-
Notifications
You must be signed in to change notification settings - Fork 0
/
24b36a685319.html
457 lines (349 loc) · 34.6 KB
/
24b36a685319.html
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
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width">
<meta name="theme-color" content="#222">
<meta name="generator" content="Hexo 5.4.0">
<link rel="apple-touch-icon" sizes="180x180" href="/images/mylogo-128x128.png">
<link rel="icon" type="image/png" sizes="32x32" href="/images/mylogo-32x32.png">
<link rel="icon" type="image/png" sizes="16x16" href="/images/mylogo-16x16.png">
<link rel="mask-icon" href="/images/mylogo.svg" color="#222">
<link rel="stylesheet" href="/css/main.css">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@fortawesome/[email protected]/css/all.min.css" integrity="sha256-mUZM63G8m73Mcidfrv5E+Y61y7a12O5mW4ezU3bxqW4=" crossorigin="anonymous">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/animate.min.css" integrity="sha256-PR7ttpcvz8qrF57fur/yAx1qXMFJeJFiA6pSzWi0OIE=" crossorigin="anonymous">
<script class="next-config" data-name="main" type="application/json">{"hostname":"renshengjihe.cn","root":"/","images":"/images","scheme":"Gemini","darkmode":false,"version":"8.8.0","exturl":false,"sidebar":{"position":"left","display":"post","padding":18,"offset":12},"copycode":"ture","bookmark":{"enable":false,"color":"#222","save":"auto"},"mediumzoom":false,"lazyload":false,"pangu":false,"comments":{"style":"tabs","active":null,"storage":true,"lazyload":false,"nav":null},"stickytabs":false,"motion":{"enable":true,"async":true,"transition":{"post_block":"fadeIn","post_header":"fadeInDown","post_body":"fadeInDown","coll_header":"fadeInLeft","sidebar":"fadeInUp"}},"prism":false,"i18n":{"placeholder":"搜索...","empty":"没有找到任何搜索结果：${query}","hits_time":"找到 ${hits} 个搜索结果（用时 ${time} 毫秒）","hits":"找到 ${hits} 个搜索结果"}}</script><script src="/js/config.js"></script>
<meta name="description" content="本文总结了 C/C++ 中动态内存分配的方法，malloc \ free \ calloc 函数的用法，new delete 的用法及其与 C 语言中函数的区别，operator new \ placement new \ operator delete 的原理与使用">
<meta property="og:type" content="article">
<meta property="og:title" content="C/C++动态内存管理">
<meta property="og:url" content="https://renshengjihe.cn/24b36a685319">
<meta property="og:site_name" content="人生几何">
<meta property="og:description" content="本文总结了 C/C++ 中动态内存分配的方法，malloc \ free \ calloc 函数的用法，new delete 的用法及其与 C 语言中函数的区别，operator new \ placement new \ operator delete 的原理与使用">
<meta property="og:locale" content="zh_CN">
<meta property="article:published_time" content="2019-08-04T01:57:23.000Z">
<meta property="article:modified_time" content="2021-10-22T16:44:27.989Z">
<meta property="article:author" content="dhd">
<meta property="article:tag" content="C/C++">
<meta name="twitter:card" content="summary">
<link rel="canonical" href="https://renshengjihe.cn/24b36a685319.html">
<script class="next-config" data-name="page" type="application/json">{"sidebar":"","isHome":false,"isPost":true,"lang":"zh-CN","comments":true,"permalink":"https://renshengjihe.cn/24b36a685319","path":"24b36a685319.html","title":"C/C++动态内存管理"}</script>
<script class="next-config" data-name="calendar" type="application/json">""</script>
<title>C/C++动态内存管理 | 人生几何</title>
<noscript>
<link rel="stylesheet" href="/css/noscript.css">
</noscript>
<!-- hexo injector head_end start -->
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/katex.min.css">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/style.css">
<!-- hexo injector head_end end --></head>
<body itemscope itemtype="http://schema.org/WebPage" class="use-motion">
<div class="headband"></div>
<main class="main">
<header class="header" itemscope itemtype="http://schema.org/WPHeader">
<div class="header-inner"><div class="site-brand-container">
<div class="site-nav-toggle">
<div class="toggle" aria-label="切换导航栏" role="button">
<span class="toggle-line"></span>
<span class="toggle-line"></span>
<span class="toggle-line"></span>
</div>
</div>
<div class="site-meta">
<a href="/" class="brand" rel="start">
<i class="logo-line"></i>
<h1 class="site-title">人生几何</h1>
<i class="logo-line"></i>
</a>
<p class="site-subtitle" itemprop="description">一个普通程序员的技术博客</p>
</div>
<div class="site-nav-right">
<div class="toggle popup-trigger">
</div>
</div>
</div>
<nav class="site-nav">
<ul class="main-menu menu">
<li class="menu-item menu-item-home"><a href="/" rel="section"><i class="fa fa-home fa-fw"></i>首页</a></li>
<li class="menu-item menu-item-tags"><a href="/tags/" rel="section"><i class="fa fa-tags fa-fw"></i>标签</a></li>
<li class="menu-item menu-item-categories"><a href="/categories/" rel="section"><i class="fa fa-th fa-fw"></i>分类</a></li>
<li class="menu-item menu-item-archives"><a href="/archives/" rel="section"><i class="fa fa-archive fa-fw"></i>归档</a></li>
</ul>
</nav>
</div>
<div class="toggle sidebar-toggle" role="button">
<span class="toggle-line"></span>
<span class="toggle-line"></span>
<span class="toggle-line"></span>
</div>
<aside class="sidebar">
<div class="sidebar-inner sidebar-nav-active sidebar-toc-active">
<ul class="sidebar-nav">
<li class="sidebar-nav-toc">
文章目录
</li>
<li class="sidebar-nav-overview">
站点概览
</li>
</ul>
<div class="sidebar-panel-container">
<!--noindex-->
<div class="post-toc-wrap sidebar-panel">
<div class="post-toc animated"><ol class="nav"><li class="nav-item nav-level-2"><a class="nav-link" href="#malloc-free-calloc-realloc"><span class="nav-number">1.</span> <span class="nav-text">malloc \ free \ calloc \ realloc</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#malloc"><span class="nav-number">1.1.</span> <span class="nav-text">malloc</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#free"><span class="nav-number">1.2.</span> <span class="nav-text">free</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#calloc"><span class="nav-number">1.3.</span> <span class="nav-text">calloc</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#realloc"><span class="nav-number">1.4.</span> <span class="nav-text">realloc</span></a></li></ol></li><li class="nav-item nav-level-2"><a class="nav-link" href="#new-delete"><span class="nav-number">2.</span> <span class="nav-text">new \ delete</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#%E4%B8%A4%E7%A7%8D%E6%96%B9%E5%BC%8F%E7%9A%84%E5%8C%BA%E5%88%AB"><span class="nav-number">3.</span> <span class="nav-text">两种方式的区别</span></a></li><li class="nav-item nav-level-2"><a class="nav-link" href="#operator-new-placement-new-operator-delete"><span class="nav-number">4.</span> <span class="nav-text">operator new \ placement new \ operator delete</span></a><ol class="nav-child"><li class="nav-item nav-level-3"><a class="nav-link" href="#operator-new"><span class="nav-number">4.1.</span> <span class="nav-text">operator new</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#placement-new"><span class="nav-number">4.2.</span> <span class="nav-text">placement new</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#operator-delete"><span class="nav-number">4.3.</span> <span class="nav-text">operator delete</span></a></li></ol></li></ol></div>
</div>
<!--/noindex-->
<div class="site-overview-wrap sidebar-panel">
<div class="site-author site-overview-item animated" itemprop="author" itemscope itemtype="http://schema.org/Person">
<img class="site-author-image" itemprop="image" alt="dhd"
src="/images/avatar.png">
<p class="site-author-name" itemprop="name">dhd</p>
<div class="site-description" itemprop="description">个人博客，分享一些C/C++ Linux 嵌入式等有趣的技术</div>
</div>
<div class="site-state-wrap site-overview-item animated">
<nav class="site-state">
<div class="site-state-item site-state-posts">
<a href="/archives/">
<span class="site-state-item-count">23</span>
<span class="site-state-item-name">日志</span>
</a>
</div>
<div class="site-state-item site-state-categories">
<a href="/categories/">
<span class="site-state-item-count">12</span>
<span class="site-state-item-name">分类</span></a>
</div>
<div class="site-state-item site-state-tags">
<a href="/tags/">
<span class="site-state-item-count">13</span>
<span class="site-state-item-name">标签</span></a>
</div>
</nav>
</div>
<div class="links-of-author site-overview-item animated">
<span class="links-of-author-item">
<a href="https://github.com/MissYourSmile" title="GitHub → https://github.com/MissYourSmile" rel="noopener" target="_blank"><i class="fab fa-github fa-fw"></i>GitHub</a>
</span>
<span class="links-of-author-item">
<a href="mailto:[email protected]" title="E-Mail → mailto:[email protected]" rel="noopener" target="_blank"><i class="fa fa-envelope fa-fw"></i>E-Mail</a>
</span>
</div>
</div>
</div>
</div>
</aside>
<div class="sidebar-dimmer"></div>
</header>
<div class="back-to-top" role="button" aria-label="返回顶部">
<i class="fa fa-arrow-up"></i>
<span>0%</span>
</div>
<noscript>
<div class="noscript-warning">Theme NexT works best with JavaScript enabled</div>
</noscript>
<div class="main-inner post posts-expand">
<div class="post-block">
<article itemscope itemtype="http://schema.org/Article" class="post-content" lang="zh-CN">
<link itemprop="mainEntityOfPage" href="https://renshengjihe.cn/24b36a685319">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/avatar.png">
<meta itemprop="name" content="dhd">
<meta itemprop="description" content="个人博客，分享一些C/C++ Linux 嵌入式等有趣的技术">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="人生几何">
</span>
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
C/C++动态内存管理
</h1>
<div class="post-meta-container">
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">发表于</span>
<time title="创建时间：2019-08-04 09:57:23" itemprop="dateCreated datePublished" datetime="2019-08-04T09:57:23+08:00">2019-08-04</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar-check"></i>
</span>
<span class="post-meta-item-text">更新于</span>
<time title="修改时间：2021-10-23 00:44:27" itemprop="dateModified" datetime="2021-10-23T00:44:27+08:00">2021-10-23</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-folder"></i>
</span>
<span class="post-meta-item-text">分类于</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/C-C/" itemprop="url" rel="index"><span itemprop="name">C/C++</span></a>
</span>
</span>
</div>
<div class="post-description">本文总结了 C/C++ 中动态内存分配的方法，malloc \ free \ calloc 函数的用法，new delete 的用法及其与 C 语言中函数的区别，operator new \ placement new \ operator delete 的原理与使用</div>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<p>在 C 和 C++ 中，对于动态内存的管理是一个永恒的话题，C语言采用 x(x)alloc 和 free 来开辟和释放动态内存空间，不同的是，C++ 引入了 new 和 delete 操作符作为新的方式。这二者有什么区别呢？new \ delete 又有哪些高级用法，这些都将在下文一一列出。</p>
<h2 id="malloc-free-calloc-realloc"><a href="#malloc-free-calloc-realloc" class="headerlink" title="malloc \ free \ calloc \ realloc"></a>malloc \ free \ calloc \ realloc</h2><h3 id="malloc"><a href="#malloc" class="headerlink" title="malloc"></a>malloc</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span>* <span class="title">malloc</span><span class="params">(<span class="keyword">size_t</span> size)</span></span>;</span><br></pre></td></tr></table></figure>
<p>开辟一段 size 字节大小的内存空间，并将空间的首地址返回，如果 size 为 0 ,则返回空指针。</p>
<h3 id="free"><a href="#free" class="headerlink" title="free"></a>free</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">free</span><span class="params">(<span class="keyword">void</span>* p)</span></span>;</span><br></pre></td></tr></table></figure>
<p>释放一段指针指向的内存空间。</p>
<h3 id="calloc"><a href="#calloc" class="headerlink" title="calloc"></a>calloc</h3><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span>* <span class="title">calloc</span><span class="params">(<span class="keyword">size_t</span> nmemb, <span class="keyword">size_t</span> size)</span></span>;</span><br></pre></td></tr></table></figure>
<p>开辟一段连续的内存空间，它的大小为 nmemb * size 字节，并为每一块内存地址赋 0，它实际上依然调用了 malloc 只是在 malloc 的基础上进行了额外的操作。</p>
<h3 id="realloc"><a href="#realloc" class="headerlink" title="realloc"></a>realloc</h3><p>函数原型</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span>* <span class="title">realloc</span><span class="params">(<span class="keyword">void</span>* ptr, <span class="keyword">size_t</span> size)</span></span>;</span><br></pre></td></tr></table></figure>
<p>重新开辟一段内存空间，将传入的指针 ptr 所指地址的空间调整至 size 大小。如果 size 比原来的空间大，会在另一个地址处开辟一段新的空间，而 ptr 所指的空间被释放；否则，返回的地址仍然是原先的地址，只是合法空间的大小经过了调整。不过即使 realloc 可能返回与 ptr 相同的首地址，但大多数情况下仍然要以下面的方式来使用 realloc 从而避免多次释放的问题。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">int</span> *p = (<span class="keyword">int</span>*)<span class="built_in">malloc</span>(<span class="number">5</span>*<span class="keyword">sizeof</span>(<span class="keyword">int</span>));</span><br><span class="line"> p = <span class="built_in">realloc</span>(p, <span class="number">10</span>*<span class="keyword">sizeof</span>(<span class="keyword">int</span>)); <span class="comment">// 传入参数 p 的地址在 realloc 中已经被释放</span></span><br><span class="line"> <span class="built_in">free</span>(p);</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="new-delete"><a href="#new-delete" class="headerlink" title="new \ delete"></a>new \ delete</h2><p>new 和 delete 是 C++ 中新增的动态内存管理的两个运算符，下面是 new 和 delete 的用例。</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">int</span> *p1 = <span class="keyword">new</span> <span class="built_in"><span class="keyword">int</span></span>(<span class="number">0</span>); <span class="comment">// 一个整形空间，初始化为 0</span></span><br><span class="line"> <span class="keyword">int</span> *p2 = <span class="keyword">new</span> <span class="keyword">int</span>[<span class="number">5</span>]; <span class="comment">// 五个整形空间</span></span><br><span class="line"> <span class="keyword">delete</span> p1; <span class="comment">// 释放单个空间</span></span><br><span class="line"> <span class="keyword">delete</span>[] p2; <span class="comment">// 释放连续空间</span></span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="两种方式的区别"><a href="#两种方式的区别" class="headerlink" title="两种方式的区别"></a>两种方式的区别</h2><p>下表总结了两种方式之间的区别</p>
<table>
<thead>
<tr>
<th align="right">特征</th>
<th align="left">new \ delete</th>
<th align="left">malloc \ free</th>
<th align="left">解释</th>
</tr>
</thead>
<tbody><tr>
<td align="right">分配内存的位置</td>
<td align="left">自由存储区</td>
<td align="left">堆区</td>
<td align="left">new 和 delete 可以重载，分配到那个存储区取决于具体实现。</td>
</tr>
<tr>
<td align="right">返回指针的类型</td>
<td align="left">完整的类型</td>
<td align="left">void*</td>
<td align="left">new 开辟出的内存空间不用像 malloc 那样做类型转换，使用起来更方便</td>
</tr>
<tr>
<td align="right">分配失败的处理</td>
<td align="left">抛出异常</td>
<td align="left">返回NULL</td>
<td align="left">抛出异常处理起来更加灵活</td>
</tr>
<tr>
<td align="right">分配内存的大小</td>
<td align="left">由编译器根据类型计算</td>
<td align="left">必须显示指定字节数</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">处理连续空间</td>
<td align="left">new[]</td>
<td align="left">必须用户计算数组大小后进行分配</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">已分配内存的扩充</td>
<td align="left">无法直观地处理</td>
<td align="left">使用 realloc 完成</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">是否相互调用</td>
<td align="left">可以，取决于重载的实现</td>
<td align="left">不可调用 new 和 delete</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">分配内存时内存不足</td>
<td align="left">无法通过用户代码处理</td>
<td align="left">能够使用 realloc 函数或重新制定分配器</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">函数重载</td>
<td align="left">允许</td>
<td align="left">不允许</td>
<td align="left"></td>
</tr>
<tr>
<td align="right">构造与析构</td>
<td align="left">调用</td>
<td align="left">不调用</td>
<td align="left">new 和 delete 为对象开辟/释放空间时会调用对应的构造、析构函数，这在面向对象的程序中极为重要</td>
</tr>
</tbody></table>
<h2 id="operator-new-placement-new-operator-delete"><a href="#operator-new-placement-new-operator-delete" class="headerlink" title="operator new \ placement new \ operator delete"></a>operator new \ placement new \ operator delete</h2><p>上面我们说的 <code>new</code> 运算符是 <code>new operator</code> 而不是 <code>operator new</code></p>
<p>这两者的区别在于 <code>new operator</code> 的行为是不可以被改变的，它稳定地完成两个任务：</p>
<ol>
<li>分配内存（调用的是 <code>operator new</code>）</li>
<li>调用构造函数初始化</li>
</ol>
<p>同样 <code>delete operator</code> 也是一样的道理</p>
<p>所谓的重载 <code>new</code> 和 <code>delete</code> 其实重载的是 <code>operator new</code> 和 <code>operator delete</code> 而不是 <code>new operator</code> 和 <code>delete operator</code></p>
<h3 id="operator-new"><a href="#operator-new" class="headerlink" title="operator new"></a>operator new</h3><p>下面是几个 <code>operator new</code> 的原型（定义在 <code>new</code> 文件中）</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 普通 operator new 版本，如果内存开辟失败，会抛出异常</span></span><br><span class="line"><span class="function"><span class="keyword">void</span>* <span class="keyword">operator</span> <span class="title">new</span> <span class="params">(std::<span class="keyword">size_t</span> size)</span> <span class="title">throw</span> <span class="params">(std::bad_alloc)</span></span>; </span><br><span class="line"><span class="keyword">void</span>* <span class="keyword">operator</span> <span class="keyword">new</span>[] (std::<span class="keyword">size_t</span> size) <span class="built_in"><span class="keyword">throw</span></span> (std::bad_alloc); </span><br><span class="line"><span class="comment">// 第二个参数没有实际的传输数据，它的作用在于标识这个函数不会抛出异常</span></span><br><span class="line"><span class="function"><span class="keyword">void</span>* <span class="keyword">operator</span> <span class="title">new</span> <span class="params">(std::<span class="keyword">size_t</span> size, <span class="keyword">const</span> std::<span class="keyword">nothrow_t</span>& nothrow_constant)</span> <span class="title">throw</span><span class="params">()</span></span>; </span><br><span class="line"><span class="keyword">void</span>* <span class="keyword">operator</span> <span class="keyword">new</span>[] (std::<span class="keyword">size_t</span> size, <span class="keyword">const</span> std::<span class="keyword">nothrow_t</span>& nothrow_constant) <span class="built_in"><span class="keyword">throw</span></span>(); </span><br></pre></td></tr></table></figure>
<p>如果要使用第二个版本的 <code>operator new</code>，需要在使用 <code>new operator</code>时按下面的方式使用。</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">int</span> *p = <span class="built_in"><span class="keyword">new</span></span>(std::nothrow) <span class="built_in"><span class="keyword">int</span></span>(<span class="number">0</span>);</span><br><span class="line"> <span class="keyword">delete</span> p;</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>同样，我们可以自己重写或者重载 <code>operator new</code>，如下：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span>* <span class="keyword">operator</span> <span class="title">new</span><span class="params">(<span class="keyword">size_t</span> size, <span class="keyword">const</span> <span class="keyword">char</span>* str)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> cout << <span class="string">"operator new "</span> << str << endl;</span><br><span class="line"> <span class="keyword">return</span> <span class="built_in">malloc</span>(size);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">int</span>* p = <span class="built_in"><span class="keyword">new</span></span>(<span class="string">"hello"</span>) <span class="built_in"><span class="keyword">int</span></span>(<span class="number">3</span>);</span><br><span class="line"> <span class="keyword">delete</span> []p;</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>程序执行结果为：</p>
<blockquote>
<p>operator new hello ..</p>
</blockquote>
<h3 id="placement-new"><a href="#placement-new" class="headerlink" title="placement new"></a>placement new</h3><p>在 <code>new</code> 文件中，还定义了一个类型的 <code>operaotr new</code>，原型如下：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// Default placement versions of operator new.</span></span><br><span class="line"><span class="function"><span class="keyword">inline</span> <span class="keyword">void</span>* <span class="keyword">operator</span> <span class="title">new</span><span class="params">(std::<span class="keyword">size_t</span>, <span class="keyword">void</span>* __p)</span> _GLIBCXX_USE_NOEXCEPT</span></span><br><span class="line"><span class="function"></span>{ <span class="keyword">return</span> __p; }</span><br><span class="line"><span class="keyword">inline</span> <span class="keyword">void</span>* <span class="keyword">operator</span> <span class="keyword">new</span>[](std::<span class="keyword">size_t</span>, <span class="keyword">void</span>* __p) _GLIBCXX_USE_NOEXCEPT</span><br><span class="line">{ <span class="keyword">return</span> __p; }</span><br></pre></td></tr></table></figure>
<p>这便是 <code>placement new</code>，它的作用在于在一个已经分配的内存空间上构造一个对象，其语法如下：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">char</span> a[<span class="number">4</span>] = {<span class="number">1</span>, <span class="number">1</span>, <span class="number">0</span>, <span class="number">0</span>};</span><br><span class="line"> cout << hex << &a << dec << endl;</span><br><span class="line"> <span class="keyword">int</span> *p = <span class="built_in"><span class="keyword">new</span></span>(&a) <span class="keyword">int</span>;</span><br><span class="line"> cout << hex << p << dec << endl;</span><br><span class="line"> cout << *p << endl;</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>程序执行结果为：</p>
<blockquote>
<p>0x7ffd738daa24<br>0x7ffd738daa24<br>257</p>
</blockquote>
<h3 id="operator-delete"><a href="#operator-delete" class="headerlink" title="operator delete"></a>operator delete</h3><p>同样，<code>operator delete</code> 也可以像 <code>operator new</code> 那样进行重载操作，如下：</p>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="keyword">operator</span> <span class="title">delete</span><span class="params">(<span class="keyword">void</span>* ptr)</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> cout << <span class="string">"operator delete"</span> << endl;</span><br><span class="line"> <span class="built_in">free</span>(ptr);</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">()</span></span></span><br><span class="line"><span class="function"></span>{</span><br><span class="line"> <span class="keyword">int</span> *p = <span class="keyword">new</span> <span class="keyword">int</span>;</span><br><span class="line"> <span class="built_in"><span class="keyword">delete</span></span>(p);</span><br><span class="line"> <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>执行结果为：</p>
<blockquote>
<p>operator delete</p>
</blockquote>
</div>
<footer class="post-footer">
<div class="post-tags">
<a href="/tags/C-C/" rel="tag"># C/C++</a>
</div>
<div class="post-nav">
<div class="post-nav-item">
<a href="/186533953c0c" rel="prev" title="设计模式-装饰模式(Decorator)">
<i class="fa fa-chevron-left"></i> 设计模式-装饰模式(Decorator)
</a>
</div>
<div class="post-nav-item">
<a href="/64e7062a60ef" rel="next" title="设计模式-桥模式(Bridge)">
设计模式-桥模式(Bridge) <i class="fa fa-chevron-right"></i>
</a>
</div>
</div>
</footer>
</article>
</div>
<div class="comments gitalk-container"></div>
</div>
</main>
<footer class="footer">
<div class="footer-inner">
<div class="copyright">
©
<span itemprop="copyrightYear">2021</span>
<span class="with-love">
<i class="fa fa-heart"></i>
</span>
<span class="author" itemprop="copyrightHolder">dhd</span>
</div>
<div class="powered-by">由 <a href="https://hexo.io/" rel="noopener" target="_blank">Hexo</a> & <a href="https://theme-next.js.org/" rel="noopener" target="_blank">NexT.Gemini</a> 强力驱动
</div>
</div>
</footer>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/lib/anime.min.js" integrity="sha256-XL2inqUJaslATFnHdJOi9GfQ60on8Wx1C2H8DYiN1xY=" crossorigin="anonymous"></script>
<script src="/js/comments.js"></script><script src="/js/utils.js"></script><script src="/js/motion.js"></script><script src="/js/next-boot.js"></script>
<script class="next-config" data-name="enableMath" type="application/json">false</script><script class="next-config" data-name="mathjax" type="application/json">{"enable":true,"tags":"none","js":{"url":"https://cdn.jsdelivr.net/npm/[email protected]/es5/tex-mml-chtml.js","integrity":"sha256-r+3itOMtGGjap0x+10hu6jW/gZCzxHsoKrOd7gyRSGY="}}</script>
<script src="/js/third-party/math/mathjax.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/gitalk.css" integrity="sha256-AJnUHL7dBv6PGaeyPQJcgQPDjt/Hn/PvYZde1iqfp8U=" crossorigin="anonymous">
<script class="next-config" data-name="gitalk" type="application/json">{"enable":true,"github_id":"MissYourSmile","repo":"blog","client_id":"90df46a08046f5b73ae9","client_secret":"fa93eaa0abad10d0f79e056b45ba8a0212d37e0d","admin_user":"MissYourSmile","distraction_free_mode":true,"proxy":"https://cors-anywhere.azm.workers.dev/https://github.com/login/oauth/access_token","language":"zh-CN","js":{"url":"https://cdn.jsdelivr.net/npm/[email protected]/dist/gitalk.min.js","integrity":"sha256-Pmj85ojLaPOWwRtlMJwmezB/Qg8BzvJp5eTzvXaYAfA="},"path_md5":"7919f53b4d36b959257b0127373857d3"}</script>
<script src="/js/third-party/comments/gitalk.js"></script>
</body>
</html>