-
Notifications
You must be signed in to change notification settings - Fork 1
Expand file tree
/
Copy pathget.html
More file actions
470 lines (380 loc) · 35.9 KB
/
Copy pathget.html
File metadata and controls
470 lines (380 loc) · 35.9 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
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
<!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::future::get - 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,future,std,future,function,cpp11
">
<meta name="title" content="std::future::get - cpprefjp C++日本語リファレンス" />
<meta itemprop="name" content="std::future::get - cpprefjp C++日本語リファレンス" />
<meta property="og:title" content="std::future::get - cpprefjp C++日本語リファレンス" />
<meta property="og:url" content="https://cpprefjp.github.io/reference/future/future/get.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="結果を取得する" />
<meta name="twitter:card" content="summary" />
<meta name="twitter:title" content="std::future::get - cpprefjp C++日本語リファレンス" />
<meta name="twitter:url" content="https://cpprefjp.github.io/reference/future/future/get.html" />
<meta name="twitter:description" content="結果を取得する" />
<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": ["future"], "namespace": ["std"], "class": ["future"], "id-type": ["function"], "cpp": ["cpp11"]}, "sources": [{"id": "d37e2d51b490175d55a76550ecf82e31905dac9a", "source": "#include <iostream>\n#include <future>\n#include <thread>\n#include <utility>\n\nvoid calc(std::promise<int> p)\n{\n int sum = 0;\n for (int i = 0; i < 10; ++i) {\n sum += i + 1;\n }\n\n p.set_value(sum); // \u7d50\u679c\u5024\u3092\u66f8\u304d\u8fbc\u3080\n}\n\nint main()\n{\n std::promise<int> p;\n std::future<int> f = p.get_future();\n\n // \u5225\u30b9\u30ec\u30c3\u30c9\u3067\u8a08\u7b97\u3092\u884c\u3046\n std::thread t(calc, std::move(p));\n\n // calc()\u306b\u3088\u3063\u3066\u66f8\u304d\u8fbc\u307e\u308c\u305f\u7d50\u679c\u3092\u53d6\u5f97\n std::cout << f.get() << std::endl;\n\n t.join();\n}\n"}, {"id": "125523280eeb57b09ca1ba690c594575004edbc6", "source": "#include <iostream>\n#include <future>\n#include <thread>\n#include <utility>\n\nclass Calculator {\n int sum_ = 0;\n std::future<int&> async_calc;\n\npublic:\n void start()\n {\n std::promise<int&> p;\n async_calc = p.get_future();\n\n std::thread t(&Calculator::calc, this, std::move(p));\n t.detach();\n }\n\n int get()\n {\n return async_calc.get(); // \u7d50\u679c\u5024\u3078\u306e\u53c2\u7167\u3092\u53d6\u5f97\u3059\u308b\n }\n\n void calc(std::promise<int&> p)\n {\n int sum = 0;\n for (int i = 0; i < 10; ++i) {\n sum += i + 1;\n }\n\n sum_ = sum;\n p.set_value(sum_); // \u30e1\u30f3\u30d0\u5909\u6570\u3078\u306e\u53c2\u7167\u3092\u7d50\u679c\u5024\u3068\u3057\u3066\u66f8\u304d\u8fbc\u3080\n }\n};\n\nint main()\n{\n Calculator c;\n\n // \u975e\u540c\u671f\u306b\u8a08\u7b97\u3092\u958b\u59cb\u3059\u308b\n c.start();\n\n // \u8a08\u7b97\u7d50\u679c\u3092\u53d6\u5f97\u3059\u308b\n int result = c.get();\n\n std::cout << result << std::endl;\n}\n"}, {"id": "18adf08ad1a0c4a11a757ae98ecb1a8cf63af067", "source": "#include <iostream>\n#include <future>\n#include <thread>\n#include <utility>\n\nclass Calculator {\n int sum_ = 0;\n std::future<void> async_calc;\n\npublic:\n void start()\n {\n std::promise<void> p;\n async_calc = p.get_future();\n\n std::thread t(&Calculator::calc, this, std::move(p));\n t.detach();\n }\n\n int get()\n {\n async_calc.get(); // \u7d42\u4e86\u5f85\u6a5f\u306e\u307f\u3092\u884c\u3046\n return sum_;\n }\n\n void calc(std::promise<void> p)\n {\n int sum = 0;\n for (int i = 0; i < 10; ++i) {\n sum += i + 1;\n }\n\n // \u30e1\u30f3\u30d0\u5909\u6570\u3068\u3057\u3066\u7d50\u679c\u3092\u4fdd\u6301\u3057\u3001promise\u3067\u306f\u8a08\u7b97\u7d42\u4e86\u306e\u901a\u77e5\u306e\u307f\u884c\u3046\n sum_ = sum;\n p.set_value();\n }\n};\n\nint main()\n{\n Calculator c;\n\n // \u975e\u540c\u671f\u306b\u8a08\u7b97\u3092\u958b\u59cb\u3059\u308b\n c.start();\n\n // \u8a08\u7b97\u7d50\u679c\u3092\u53d6\u5f97\u3059\u308b\n int result = c.get();\n\n std::cout << result << std::endl;\n}\n"}], "page_id": ["reference", "future", "future", "get"]}">
<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/future.html" itemprop="url">
<span itemprop="name">future</span>
</a>
</span>
</li>
<li itemscope itemtype="http://www.schema.org/SiteNavigationElement">
<span>
<a href="../../../reference/future/future.html" itemprop="url">
<span itemprop="name">future</span>
</a>
</span>
</li>
<li class="active" itemscope itemtype="http://www.schema.org/SiteNavigationElement">
<span>
<span itemprop="name">get</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="2025-07-12T02:16:44+09:00">
2025年07月12日 02時16分44秒 (JST)
</time>
<br/>
<span itemprop="author" itemscope itemtype="http://schema.org/Person">
<span itemprop="name">Koichi Murase</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/future/future/get.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/future/future/get.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</div><div class="header"><future></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="class" title="class future">future::</span><span class="token">get</span><span class="cpp cpp11" title="C++11で追加">(C++11)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="n">R</span><span class="w"> </span><span class="nf">future::get</span><span class="p">();</span>
<span class="n">R</span><span class="o">&</span><span class="w"> </span><span class="n">future</span><span class="o"><</span><span class="n">R</span><span class="o">&>::</span><span class="n">get</span><span class="p">();</span>
<span class="kt">void</span><span class="w"> </span><span class="n">future</span><span class="o"><</span><span class="kt">void</span><span class="o">>::</span><span class="n">get</span><span class="p">();</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>結果を取得する</p>
<h2>効果</h2>
<p>共有状態が準備完了状態(<code><a href="../future_status.html">future_status::ready</a></code>)になるまで<code><a href="wait.html">wait()</a></code>で待機し、共有状態に格納されている値を取得する。</p>
<h2><a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a></h2>
<ul>
<li><code>future::get()</code> ： 共有状態に格納されている値<code>v</code>を<code><a href="../../utility/move.html">std::move</a>(v)</code>で返す。</li>
<li><code>future<R&>::get()</code> ： 共有状態に格納されている参照を返す。</li>
<li><code>future<void>::get()</code> ： 何も返さない。</li>
</ul>
<h2><a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a></h2>
<p>共有状態に<a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a>が格納されていた場合、格納されている<a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a>を送出する。</p>
<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。Preconditions。関数呼び出し時に満たされていると関数が想定する条件。満たさなければ未定義の動作。契約属性の`[[expects]]`に相当">事前条件</a></h2>
<ul>
<li><code><a href="valid.html">valid()</a> == true</code><ul>
<li>この条件を満たさなかった場合、処理系によっては<code><a href="../future_error.html">future_error</a></code><a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a>を投げることがある。</li>
</ul>
</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。Postconditions。関数を実行後に満たされている条件。契約属性の`[[ensures]]`に相当">事後条件</a></h2>
<p>この関数呼び出し後は共有状態が破棄され、<code><a href="valid.html">valid()</a> == false</code>となること。</p>
<p>つまりこの関数は1オブジェクトにつき1回しか呼び出せない。</p>
<h2>例</h2>
<p><div class="yata" id="d37e2d51b490175d55a76550ecf82e31905dac9a"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../../future.html"><future></a></span>
<span class="cp">#include <a href="../../thread.html"><thread></a></span>
<span class="cp">#include <a href="../../utility.html"><utility></a></span>
<span class="kt">void</span><span class="w"> </span><span class="nf">calc</span><span class="p">(</span><span class="n"><a href="../promise.html">std::promise</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">p</span><span class="p">)</span>
<span class="p">{</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="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="o">++</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">sum</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="n"><a href="../promise/set_value.html">p.set_value</a></span><span class="p">(</span><span class="n">sum</span><span class="p">);</span><span class="w"> </span><span class="c1">// 結果値を書き込む</span>
<span class="p">}</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="n"><a href="../promise.html">std::promise</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">p</span><span class="p">;</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">future</span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../promise/get_future.html">p.get_future()</a></span><span class="p">;</span>
<span class="w"> </span><span class="c1">// 別スレッドで計算を行う</span>
<span class="w"> </span><span class="n"><a href="../../thread/thread.html">std::thread</a></span><span class="w"> </span><span class="n">t</span><span class="p">(</span><span class="n">calc</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../../utility/move.html">std::move</a></span><span class="p">(</span><span class="n">p</span><span class="p">));</span>
<span class="w"> </span><span class="c1">// calc()によって書き込まれた結果を取得</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="n">f</span><span class="p">.</span><span class="n"><span style="color:#ff0000">get()</span></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="n"><a href="../../thread/thread/join.html">t.join()</a></span><span class="p">;</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p><div class="codehilite"><pre><span></span><code><span class="mi">55</span>
</code></pre></div>
</p>
<h2>例：<code>std::future<R&></code></h2>
<p><div class="yata" id="125523280eeb57b09ca1ba690c594575004edbc6"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../../future.html"><future></a></span>
<span class="cp">#include <a href="../../thread.html"><thread></a></span>
<span class="cp">#include <a href="../../utility.html"><utility></a></span>
<span class="k">class</span><span class="w"> </span><span class="nc">Calculator</span><span class="w"> </span><span class="p">{</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="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">future</span><span class="o"><</span><span class="kt">int</span><span class="o">&></span><span class="w"> </span><span class="n">async_calc</span><span class="p">;</span>
<span class="k">public</span><span class="o">:</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">start</span><span class="p">()</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">promise</span><span class="o"><</span><span class="kt">int</span><span class="o">&></span><span class="w"> </span><span class="n">p</span><span class="p">;</span>
<span class="w"> </span><span class="n">async_calc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">p</span><span class="p">.</span><span class="n">get_future</span><span class="p">();</span>
<span class="w"> </span><span class="n"><a href="../../thread/thread.html">std::thread</a></span><span class="w"> </span><span class="nf">t</span><span class="p">(</span><span class="o">&</span><span class="n">Calculator</span><span class="o">::</span><span class="n">calc</span><span class="p">,</span><span class="w"> </span><span class="k">this</span><span class="p">,</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">p</span><span class="p">));</span>
<span class="w"> </span><span class="n">t</span><span class="p">.</span><span class="n">detach</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n"><span style="color:#ff0000">get</span></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">async_calc</span><span class="p">.</span><span class="n"><span style="color:#ff0000">get</span></span><span class="p">();</span><span class="w"> </span><span class="c1">// 結果値への参照を取得する</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">calc</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">promise</span><span class="o"><</span><span class="kt">int</span><span class="o">&></span><span class="w"> </span><span class="n">p</span><span class="p">)</span>
<span class="w"> </span><span class="p">{</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="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="o">++</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">sum</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</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">sum</span><span class="p">;</span>
<span class="w"> </span><span class="n">p</span><span class="p">.</span><span class="n">set_value</span><span class="p">(</span><span class="n">sum_</span><span class="p">);</span><span class="w"> </span><span class="c1">// メンバ変数への参照を結果値として書き込む</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</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="n">Calculator</span><span class="w"> </span><span class="n">c</span><span class="p">;</span>
<span class="w"> </span><span class="c1">// 非同期に計算を開始する</span>
<span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n">start</span><span class="p">();</span>
<span class="w"> </span><span class="c1">// 計算結果を取得する</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n"><span style="color:#ff0000">get</span></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="n">result</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>55
</code></pre></p>
<h2>例：<code>std::future<void></code></h2>
<p><div class="yata" id="18adf08ad1a0c4a11a757ae98ecb1a8cf63af067"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../../future.html"><future></a></span>
<span class="cp">#include <a href="../../thread.html"><thread></a></span>
<span class="cp">#include <a href="../../utility.html"><utility></a></span>
<span class="k">class</span><span class="w"> </span><span class="nc">Calculator</span><span class="w"> </span><span class="p">{</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="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">future</span><span class="o"><</span><span class="kt">void</span><span class="o">></span><span class="w"> </span><span class="n">async_calc</span><span class="p">;</span>
<span class="k">public</span><span class="o">:</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">start</span><span class="p">()</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">promise</span><span class="o"><</span><span class="kt">void</span><span class="o">></span><span class="w"> </span><span class="n">p</span><span class="p">;</span>
<span class="w"> </span><span class="n">async_calc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">p</span><span class="p">.</span><span class="n">get_future</span><span class="p">();</span>
<span class="w"> </span><span class="n"><a href="../../thread/thread.html">std::thread</a></span><span class="w"> </span><span class="nf">t</span><span class="p">(</span><span class="o">&</span><span class="n">Calculator</span><span class="o">::</span><span class="n">calc</span><span class="p">,</span><span class="w"> </span><span class="k">this</span><span class="p">,</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">p</span><span class="p">));</span>
<span class="w"> </span><span class="n">t</span><span class="p">.</span><span class="n">detach</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n"><span style="color:#ff0000">get</span></span><span class="p">()</span>
<span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">async_calc</span><span class="p">.</span><span class="n"><span style="color:#ff0000">get</span></span><span class="p">();</span><span class="w"> </span><span class="c1">// 終了待機のみを行う</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">sum_</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">calc</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">promise</span><span class="o"><</span><span class="kt">void</span><span class="o">></span><span class="w"> </span><span class="n">p</span><span class="p">)</span>
<span class="w"> </span><span class="p">{</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="mi">0</span><span class="p">;</span>
<span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="o">++</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">sum</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="c1">// メンバ変数として結果を保持し、promiseでは計算終了の通知のみ行う</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">sum</span><span class="p">;</span>
<span class="w"> </span><span class="n">p</span><span class="p">.</span><span class="n">set_value</span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="p">};</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="n">Calculator</span><span class="w"> </span><span class="n">c</span><span class="p">;</span>
<span class="w"> </span><span class="c1">// 非同期に計算を開始する</span>
<span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n">start</span><span class="p">();</span>
<span class="w"> </span><span class="c1">// 計算結果を取得する</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">result</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n"><span style="color:#ff0000">get</span></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="n">result</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>55
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++11</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../../implementation.html#clang">Clang</a>: ??</li>
<li><a href="../../../implementation.html#gcc">GCC</a>: 4.7.0 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../../implementation.html#icc">ICC</a>: ??</li>
<li><a href="../../../implementation.html#visual_cpp">Visual C++</a>: 2012 <span aria-label="検証済" role="img" title="検証済">✅</span><ul>
<li>2012段階の<code>std::thread</code>クラスは、コンストラクタに引数をムーブで渡すことができない。そのため、<code>promise</code>オブジェクトはスレッド間の共有オブジェクトにする必要がある。(所有権が曖昧になるため、スタイルとしてはよくない)
<a href="https://connect.microsoft.com/VisualStudio/feedback/details/737812" target="_blank">#737812 - std::thread does not accept std::move</a></li>
</ul>
</li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#2096" target="_blank">LWG Issue 2096. Incorrect constraints of <code>future::get</code> in regard to <code>MoveAssignable</code></a><ul>
<li>C++14から、<code>future::get()</code>の<a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a>が変更された。C++11では「ムーブ代入可能ならムーブで返し、そうでなければコピーで返す」となっていたが、これは現実的ではない制約だった。</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>