JST 表記がそのまま残る。
function pad(n) { return (n < 10 ? '0' : '') + n; }
var els = document.querySelectorAll('time.js-local-time[datetime]');
for (var i = 0; i < els.length; i++) {
var el = els[i];
var d = new Date(el.getAttribute('datetime'));
if (isNaN(d.getTime())) { continue; }
var tz = '';
try {
var parts = new Intl.DateTimeFormat(undefined, { timeZoneName: 'short' }).formatToParts(d);
for (var j = 0; j < parts.length; j++) {
if (parts[j].type === 'timeZoneName') { tz = parts[j].value; break; }
}
} catch (e) {}
el.textContent = d.getFullYear() + '年' + pad(d.getMonth() + 1) + '月' + pad(d.getDate()) + '日 '
+ pad(d.getHours()) + '時' + pad(d.getMinutes()) + '分' + pad(d.getSeconds()) + '秒'
+ (tz ? ' (' + tz + ')' : '');
}
})();
</script>
<p class="text-right">
<a class="history" target="_blank" href="https://github.com/cpprefjp/site/commits/master/reference/numeric/reduce.md">
<span class="fa fa-fw fa-clock-o fa-flip-horizontal"></span>履歴
</a>
<a class="edit" target="_blank" href="https://github.com/cpprefjp/site/edit/master/reference/numeric/reduce.md">
<span class="fa fa-fw fa-pencil"></span>編集
</a>
</p>
</div>
</div>
<div class="row">
<div class="col-sm-12 content-body">
<div class="identifier-type">function template</div><div class="header"><numeric></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">reduce</span><span class="cpp cpp17" title="C++17で追加">(C++17)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">InputIterator</span><span class="o">></span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="../iterator/iterator_traits.html">iterator_traits</a></span><span class="o"><</span><span class="n">InputIterator</span><span class="o">>::</span><span class="n">value_type</span>
<span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++17</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">InputIterator</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="../iterator/iterator_traits.html">iterator_traits</a></span><span class="o"><</span><span class="n">InputIterator</span><span class="o">>::</span><span class="n">value_type</span>
<span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">);</span><span class="w"> </span><span class="c1">// (1) C++20</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">InputIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">init</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++17</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">InputIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n">T</span>
<span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">init</span><span class="p">);</span><span class="w"> </span><span class="c1">// (2) C++20</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">InputIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">BinaryOperation</span><span class="o">></span>
<span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">init</span><span class="p">,</span>
<span class="w"> </span><span class="n">BinaryOperation</span><span class="w"> </span><span class="n">binary_op</span><span class="p">);</span><span class="w"> </span><span class="c1">// (3) C++17</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">InputIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">BinaryOperation</span><span class="o">></span>
<span class="w"> </span><span class="k">constexpr</span><span class="w"> </span><span class="n">T</span>
<span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n">InputIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">InputIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">init</span><span class="p">,</span>
<span class="w"> </span><span class="n">BinaryOperation</span><span class="w"> </span><span class="n">binary_op</span><span class="p">);</span><span class="w"> </span><span class="c1">// (3) C++20</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">ForwardIterator</span><span class="o">></span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="../iterator/iterator_traits.html">iterator_traits</a></span><span class="o"><</span><span class="n">ForwardIterator</span><span class="o">>::</span><span class="n">value_type</span>
<span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="o">&&</span><span class="w"> </span><span class="n">exec</span><span class="p">,</span>
<span class="w"> </span><span class="n">ForwardIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">ForwardIterator</span><span class="w"> </span><span class="n">last</span><span class="p">);</span><span class="w"> </span><span class="c1">// (4) C++17</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">ForwardIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="o">&&</span><span class="w"> </span><span class="n">exec</span><span class="p">,</span>
<span class="w"> </span><span class="n">ForwardIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">ForwardIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">init</span><span class="p">);</span><span class="w"> </span><span class="c1">// (5) C++17</span>
<span class="w"> </span><span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">ForwardIterator</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">BinaryOperation</span><span class="o">></span>
<span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="o">&&</span><span class="w"> </span><span class="n">exec</span><span class="p">,</span>
<span class="w"> </span><span class="n">ForwardIterator</span><span class="w"> </span><span class="n">first</span><span class="p">,</span>
<span class="w"> </span><span class="n">ForwardIterator</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="n">init</span><span class="p">,</span>
<span class="w"> </span><span class="n">BinaryOperation</span><span class="w"> </span><span class="n">binary_op</span><span class="p">);</span><span class="w"> </span><span class="c1">// (6) C++17</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p><code>reduce()</code>は、<a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[first, last)</code>を集計する関数である。<code><a href="accumulate.html">accumulate()</a></code>関数は範囲の先頭から順に要素を集計するが、この関数は並列計算のために集計順を規定しない。</p>
<p>初期値(<code>init</code>)と<a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[first, last)</code>を合算したリストの任意の組み合わせに、順不同で<code>binary_op(binary_op(a, b), binary_op(c, d))</code>のように適用していき、集計値を計算する。</p>
<ul>
<li>(1) : 集計の初期値を<a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a>の要素型の<a class="cpprefjp-defined-word" data-desc="`T x{};`構文での初期化。組み込み型の場合はゼロ相当の値で、クラス型の場合はデフォルトコンストラクタで初期化する。配列型の場合は各要素が再帰的に値初期化される">値初期化</a>値 (算術型なら<code>0</code>) とし、二項演算に<code>operator+</code>を使用する。それによって、この<a class="cpprefjp-defined-word" data-desc="同名の関数を異なる引数・テンプレート・制約などで複数定義すること。または同名の関数の集合">オーバーロード</a>は、範囲の合計値を求める処理となる</li>
<li>(2) : 初期値をパラメータ<code>init</code>として受け取り、二項演算は<code>operator+</code>を使用する</li>
<li>(3) : 初期値をパラメータ<code>init</code>として受け取り、任意の二項演算<code>binary_op</code>を使用して集計を行う</li>
<li>(4) : (1)の並列アルゴリズム版。第1パラメータとして実行ポリシーをとる</li>
<li>(5) : (2)の並列アルゴリズム版。第1パラメータとして実行ポリシーをとる</li>
<li>(6) : (3)の並列アルゴリズム版。第1パラメータとして実行ポリシーをとる</li>
</ul>
<h2>要件</h2>
<ul>
<li>(3), (6) : 関数オブジェクト<code>binary_op</code>の呼び出しは、<a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[first, last]</code>の要素変更およびイテレータの無効化をしてはならない</li>
</ul>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Constraints。関数であればオーバーロード解決に参加するための条件、それ以外であれば受け付ける型の条件">テンプレートパラメータ制約</a></h2>
<ul>
<li>(2), (3), (5), (6) : 型<code>T</code>が<code><a href="../concepts/move_constructible.html">std::move_constructible</a></code>要件を満たすこと</li>
<li>(3), (6) : 以下の全ての演算結果の型が、型<code>T</code>に変換可能であること<ul>
<li><code>binary_op(init, *first)</code></li>
<li><code>binary_op(*first, init)</code></li>
<li><code>binary_op(init, init)</code></li>
<li><code>binary_op(*first, *first)</code></li>
</ul>
</li>
</ul>
<h2>効果</h2>
<ul>
<li>
<p>(1) : 以下と等価
<br />
<div class="codehilite"><pre><span></span><code><span class="k">return</span><span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="../iterator/iterator_traits.html">iterator_traits</a></span><span class="o"><</span><span class="n">InputIterator</span><span class="o">>::</span><span class="n">value_type</span><span class="p">{});</span>
</code></pre></div>
</p>
</li>
<li>
<p>(2) : 以下と等価
<br />
<div class="codehilite"><pre><span></span><code><span class="k">return</span><span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">last</span><span class="p">,</span><span class="w"> </span><span class="n">init</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../functional/plus.html">plus</a></span><span class="o"><></span><span class="p">());</span>
</code></pre></div>
</p>
</li>
<li>
<p>(3), (6) : <a class="cpprefjp-defined-word" data-desc="2つのイテレータで表現される半開区間を表す。C++20からイテレータと番兵で異なる型であっても指定可能になる">イテレータ範囲</a><code>[first, last)</code>について、リスト<code>[init, *first, *(first + 1), *(first + 2), ... *(first + (last - first - 1))]</code>を任意の部分リストへ分割し、各部分リストの要素を順不同に<code>binary_op(a, b)</code>を実行していき、それを実行していった結果同士も順不同に<code>binary_op(sum1, sum2)</code>のように集計して返す</p>
</li>
<li>
<p>(4) : 以下と等価
<br />
<div class="codehilite"><pre><span></span><code><span class="k">return</span><span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n"><a href="../utility/forward.html">std::forward</a></span><span class="o"><</span><span class="n"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="o">></span><span class="p">(</span><span class="n">exec</span><span class="p">),</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">last</span><span class="p">,</span>
<span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc"><a href="../iterator/iterator_traits.html">iterator_traits</a></span><span class="o"><</span><span class="n">ForwardIterator</span><span class="o">>::</span><span class="n">value_type</span><span class="p">{});</span>
</code></pre></div>
</p>
</li>
<li>
<p>(5) : 以下と等価
<br />
<div class="codehilite"><pre><span></span><code><span class="k">return</span><span class="w"> </span><span class="n">reduce</span><span class="p">(</span><span class="n"><a href="../utility/forward.html">std::forward</a></span><span class="o"><</span><span class="n"><a href="../execution/execution/execution_policy.html">ExecutionPolicy</a></span><span class="o">></span><span class="p">(</span><span class="n">exec</span><span class="p">),</span><span class="w"> </span><span class="n">first</span><span class="p">,</span><span class="w"> </span><span class="n">last</span><span class="p">,</span><span class="w"> </span><span class="n">init</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../functional/plus.html">plus</a></span><span class="o"><></span><span class="p">());</span>
</code></pre></div>
</p>
</li>
</ul>
<h2><a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Complexity。関数が使うアルゴリズムの空間計算量・時間計算量">計算量</a></h2>
<p>関数オブジェクト<code>binary_op</code>をO(<code>last - first</code>)回だけ適用する</p>
<h2>例</h2>
<p><div class="yata" id="98aea963e1a0f224973f2193197038d13d5011d5"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../vector.html"><vector></a></span>
<span class="cp">#include <a href="../numeric.html"><numeric></a></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n"><a href="../vector/vector.html">std::vector</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">};</span>
<span class="w"> </span><span class="c1">// (1) : 合計値を求める</span>
<span class="w"> </span><span class="c1">// イテレータの要素型で集計される</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::reduce</span></span><span class="p">(</span><span class="n"><a href="../vector/vector/begin.html">v.begin()</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../vector/vector/end.html">v.end()</a></span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"sum : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">sum</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="c1">// (2) : 合計値をlong long型として求める</span>
<span class="w"> </span><span class="c1">// reduceの第3引数がlong long型のゼロを表す0LLになっていることに注意</span>
<span class="w"> </span><span class="c1">// reduceの戻り値型は、第3引数の型となるため、変数sum_llの型はlong long</span>
<span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">sum_ll</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::reduce</span></span><span class="p">(</span><span class="n"><a href="../vector/vector/begin.html">v.begin()</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../vector/vector/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="mf">0L</span><span class="n">L</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"sum_ll : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">sum_ll</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="w"> </span><span class="c1">// (3) : 任意の二項演算を行う</span>
<span class="w"> </span><span class="c1">// ここでは、初期値を1として、全ての要素を掛け合わせている</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">product</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::reduce</span></span><span class="p">(</span><span class="n"><a href="../vector/vector/begin.html">v.begin()</a></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../vector/vector/end.html">v.end()</a></span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="p">[](</span><span class="kt">int</span><span class="w"> </span><span class="n">acc</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">acc</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">i</span><span class="p">;</span>
<span class="w"> </span><span class="p">});</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"product : "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">product</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><pre><code>sum : 15
sum_ll : 15
product : 120
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++17</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: 5.0.0 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#gcc">GCC</a>:</li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: ??</li>
</ul>
<h2>関連項目</h2>
<ul>
<li><code><a href="accumulate.html">std::accumulate()</a></code></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0024r2.html" target="_blank">P0024R2 The Parallelism TS Should be Standardized</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0467r2.html" target="_blank">P0467R2 Iterator Concerns for Parallel Algorithms</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0574r1.html" target="_blank">P0574R1: Algorithm Complexity Constraints and Parallel Overloads</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1645r1.html" target="_blank">P1645R1 <code>constexpr</code> for <code><numeric></code> algorithms</a><ul>
<li>C++20で、並列バージョン以外の数値計算アルゴリズムが<code>constexpr</code>対応した</li>
</ul>
</li>
</ul></div>
</div>
</div>
</div>
<div id="sidebar" class="col-sm-3 col-sm-pull-9">
</div>
</div>
</div>
</main>
<footer class="footer navbar navbar-default">
<div class="container-fluid">
<p><small>
本サイトの情報は、
<a href="https://creativecommons.org/licenses/by/4.0/deed.ja" rel="nofollow">クリエイティブ・コモンズ 表示 4.0 非移植 ライセンス(CC BY)</a>
の下に提供されています。
</small></p>
</div>
</footer>
</body>
</html>