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<title>unsafe.Sizeof, Alignof 和 Offsetof | Go编程语言</title>
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<div class="book" data-level="13.1" data-chapter-title="unsafe.Sizeof, Alignof 和 Offsetof" data-filepath="ch13/ch13-01.md" data-basepath=".." data-revision="Wed Dec 16 2015 10:54:29 GMT+0800 (中国标准时间)">
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<li class="chapter " data-level="0" data-path="index.html">
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前言
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<li class="chapter " data-level="0.1" data-path="ch0/ch0-01.html">
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<b>0.1.</b>
Go語言起源
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<li class="chapter " data-level="0.2" data-path="ch0/ch0-02.html">
<a href="../ch0/ch0-02.html">
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<b>0.2.</b>
Go語言項目
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<li class="chapter " data-level="0.3" data-path="ch0/ch0-03.html">
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<b>0.3.</b>
本書的組織
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<b>0.4.</b>
更多的信息
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<b>0.5.</b>
緻謝
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<li class="chapter " data-level="1" data-path="ch1/ch1.html">
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<b>1.</b>
入門
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<li class="chapter " data-level="1.1" data-path="ch1/ch1-01.html">
<a href="../ch1/ch1-01.html">
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<b>1.1.</b>
Hello, World
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<li class="chapter " data-level="1.2" data-path="ch1/ch1-02.html">
<a href="../ch1/ch1-02.html">
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<b>1.2.</b>
命令行參數
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<li class="chapter " data-level="1.3" data-path="ch1/ch1-03.html">
<a href="../ch1/ch1-03.html">
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<b>1.3.</b>
査找重復的行
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<li class="chapter " data-level="1.4" data-path="ch1/ch1-04.html">
<a href="../ch1/ch1-04.html">
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<b>1.4.</b>
GIF動畫
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<li class="chapter " data-level="1.5" data-path="ch1/ch1-05.html">
<a href="../ch1/ch1-05.html">
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<b>1.5.</b>
穫取URL
</a>
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<li class="chapter " data-level="1.6" data-path="ch1/ch1-06.html">
<a href="../ch1/ch1-06.html">
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<b>1.6.</b>
併髮穫取多個URL
</a>
</li>
<li class="chapter " data-level="1.7" data-path="ch1/ch1-07.html">
<a href="../ch1/ch1-07.html">
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<b>1.7.</b>
Web服務
</a>
</li>
<li class="chapter " data-level="1.8" data-path="ch1/ch1-08.html">
<a href="../ch1/ch1-08.html">
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<b>1.8.</b>
本章要點
</a>
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</ul>
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<li class="chapter " data-level="2" data-path="ch2/ch2.html">
<a href="../ch2/ch2.html">
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<b>2.</b>
程序結構
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<li class="chapter " data-level="2.1" data-path="ch2/ch2-01.html">
<a href="../ch2/ch2-01.html">
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<b>2.1.</b>
命名
</a>
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<li class="chapter " data-level="2.2" data-path="ch2/ch2-02.html">
<a href="../ch2/ch2-02.html">
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<b>2.2.</b>
聲明
</a>
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<li class="chapter " data-level="2.3" data-path="ch2/ch2-03.html">
<a href="../ch2/ch2-03.html">
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<b>2.3.</b>
變量
</a>
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<li class="chapter " data-level="2.4" data-path="ch2/ch2-04.html">
<a href="../ch2/ch2-04.html">
<i class="fa fa-check"></i>
<b>2.4.</b>
賦值
</a>
</li>
<li class="chapter " data-level="2.5" data-path="ch2/ch2-05.html">
<a href="../ch2/ch2-05.html">
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<b>2.5.</b>
類型
</a>
</li>
<li class="chapter " data-level="2.6" data-path="ch2/ch2-06.html">
<a href="../ch2/ch2-06.html">
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<b>2.6.</b>
包和文件
</a>
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<li class="chapter " data-level="2.7" data-path="ch2/ch2-07.html">
<a href="../ch2/ch2-07.html">
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<b>2.7.</b>
作用域
</a>
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</ul>
</li>
<li class="chapter " data-level="3" data-path="ch3/ch3.html">
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<b>3.</b>
基礎數據類型
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<li class="chapter " data-level="3.1" data-path="ch3/ch3-01.html">
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<b>3.1.</b>
整型
</a>
</li>
<li class="chapter " data-level="3.2" data-path="ch3/ch3-02.html">
<a href="../ch3/ch3-02.html">
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<b>3.2.</b>
浮點數
</a>
</li>
<li class="chapter " data-level="3.3" data-path="ch3/ch3-03.html">
<a href="../ch3/ch3-03.html">
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<b>3.3.</b>
復數
</a>
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<li class="chapter " data-level="3.4" data-path="ch3/ch3-04.html">
<a href="../ch3/ch3-04.html">
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<b>3.4.</b>
佈爾型
</a>
</li>
<li class="chapter " data-level="3.5" data-path="ch3/ch3-05.html">
<a href="../ch3/ch3-05.html">
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<b>3.5.</b>
字符串
</a>
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<li class="chapter " data-level="3.6" data-path="ch3/ch3-06.html">
<a href="../ch3/ch3-06.html">
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<b>3.6.</b>
常量
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="4" data-path="ch4/ch4.html">
<a href="../ch4/ch4.html">
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<b>4.</b>
復閤數據類型
</a>
<ul class="articles">
<li class="chapter " data-level="4.1" data-path="ch4/ch4-01.html">
<a href="../ch4/ch4-01.html">
<i class="fa fa-check"></i>
<b>4.1.</b>
數組
</a>
</li>
<li class="chapter " data-level="4.2" data-path="ch4/ch4-02.html">
<a href="../ch4/ch4-02.html">
<i class="fa fa-check"></i>
<b>4.2.</b>
切片
</a>
</li>
<li class="chapter " data-level="4.3" data-path="ch4/ch4-03.html">
<a href="../ch4/ch4-03.html">
<i class="fa fa-check"></i>
<b>4.3.</b>
字典
</a>
</li>
<li class="chapter " data-level="4.4" data-path="ch4/ch4-04.html">
<a href="../ch4/ch4-04.html">
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<b>4.4.</b>
結構體
</a>
</li>
<li class="chapter " data-level="4.5" data-path="ch4/ch4-05.html">
<a href="../ch4/ch4-05.html">
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<b>4.5.</b>
JSON
</a>
</li>
<li class="chapter " data-level="4.6" data-path="ch4/ch4-06.html">
<a href="../ch4/ch4-06.html">
<i class="fa fa-check"></i>
<b>4.6.</b>
文本和HTML模闆
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="5" data-path="ch5/ch5.html">
<a href="../ch5/ch5.html">
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<b>5.</b>
函數
</a>
<ul class="articles">
<li class="chapter " data-level="5.1" data-path="ch5/ch5-01.html">
<a href="../ch5/ch5-01.html">
<i class="fa fa-check"></i>
<b>5.1.</b>
函數聲明
</a>
</li>
<li class="chapter " data-level="5.2" data-path="ch5/ch5-02.html">
<a href="../ch5/ch5-02.html">
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<b>5.2.</b>
遞歸
</a>
</li>
<li class="chapter " data-level="5.3" data-path="ch5/ch5-03.html">
<a href="../ch5/ch5-03.html">
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<b>5.3.</b>
多返迴值
</a>
</li>
<li class="chapter " data-level="5.4" data-path="ch5/ch5-04.html">
<a href="../ch5/ch5-04.html">
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<b>5.4.</b>
錯誤
</a>
</li>
<li class="chapter " data-level="5.5" data-path="ch5/ch5-05.html">
<a href="../ch5/ch5-05.html">
<i class="fa fa-check"></i>
<b>5.5.</b>
函數值
</a>
</li>
<li class="chapter " data-level="5.6" data-path="ch5/ch5-06.html">
<a href="../ch5/ch5-06.html">
<i class="fa fa-check"></i>
<b>5.6.</b>
匿名函數
</a>
</li>
<li class="chapter " data-level="5.7" data-path="ch5/ch5-07.html">
<a href="../ch5/ch5-07.html">
<i class="fa fa-check"></i>
<b>5.7.</b>
可變參數
</a>
</li>
<li class="chapter " data-level="5.8" data-path="ch5/ch5-08.html">
<a href="../ch5/ch5-08.html">
<i class="fa fa-check"></i>
<b>5.8.</b>
Deferred函數
</a>
</li>
<li class="chapter " data-level="5.9" data-path="ch5/ch5-09.html">
<a href="../ch5/ch5-09.html">
<i class="fa fa-check"></i>
<b>5.9.</b>
Panic異常
</a>
</li>
<li class="chapter " data-level="5.10" data-path="ch5/ch5-10.html">
<a href="../ch5/ch5-10.html">
<i class="fa fa-check"></i>
<b>5.10.</b>
Recover捕穫異常
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="6" data-path="ch6/ch6.html">
<a href="../ch6/ch6.html">
<i class="fa fa-check"></i>
<b>6.</b>
方法
</a>
<ul class="articles">
<li class="chapter " data-level="6.1" data-path="ch6/ch6-01.html">
<a href="../ch6/ch6-01.html">
<i class="fa fa-check"></i>
<b>6.1.</b>
方法聲明
</a>
</li>
<li class="chapter " data-level="6.2" data-path="ch6/ch6-02.html">
<a href="../ch6/ch6-02.html">
<i class="fa fa-check"></i>
<b>6.2.</b>
基於指鍼對象的方法
</a>
</li>
<li class="chapter " data-level="6.3" data-path="ch6/ch6-03.html">
<a href="../ch6/ch6-03.html">
<i class="fa fa-check"></i>
<b>6.3.</b>
通過嵌入結構體來擴展類型
</a>
</li>
<li class="chapter " data-level="6.4" data-path="ch6/ch6-04.html">
<a href="../ch6/ch6-04.html">
<i class="fa fa-check"></i>
<b>6.4.</b>
方法值和方法錶達式
</a>
</li>
<li class="chapter " data-level="6.5" data-path="ch6/ch6-05.html">
<a href="../ch6/ch6-05.html">
<i class="fa fa-check"></i>
<b>6.5.</b>
示例: Bit數組
</a>
</li>
<li class="chapter " data-level="6.6" data-path="ch6/ch6-06.html">
<a href="../ch6/ch6-06.html">
<i class="fa fa-check"></i>
<b>6.6.</b>
封裝
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="7" data-path="ch7/ch7.html">
<a href="../ch7/ch7.html">
<i class="fa fa-check"></i>
<b>7.</b>
接口
</a>
<ul class="articles">
<li class="chapter " data-level="7.1" data-path="ch7/ch7-01.html">
<a href="../ch7/ch7-01.html">
<i class="fa fa-check"></i>
<b>7.1.</b>
接口是閤約
</a>
</li>
<li class="chapter " data-level="7.2" data-path="ch7/ch7-02.html">
<a href="../ch7/ch7-02.html">
<i class="fa fa-check"></i>
<b>7.2.</b>
接口類型
</a>
</li>
<li class="chapter " data-level="7.3" data-path="ch7/ch7-03.html">
<a href="../ch7/ch7-03.html">
<i class="fa fa-check"></i>
<b>7.3.</b>
實現接口的條件
</a>
</li>
<li class="chapter " data-level="7.4" data-path="ch7/ch7-04.html">
<a href="../ch7/ch7-04.html">
<i class="fa fa-check"></i>
<b>7.4.</b>
flag.Value接口
</a>
</li>
<li class="chapter " data-level="7.5" data-path="ch7/ch7-05.html">
<a href="../ch7/ch7-05.html">
<i class="fa fa-check"></i>
<b>7.5.</b>
接口值
</a>
</li>
<li class="chapter " data-level="7.6" data-path="ch7/ch7-06.html">
<a href="../ch7/ch7-06.html">
<i class="fa fa-check"></i>
<b>7.6.</b>
sort.Interface接口
</a>
</li>
<li class="chapter " data-level="7.7" data-path="ch7/ch7-07.html">
<a href="../ch7/ch7-07.html">
<i class="fa fa-check"></i>
<b>7.7.</b>
http.Handler接口
</a>
</li>
<li class="chapter " data-level="7.8" data-path="ch7/ch7-08.html">
<a href="../ch7/ch7-08.html">
<i class="fa fa-check"></i>
<b>7.8.</b>
error接口
</a>
</li>
<li class="chapter " data-level="7.9" data-path="ch7/ch7-09.html">
<a href="../ch7/ch7-09.html">
<i class="fa fa-check"></i>
<b>7.9.</b>
示例: 錶達式求值
</a>
</li>
<li class="chapter " data-level="7.10" data-path="ch7/ch7-10.html">
<a href="../ch7/ch7-10.html">
<i class="fa fa-check"></i>
<b>7.10.</b>
類型斷言
</a>
</li>
<li class="chapter " data-level="7.11" data-path="ch7/ch7-11.html">
<a href="../ch7/ch7-11.html">
<i class="fa fa-check"></i>
<b>7.11.</b>
基於類型斷言識彆錯誤類型
</a>
</li>
<li class="chapter " data-level="7.12" data-path="ch7/ch7-12.html">
<a href="../ch7/ch7-12.html">
<i class="fa fa-check"></i>
<b>7.12.</b>
通過類型斷言査詢接口
</a>
</li>
<li class="chapter " data-level="7.13" data-path="ch7/ch7-13.html">
<a href="../ch7/ch7-13.html">
<i class="fa fa-check"></i>
<b>7.13.</b>
類型分支
</a>
</li>
<li class="chapter " data-level="7.14" data-path="ch7/ch7-14.html">
<a href="../ch7/ch7-14.html">
<i class="fa fa-check"></i>
<b>7.14.</b>
示例: 基於標記的XML解碼
</a>
</li>
<li class="chapter " data-level="7.15" data-path="ch7/ch7-15.html">
<a href="../ch7/ch7-15.html">
<i class="fa fa-check"></i>
<b>7.15.</b>
補充幾點
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="8" data-path="ch8/ch8.html">
<a href="../ch8/ch8.html">
<i class="fa fa-check"></i>
<b>8.</b>
Goroutines和Channels
</a>
<ul class="articles">
<li class="chapter " data-level="8.1" data-path="ch8/ch8-01.html">
<a href="../ch8/ch8-01.html">
<i class="fa fa-check"></i>
<b>8.1.</b>
Goroutines
</a>
</li>
<li class="chapter " data-level="8.2" data-path="ch8/ch8-02.html">
<a href="../ch8/ch8-02.html">
<i class="fa fa-check"></i>
<b>8.2.</b>
示例: 併髮的Clock服務
</a>
</li>
<li class="chapter " data-level="8.3" data-path="ch8/ch8-03.html">
<a href="../ch8/ch8-03.html">
<i class="fa fa-check"></i>
<b>8.3.</b>
示例: 併髮的Echo服務
</a>
</li>
<li class="chapter " data-level="8.4" data-path="ch8/ch8-04.html">
<a href="../ch8/ch8-04.html">
<i class="fa fa-check"></i>
<b>8.4.</b>
Channels
</a>
</li>
<li class="chapter " data-level="8.5" data-path="ch8/ch8-05.html">
<a href="../ch8/ch8-05.html">
<i class="fa fa-check"></i>
<b>8.5.</b>
併行的循環
</a>
</li>
<li class="chapter " data-level="8.6" data-path="ch8/ch8-06.html">
<a href="../ch8/ch8-06.html">
<i class="fa fa-check"></i>
<b>8.6.</b>
示例: 併髮的Web爬蟲
</a>
</li>
<li class="chapter " data-level="8.7" data-path="ch8/ch8-07.html">
<a href="../ch8/ch8-07.html">
<i class="fa fa-check"></i>
<b>8.7.</b>
基於select的多路復用
</a>
</li>
<li class="chapter " data-level="8.8" data-path="ch8/ch8-08.html">
<a href="../ch8/ch8-08.html">
<i class="fa fa-check"></i>
<b>8.8.</b>
示例: 併髮的字典遍歷
</a>
</li>
<li class="chapter " data-level="8.9" data-path="ch8/ch8-09.html">
<a href="../ch8/ch8-09.html">
<i class="fa fa-check"></i>
<b>8.9.</b>
併髮的退齣
</a>
</li>
<li class="chapter " data-level="8.10" data-path="ch8/ch8-10.html">
<a href="../ch8/ch8-10.html">
<i class="fa fa-check"></i>
<b>8.10.</b>
示例: 聊天服務
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="9" data-path="ch9/ch9.html">
<a href="../ch9/ch9.html">
<i class="fa fa-check"></i>
<b>9.</b>
基於共享變量的併髮
</a>
<ul class="articles">
<li class="chapter " data-level="9.1" data-path="ch9/ch9-01.html">
<a href="../ch9/ch9-01.html">
<i class="fa fa-check"></i>
<b>9.1.</b>
競爭條件
</a>
</li>
<li class="chapter " data-level="9.2" data-path="ch9/ch9-02.html">
<a href="../ch9/ch9-02.html">
<i class="fa fa-check"></i>
<b>9.2.</b>
sync.Mutex互斥鎖
</a>
</li>
<li class="chapter " data-level="9.3" data-path="ch9/ch9-03.html">
<a href="../ch9/ch9-03.html">
<i class="fa fa-check"></i>
<b>9.3.</b>
sync.RWMutex讀寫鎖
</a>
</li>
<li class="chapter " data-level="9.4" data-path="ch9/ch9-04.html">
<a href="../ch9/ch9-04.html">
<i class="fa fa-check"></i>
<b>9.4.</b>
內存衕步
</a>
</li>
<li class="chapter " data-level="9.5" data-path="ch9/ch9-05.html">
<a href="../ch9/ch9-05.html">
<i class="fa fa-check"></i>
<b>9.5.</b>
sync.Once初始化
</a>
</li>
<li class="chapter " data-level="9.6" data-path="ch9/ch9-06.html">
<a href="../ch9/ch9-06.html">
<i class="fa fa-check"></i>
<b>9.6.</b>
競爭條件檢測
</a>
</li>
<li class="chapter " data-level="9.7" data-path="ch9/ch9-07.html">
<a href="../ch9/ch9-07.html">
<i class="fa fa-check"></i>
<b>9.7.</b>
示例: 併髮的非阻塞緩存
</a>
</li>
<li class="chapter " data-level="9.8" data-path="ch9/ch9-08.html">
<a href="../ch9/ch9-08.html">
<i class="fa fa-check"></i>
<b>9.8.</b>
Goroutines和綫程
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="10" data-path="ch10/ch10.html">
<a href="../ch10/ch10.html">
<i class="fa fa-check"></i>
<b>10.</b>
包和工具
</a>
<ul class="articles">
<li class="chapter " data-level="10.1" data-path="ch10/ch10-01.html">
<a href="../ch10/ch10-01.html">
<i class="fa fa-check"></i>
<b>10.1.</b>
簡介
</a>
</li>
<li class="chapter " data-level="10.2" data-path="ch10/ch10-02.html">
<a href="../ch10/ch10-02.html">
<i class="fa fa-check"></i>
<b>10.2.</b>
導入路徑
</a>
</li>
<li class="chapter " data-level="10.3" data-path="ch10/ch10-03.html">
<a href="../ch10/ch10-03.html">
<i class="fa fa-check"></i>
<b>10.3.</b>
包聲明
</a>
</li>
<li class="chapter " data-level="10.4" data-path="ch10/ch10-04.html">
<a href="../ch10/ch10-04.html">
<i class="fa fa-check"></i>
<b>10.4.</b>
導入聲明
</a>
</li>
<li class="chapter " data-level="10.5" data-path="ch10/ch10-05.html">
<a href="../ch10/ch10-05.html">
<i class="fa fa-check"></i>
<b>10.5.</b>
匿名導入
</a>
</li>
<li class="chapter " data-level="10.6" data-path="ch10/ch10-06.html">
<a href="../ch10/ch10-06.html">
<i class="fa fa-check"></i>
<b>10.6.</b>
包和命名
</a>
</li>
<li class="chapter " data-level="10.7" data-path="ch10/ch10-07.html">
<a href="../ch10/ch10-07.html">
<i class="fa fa-check"></i>
<b>10.7.</b>
工具
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="11" data-path="ch11/ch11.html">
<a href="../ch11/ch11.html">
<i class="fa fa-check"></i>
<b>11.</b>
測試
</a>
<ul class="articles">
<li class="chapter " data-level="11.1" data-path="ch11/ch11-01.html">
<a href="../ch11/ch11-01.html">
<i class="fa fa-check"></i>
<b>11.1.</b>
go test
</a>
</li>
<li class="chapter " data-level="11.2" data-path="ch11/ch11-02.html">
<a href="../ch11/ch11-02.html">
<i class="fa fa-check"></i>
<b>11.2.</b>
測試函數
</a>
</li>
<li class="chapter " data-level="11.3" data-path="ch11/ch11-03.html">
<a href="../ch11/ch11-03.html">
<i class="fa fa-check"></i>
<b>11.3.</b>
測試覆蓋率
</a>
</li>
<li class="chapter " data-level="11.4" data-path="ch11/ch11-04.html">
<a href="../ch11/ch11-04.html">
<i class="fa fa-check"></i>
<b>11.4.</b>
基準測試
</a>
</li>
<li class="chapter " data-level="11.5" data-path="ch11/ch11-05.html">
<a href="../ch11/ch11-05.html">
<i class="fa fa-check"></i>
<b>11.5.</b>
剖析
</a>
</li>
<li class="chapter " data-level="11.6" data-path="ch11/ch11-06.html">
<a href="../ch11/ch11-06.html">
<i class="fa fa-check"></i>
<b>11.6.</b>
示例函數
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="12" data-path="ch12/ch12.html">
<a href="../ch12/ch12.html">
<i class="fa fa-check"></i>
<b>12.</b>
反射
</a>
<ul class="articles">
<li class="chapter " data-level="12.1" data-path="ch12/ch12-01.html">
<a href="../ch12/ch12-01.html">
<i class="fa fa-check"></i>
<b>12.1.</b>
為何需要反射?
</a>
</li>
<li class="chapter " data-level="12.2" data-path="ch12/ch12-02.html">
<a href="../ch12/ch12-02.html">
<i class="fa fa-check"></i>
<b>12.2.</b>
reflect.Type和reflect.Value
</a>
</li>
<li class="chapter " data-level="12.3" data-path="ch12/ch12-03.html">
<a href="../ch12/ch12-03.html">
<i class="fa fa-check"></i>
<b>12.3.</b>
Display遞歸打印
</a>
</li>
<li class="chapter " data-level="12.4" data-path="ch12/ch12-04.html">
<a href="../ch12/ch12-04.html">
<i class="fa fa-check"></i>
<b>12.4.</b>
示例: 編碼S錶達式
</a>
</li>
<li class="chapter " data-level="12.5" data-path="ch12/ch12-05.html">
<a href="../ch12/ch12-05.html">
<i class="fa fa-check"></i>
<b>12.5.</b>
通過reflect.Value脩改值
</a>
</li>
<li class="chapter " data-level="12.6" data-path="ch12/ch12-06.html">
<a href="../ch12/ch12-06.html">
<i class="fa fa-check"></i>
<b>12.6.</b>
示例: 解碼S錶達式
</a>
</li>
<li class="chapter " data-level="12.7" data-path="ch12/ch12-07.html">
<a href="../ch12/ch12-07.html">
<i class="fa fa-check"></i>
<b>12.7.</b>
穫取結構體字段標識
</a>
</li>
<li class="chapter " data-level="12.8" data-path="ch12/ch12-08.html">
<a href="../ch12/ch12-08.html">
<i class="fa fa-check"></i>
<b>12.8.</b>
顯示一個類型的方法集
</a>
</li>
<li class="chapter " data-level="12.9" data-path="ch12/ch12-09.html">
<a href="../ch12/ch12-09.html">
<i class="fa fa-check"></i>
<b>12.9.</b>
幾點忠告
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="13" data-path="ch13/ch13.html">
<a href="../ch13/ch13.html">
<i class="fa fa-check"></i>
<b>13.</b>
底層編程
</a>
<ul class="articles">
<li class="chapter active" data-level="13.1" data-path="ch13/ch13-01.html">
<a href="../ch13/ch13-01.html">
<i class="fa fa-check"></i>
<b>13.1.</b>
unsafe.Sizeof, Alignof 和 Offsetof
</a>
</li>
<li class="chapter " data-level="13.2" data-path="ch13/ch13-02.html">
<a href="../ch13/ch13-02.html">
<i class="fa fa-check"></i>
<b>13.2.</b>
unsafe.Pointer
</a>
</li>
<li class="chapter " data-level="13.3" data-path="ch13/ch13-03.html">
<a href="../ch13/ch13-03.html">
<i class="fa fa-check"></i>
<b>13.3.</b>
示例: 深度相等判斷
</a>
</li>
<li class="chapter " data-level="13.4" data-path="ch13/ch13-04.html">
<a href="../ch13/ch13-04.html">
<i class="fa fa-check"></i>
<b>13.4.</b>
通過cgo調用C代碼
</a>
</li>
<li class="chapter " data-level="13.5" data-path="ch13/ch13-05.html">
<a href="../ch13/ch13-05.html">
<i class="fa fa-check"></i>
<b>13.5.</b>
幾點忠告
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="14" data-path="exercise/ex.html">
<a href="../exercise/ex.html">
<i class="fa fa-check"></i>
<b>14.</b>
習題解答
</a>
<ul class="articles">
<li class="chapter " data-level="14.1" data-path="exercise/ex-ch1.html">
<a href="../exercise/ex-ch1.html">
<i class="fa fa-check"></i>
<b>14.1.</b>
第一章 入門
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="15" data-path="errata.html">
<a href="../errata.html">
<i class="fa fa-check"></i>
<b>15.</b>
勘誤
</a>
</li>
<li class="divider"></li>
<li>
<a href="https://www.gitbook.com" target="blank" class="gitbook-link">
本書使用 GitBook 釋出
</a>
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<h2 id="131-unsafesizeof-alignof-&#x548C;-offsetof">13.1. unsafe.Sizeof, Alignof &#x548C; Offsetof</h2>
<p><code>unsafe.Sizeof</code> &#x51FD;&#x6578;&#x8FD4;&#x8FF4;&#x64CD;&#x4F5C;&#x6578;&#x5728;&#x5167;&#x5B58;&#x7684;&#x5B57;&#x7BC0;&#x5927;&#x5C0F;, &#x53EF;&#x4EE5;&#x662F;&#x4EFB;&#x610F;&#x985E;&#x578B;&#x7684;&#x9336;&#x9054;&#x5F0F;, &#x4F46;&#x662F;&#x4F75;&#x4E0D;&#x6703;&#x5C0D;&#x9336;&#x9054;&#x5F0F;&#x9032;&#x884C;&#x6C42;&#x503C;. <code>Sizeof</code> &#x662F;&#x4E00;&#x500B; uintptr &#x985E;&#x578B;&#x7684;&#x5E38;&#x91CF;&#x9336;&#x9054;&#x5F0F;, &#x56E0;&#x6B64;&#x8FD4;&#x8FF4;&#x7684;&#x7D50;&#x679C;&#x53EF;&#x4EE5;&#x7528;&#x7740;&#x6578;&#x64DA;&#x7684;&#x5927;&#x5C0F;, &#x6216;&#x8005;&#x7528;&#x4F5C;&#x8A08;&#x7B97;&#x5176;&#x4ED6;&#x7684;&#x5E38;&#x91CF;.</p>
<pre><code class="lang-Go"><span class="hljs-keyword">import</span> <span class="hljs-string">&quot;unsafe&quot;</span>
fmt.Println(unsafe.Sizeof(<span class="hljs-typename">float64</span>(<span class="hljs-number">0</span>))) <span class="hljs-comment">// &quot;8&quot;</span>
</code></pre>
<p><code>Sizeof</code> &#x96BB;&#x8FD4;&#x8FF4;&#x6578;&#x64DA;&#x7D50;&#x69CB;&#x4E2D;&#x56FA;&#x5B9A;&#x7684;&#x90E8;&#x5206;, &#x4F8B;&#x5982;&#x5B57;&#x7B26;&#x4E32;&#x4E2D;&#x6307;&#x937C;&#x548C;&#x5B57;&#x7B26;&#x4E32;&#x9577;&#x5EA6;&#x90E8;&#x5206;, &#x4F46;&#x662F;&#x4F75;&#x4E0D;&#x5305;&#x542B;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x5167;&#x5BB9;. Go&#x4E2D;&#x975E;&#x805A;&#x95A4;&#x985E;&#x578B;&#x901A;&#x5E38;&#x6709;&#x4E00;&#x500B;&#x56FA;&#x5B9A;&#x7684;&#x5C3A;&#x5BF8;, &#x76E1;&#x7BA1;&#x4E0D;&#x8855;&#x5DE5;&#x5177;&#x93C8;&#x7684;&#x5177;&#x9AD4;&#x5927;&#x5C0F;&#x53EF;&#x80FD;&#x6703;&#x6709;&#x6240;&#x4E0D;&#x8855;. &#x8003;&#x616E;&#x5230;&#x53EF;&#x79FB;&#x690D;&#x6027;, &#x5F15;&#x7528;&#x985E;&#x578B;&#x6216;&#x5305;&#x542B;&#x5F15;&#x7528;&#x985E;&#x578B;&#x7684;&#x5927;&#x5C0F;&#x5728;32&#x4F4D;&#x5E73;&#x98B1;&#x4E0A;&#x662F;4&#x500B;&#x5B57;&#x7BC0;, &#x5728;64&#x4F4D;&#x5E73;&#x98B1;&#x4E0A;&#x662F;8&#x500B;&#x5B57;&#x7BC0;.</p>
<p>&#x8A08;&#x7B97;&#x6A5F;&#x52A0;&#x8F09;&#x548C;&#x4FDD;&#x5B58;&#x6578;&#x64DA;&#x6642;, &#x5982;&#x679C;&#x5167;&#x5B58;&#x5730;&#x5740;&#x95A4;&#x7406;&#x5730;&#x5C0D;&#x9F4A;&#x7684;&#x5C07;&#x6703;&#x66F4;&#x6709;&#x6548;&#x7387;.
&#x4F8B;&#x5982; 2 &#x5B57;&#x7BC0;&#x5927;&#x5C0F;&#x7684; int16 &#x985E;&#x578B;&#x61C9;&#x8A72;&#x662F;&#x5076;&#x6578;, &#x4E00;&#x500B;4 &#x5B57;&#x7BC0;&#x5927;&#x5C0F;&#x7684; rune &#x985E;&#x578B;&#x5730;&#x5740;&#x61C9;&#x8A72;&#x662F; 4 &#x7684;&#x500D;&#x6578;, &#x4E00;&#x500B; 8 &#x5B57;&#x7BC0;&#x5927;&#x5C0F;&#x7684; float64, uint64 &#x6216; 64-bit &#x6307;&#x937C; &#x7684;&#x5730;&#x5740;&#x61C9;&#x8A72;&#x662F; 8 &#x5B57;&#x7BC0;&#x5C0D;&#x9F4A;&#x7684;. &#x4F46;&#x662F;&#x5C0D;&#x65BC;&#x518D;&#x5927;&#x7684;&#x5730;&#x5740;&#x5C0D;&#x9F4A;&#x500D;&#x6578;&#x5247;&#x662F;&#x4E0D;&#x9700;&#x8981;&#x7684;,
&#x537D;&#x4F7F;&#x662F; complex128 &#x7B49;&#x8F03;&#x5927;&#x7684;&#x6578;&#x64DA;&#x985E;&#x578B;.</p>
<p>&#x7531;&#x65BC;&#x9019;&#x500B;&#x56E0;&#x7D20;,&#x4E00;&#x500B;&#x805A;&#x95A4;&#x985E;&#x578B;(&#x7D50;&#x69CB;&#x9AD4;&#x6216;&#x6578;&#x7D44;)&#x7684;&#x5927;&#x5C0F;&#x81F3;&#x5C11;&#x662F;&#x6240;&#x6709;&#x5B57;&#x6BB5;&#x6216;&#x5143;&#x7D20;&#x5927;&#x5C0F;&#x7684;&#x7E3D;&#x548C;, &#x6216;&#x8005;&#x66F4;&#x5927;&#x56E0;&#x70BA;&#x53EF;&#x80FD;&#x5B58;&#x5728;&#x7A7A;&#x6D1E;. &#x7A7A;&#x6D1E;&#x662F;&#x7DE8;&#x8B6F;&#x5668;&#x81EA;&#x52D5;&#x6DFB;&#x52A0;&#x7684;&#x6C92;&#x6709;&#x88AB;&#x4F7F;&#x7528;&#x7684;&#x7A7A;&#x9593;, &#x7528;&#x65BC;&#x4FDD;&#x8B49;&#x5F8C;&#x9EAB;&#x6BCF;&#x500B;&#x5B57;&#x6BB5;&#x6216;&#x5143;&#x7D20;&#x7684;&#x5730;&#x5740;&#x76F8;&#x5C0D;&#x65BC;&#x7D50;&#x69CB;&#x6216;&#x6578;&#x7D44;&#x7684;&#x958B;&#x59CB;&#x5730;&#x5740;&#x80FD;&#x5920;&#x95A4;&#x7406;&#x5730;&#x5C0D;&#x9F4A;.</p>
<table>
<thead>
<tr>
<th>&#x985E;&#x578B;</th>
<th>&#x5927;&#x5C0F;</th>
</tr>
</thead>
<tbody>
<tr>
<td>bool</td>
<td>1&#x5B57;&#x7BC0;</td>
</tr>
<tr>
<td>intN, uintN, floatN, complexN</td>
<td>N/8&#x5B57;&#x7BC0; (&#x4F8B;&#x5982; float64 &#x662F; 8&#x5B57;&#x7BC0;)</td>
</tr>
<tr>
<td>int, uint, uintptr</td>
<td>1&#x500B;&#x6A5F;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td>*T</td>
<td>1&#x500B;&#x6A5F;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td>string</td>
<td>2&#x500B;&#x6A5F;&#x5668;&#x5B57;(data,len)</td>
</tr>
<tr>
<td>[]T</td>
<td>3&#x500B;&#x6A5F;&#x5668;&#x5B57;(data,len, cap)</td>
</tr>
<tr>
<td>map</td>
<td>1&#x500B;&#x6A5F;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td>func</td>
<td>1&#x500B;&#x6A5F;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td>chan</td>
<td>1&#x500B;&#x6A5F;&#x5668;&#x5B57;</td>
</tr>
<tr>
<td>interface</td>
<td>2&#x500B;&#x6A5F;&#x5668;&#x5B57;(type,value)</td>
</tr>
</tbody>
</table>
<p>Go&#x7684;&#x8A9E;&#x8A00;&#x898F;&#x7BC4;&#x4F75;&#x6C92;&#x6709;&#x4FDD;&#x8B49;&#x4E00;&#x500B;&#x5B57;&#x6BB5;&#x7684;&#x8072;&#x660E;&#x9806;&#x5E8F;&#x548C;&#x5167;&#x5B58;&#x4E2D;&#x7684;&#x9806;&#x5E8F;&#x662F;&#x4E00;&#x7DFB;&#x7684;, &#x6240;&#x4EE5;&#x7406;&#x8AD6;&#x4E0A;&#x4E00;&#x500B;&#x7DE8;&#x8B6F;&#x5668;&#x53EF;&#x4EE5;&#x96A8;&#x610F;&#x5730;&#x91CD;&#x65B0;&#x6392;&#x5217;&#x6BCF;&#x500B;&#x5B57;&#x6BB5;&#x7684;&#x5167;&#x5B58;&#x4F48;&#x4FB7;, &#x96A8;&#x7740;&#x5728;&#x5BEB;&#x4F5C;&#x672C;&#x66F8;&#x7684;&#x6642;&#x5019;&#x7DE8;&#x8B6F;&#x5668;&#x9084;&#x6C92;&#x6709;&#x9019;&#x9EBC;&#x505A;. &#x4E0B;&#x9EAB;&#x7684;&#x4E09;&#x500B;&#x7D50;&#x69CB;&#x9AD4;&#x6709;&#x7740;&#x76F8;&#x8855;&#x7684;&#x5B57;&#x6BB5;, &#x4F46;&#x662F;&#x7B2C;&#x4E00;&#x500B;&#x6BD4;&#x53E6;&#x5916;&#x7684;&#x5169;&#x500B;&#x9700;&#x8981;&#x591A; 50% &#x7684;&#x5167;&#x5B58;.</p>
<pre><code class="lang-Go"> <span class="hljs-comment">// 64-bit 32-bit</span>
<span class="hljs-keyword">struct</span>{ <span class="hljs-typename">bool</span>; <span class="hljs-typename">float64</span>; <span class="hljs-typename">int16</span> } <span class="hljs-comment">// 3 words 4words</span>
<span class="hljs-keyword">struct</span>{ <span class="hljs-typename">float64</span>; <span class="hljs-typename">int16</span>; <span class="hljs-typename">bool</span> } <span class="hljs-comment">// 2 words 3words</span>
<span class="hljs-keyword">struct</span>{ <span class="hljs-typename">bool</span>; <span class="hljs-typename">int16</span>; <span class="hljs-typename">float64</span> } <span class="hljs-comment">// 2 words 3words</span>
</code></pre>
<p>&#x96D6;&#x7136;&#x95DC;&#x65BC;&#x5C0D;&#x9F4A;&#x7B97;&#x6CD5;&#x7684;&#x7D30;&#x7BC0;&#x8D85;&#x9F63;&#x4E86;&#x672C;&#x66F8;&#x7684;&#x7BC4;&#x570D;, &#x4E5F;&#x4E0D;&#x662F;&#x6BCF;&#x4E00;&#x500B;&#x7D50;&#x69CB;&#x9AD4;&#x90FD;&#x9700;&#x8981;&#x64D4;&#x5FC3;&#x9019;&#x500B;&#x554F;&#x984C;, &#x4E0D;&#x904E;&#x6709;&#x6548;&#x7684;&#x5305;&#x88DD;&#x53EF;&#x4EE5;&#x4F7F;&#x6578;&#x64DA;&#x7D50;&#x69CB;&#x66F4;&#x52A0;&#x7DCA;&#x6E4A;, &#x5167;&#x5B58;&#x4F7F;&#x7528;&#x7387;&#x548C;&#x6027;&#x80FD;&#x90FD;&#x53EF;&#x80FD;&#x53D7;&#x76CA;.</p>
<p><code>unsafe.Alignof</code> &#x51FD;&#x6578;&#x8FD4;&#x8FF4;&#x5C0D;&#x61C9;&#x53C3;&#x6578;&#x7684;&#x985E;&#x578B;&#x9700;&#x8981;&#x5C0D;&#x9F4A;&#x7684;&#x500D;&#x6578;. &#x548C; Sizeof &#x985E;&#x4F3C;, Alignof &#x4E5F;&#x662F;&#x8FD4;&#x8FF4;&#x4E00;&#x500B;&#x5E38;&#x91CF;&#x9336;&#x9054;&#x5F0F;, &#x5C0D;&#x61C9;&#x4E00;&#x500B;&#x5E38;&#x91CF;. &#x901A;&#x5E38;&#x60C5;&#x6CC1;&#x4E0B;&#x4F48;&#x723E;&#x548C;&#x6578;&#x5B57;&#x985E;&#x578B;&#x9700;&#x8981;&#x5C0D;&#x9F4A;&#x5230;&#x5B83;&#x5011;&#x672C;&#x8EAB;&#x7684;&#x5927;&#x5C0F;(&#x6700;&#x591A;8&#x500B;&#x5B57;&#x7BC0;), &#x5176;&#x5B83;&#x7684;&#x985E;&#x578B;&#x5C0D;&#x9F4A;&#x5230;&#x6A5F;&#x5668;&#x5B57;&#x5927;&#x5C0F;.</p>
<p><code>unsafe.Offsetof</code> &#x51FD;&#x6578;&#x7684;&#x53C3;&#x6578;&#x5FC5;&#x9B1A;&#x662F;&#x4E00;&#x500B;&#x5B57;&#x6BB5; <code>x.f</code>, &#x7136;&#x5F8C;&#x8FD4;&#x8FF4; <code>f</code> &#x5B57;&#x6BB5;&#x76F8;&#x5C0D;&#x65BC; <code>x</code> &#x8D77;&#x59CB;&#x5730;&#x5740;&#x7684;&#x504F;&#x79FB;&#x91CF;, &#x5305;&#x62EC;&#x53EF;&#x80FD;&#x7684;&#x7A7A;&#x6D1E;.</p>
<p>&#x5716; 13.1 &#x986F;&#x793A;&#x4E86;&#x4E00;&#x500B;&#x7D50;&#x69CB;&#x9AD4;&#x8B8A;&#x91CF; x &#x4EE5;&#x53CA;&#x5176;&#x5728;32&#x4F4D;&#x548C;64&#x4F4D;&#x6A5F;&#x5668;&#x4E0A;&#x7684;&#x5178;&#x578B;&#x7684;&#x5167;&#x5B58;. &#x7070;&#x8272;&#x5340;&#x57DF;&#x662F;&#x7A7A;&#x6D1E;.</p>
<pre><code class="lang-Go"><span class="hljs-keyword">var</span> x <span class="hljs-keyword">struct</span> {
a <span class="hljs-typename">bool</span>
b <span class="hljs-typename">int16</span>
c []<span class="hljs-typename">int</span>
}
</code></pre>
<p>The table below shows the results of applying the three unsafe functions to x itself and to each of its three &#xFB01;elds:</p>
<p>&#x4E0B;&#x9EAB;&#x986F;&#x793A;&#x4E86;&#x61C9;&#x7528;&#x4E09;&#x500B;&#x51FD;&#x6578;&#x5C0D; x &#x548C;&#x5B83;&#x7684;&#x4E09;&#x500B;&#x5B57;&#x6BB5;&#x8A08;&#x7B97;&#x7684;&#x7D50;&#x679C;:</p>
<p><img src="../images/ch13-01.png" alt=""></p>
<p>32&#x4F4D;&#x7E6B;&#x7D71;:</p>
<pre><code>Sizeof(x) = 16 Alignof(x) = 4
Sizeof(x.a) = 1 Alignof(x.a) = 1 Offsetof(x.a) = 0
Sizeof(x.b) = 2 Alignof(x.b) = 2 Offsetof(x.b) = 2
Sizeof(x.c) = 12 Alignof(x.c) = 4 Offsetof(x.c) = 4
</code></pre><p>64&#x4F4D;&#x7E6B;&#x7D71;:</p>
<pre><code>Sizeof(x) = 32 Alignof(x) = 8
Sizeof(x.a) = 1 Alignof(x.a) = 1 Offsetof(x.a) = 0
Sizeof(x.b) = 2 Alignof(x.b) = 2 Offsetof(x.b) = 2
Sizeof(x.c) = 24 Alignof(x.c) = 8 Offsetof(x.c) = 8
</code></pre><p>&#x96D6;&#x7136;&#x5B83;&#x5011;&#x5728;&#x4E0D;&#x5B89;&#x5168;&#x7684; unsafe &#x5305;, &#x4F46;&#x662F;&#x9019;&#x5E7E;&#x500B;&#x51FD;&#x6578;&#x4F75;&#x4E0D;&#x662F;&#x771E;&#x7684;&#x4E0D;&#x5B89;&#x5168;,
&#x7279;&#x5F46;&#x5728;&#x9700;&#x8981;&#x512A;&#x5316;&#x5167;&#x5B58;&#x7A7A;&#x9593;&#x6642;&#x5B83;&#x5011;&#x5C0D;&#x65BC;&#x7406;&#x89E3;&#x539F;&#x751F;&#x7684;&#x5167;&#x5B58;&#x4F48;&#x4FB7;&#x5F88;&#x6709;&#x5E6B;&#x52A9;.</p>
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