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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="Mon Dec 28 2015 16:03:52 GMT+0800 (中国标准时间)">
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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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<b>0.2.</b>
Go語言項目
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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>
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致謝
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</a>
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</ul>
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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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<b>1.1.</b>
Hello, World
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<li class="chapter " data-level="1.2" data-path="ch1/ch1-02.html">
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<b>1.2.</b>
命令行參數
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<b>1.3.</b>
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査找重複的行
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<a href="../ch1/ch1-04.html">
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<b>1.4.</b>
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GIF動畵
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</a>
</li>
<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>
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獲取URL
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</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>
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併發獲取多個URL
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</a>
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<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
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</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
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<b>2.</b>
程序結構
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<b>2.1.</b>
命名
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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
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<li class="chapter " data-level="2.3" data-path="ch2/ch2-03.html">
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<b>2.3.</b>
變量
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<b>2.4.</b>
賦值
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<b>2.5.</b>
類型
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<b>2.6.</b>
包和文件
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<a href="../ch2/ch2-07.html">
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<b>2.7.</b>
作用域
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</ul>
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<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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<b>3.1.</b>
整型
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<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>
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<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>
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複數
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</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>
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布爾型
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</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>
</li>
<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>
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</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>
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複合數據類型
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</a>
<ul class="articles">
<li class="chapter " data-level="4.1" data-path="ch4/ch4-01.html">
<a href="../ch4/ch4-01.html">
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<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">
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<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">
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<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">
<i class="fa fa-check"></i>
<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>
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Recover捕獲異常
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</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>
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基於指針對象的方法
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</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>
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方法值和方法表達式
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</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>
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接口是合約
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</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>
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示例: 表達式求值
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</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>
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基於類型斷言識别錯誤類型
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</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>
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示例: 併發的Clock服務
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</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>
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示例: 併發的Echo服務
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</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>
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示例: 併發的Web爬蟲
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</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>
2015-12-21 04:55:18 +00:00
基於select的多路複用
2015-12-09 07:57:17 +00:00
</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>
2015-12-21 04:55:18 +00:00
示例: 併發的字典遍歷
2015-12-09 07:57:17 +00:00
</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>
2015-12-28 08:08:26 +00:00
併發的退出
2015-12-09 07:57:17 +00:00
</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>
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基於共享變量的併發
2015-12-09 07:57:17 +00:00
</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>
2015-12-21 04:55:18 +00:00
內存同步
2015-12-09 07:57:17 +00:00
</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>
2015-12-21 04:55:18 +00:00
示例: 併發的非阻塞緩存
2015-12-09 07:57:17 +00:00
</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>
2015-12-21 04:55:18 +00:00
Goroutines和線程
2015-12-09 07:57:17 +00:00
</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>
2015-12-21 04:55:18 +00:00
爲何需要反射?
2015-12-09 07:57:17 +00:00
</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>
2015-12-21 04:55:18 +00:00
示例: 編碼S表達式
2015-12-09 07:57:17 +00:00
</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>
2015-12-21 04:55:18 +00:00
示例: 解碼S表達式
2015-12-09 07:57:17 +00:00
</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>
2015-12-28 08:08:26 +00:00
獲取結構體字段標識
2015-12-09 07:57:17 +00:00
</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>
2015-12-24 06:47:06 +00:00
<li class="chapter " data-level="14" data-path="CONTRIBUTORS.html">
2015-12-09 07:57:17 +00:00
2015-12-24 06:47:06 +00:00
<a href="../CONTRIBUTORS.html">
2015-12-09 07:57:17 +00:00
<i class="fa fa-check"></i>
2015-12-21 04:55:18 +00:00
<b>14.</b>
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2015-12-24 06:47:06 +00:00
附録
2015-12-09 07:57:17 +00:00
</a>
</li>
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<a href="https://www.gitbook.com" target="blank" class="gitbook-link">
本書使用 GitBook 釋出
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<h2 id="131-unsafesizeof-alignof-&#x548C;-offsetof">13.1. unsafe.Sizeof, Alignof &#x548C; Offsetof</h2>
2015-12-24 06:47:06 +00:00
<p>unsafe.Sizeof&#x51FD;&#x6578;&#x8FD4;&#x8FF4;&#x64CD;&#x4F5C;&#x6578;&#x5728;&#x5167;&#x5B58;&#x4E2D;&#x7684;&#x5B57;&#x7BC0;&#x5927;&#x5C0F;&#xFF0C;&#x53C3;&#x6578;&#x53EF;&#x4EE5;&#x662F;&#x4EFB;&#x610F;&#x985E;&#x578B;&#x7684;&#x8868;&#x9054;&#x5F0F;&#xFF0C;&#x4F46;&#x662F;&#x5B83;&#x4F75;&#x4E0D;&#x6703;&#x5C0D;&#x8868;&#x9054;&#x5F0F;&#x9032;&#x884C;&#x6C42;&#x503C;&#x3002;&#x4E00;&#x500B;Sizeof&#x51FD;&#x6578;&#x8ABF;&#x7528;&#x662F;&#x4E00;&#x500B;&#x5C0D;&#x61C9;uintptr&#x985E;&#x578B;&#x7684;&#x5E38;&#x91CF;&#x8868;&#x9054;&#x5F0F;&#xFF0C;&#x56E0;&#x6B64;&#x8FD4;&#x8FF4;&#x7684;&#x7D50;&#x679C;&#x53EF;&#x4EE5;&#x7528;&#x4F5C;&#x6578;&#x7D44;&#x985E;&#x578B;&#x7684;&#x9577;&#x5EA6;&#x5927;&#x5C0F;&#xFF0C;&#x6216;&#x8005;&#x7528;&#x4F5C;&#x8A08;&#x7B97;&#x5176;&#x4ED6;&#x7684;&#x5E38;&#x91CF;&#x3002;</p>
2015-12-09 07:57:17 +00:00
<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>
2015-12-28 08:08:26 +00:00
<p>Sizeof&#x51FD;&#x6578;&#x8FD4;&#x8FF4;&#x7684;&#x5927;&#x5C0F;&#x96BB;&#x5305;&#x62EC;&#x6578;&#x64DA;&#x7D50;&#x69CB;&#x4E2D;&#x56FA;&#x5B9A;&#x7684;&#x90E8;&#x5206;&#xFF0C;&#x4F8B;&#x5982;&#x5B57;&#x7B26;&#x4E32;&#x5C0D;&#x61C9;&#x7D50;&#x69CB;&#x9AD4;&#x4E2D;&#x7684;&#x6307;&#x91DD;&#x548C;&#x5B57;&#x7B26;&#x4E32;&#x9577;&#x5EA6;&#x90E8;&#x5206;&#xFF0C;&#x4F46;&#x662F;&#x4F75;&#x4E0D;&#x5305;&#x542B;&#x6307;&#x91DD;&#x6307;&#x5411;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x5167;&#x5BB9;&#x3002;Go&#x8A9E;&#x8A00;&#x4E2D;&#x975E;&#x805A;&#x5408;&#x985E;&#x578B;&#x901A;&#x5E38;&#x6709;&#x4E00;&#x500B;&#x56FA;&#x5B9A;&#x7684;&#x5927;&#x5C0F;&#xFF0C;&#x76E1;&#x7BA1;&#x5728;&#x4E0D;&#x540C;&#x5DE5;&#x5177;&#x93C8;&#x4E0B;&#x751F;&#x6210;&#x7684;&#x5BE6;&#x969B;&#x5927;&#x5C0F;&#x53EF;&#x80FD;&#x6703;&#x6709;&#x6240;&#x4E0D;&#x540C;&#x3002;&#x8003;&#x616E;&#x5230;&#x53EF;&#x79FB;&#x690D;&#x6027;&#xFF0C;&#x5F15;&#x7528;&#x985E;&#x578B;&#x6216;&#x5305;&#x542B;&#x5F15;&#x7528;&#x985E;&#x578B;&#x7684;&#x5927;&#x5C0F;&#x5728;32&#x4F4D;&#x5E73;&#x53F0;&#x4E0A;&#x662F;4&#x500B;&#x5B57;&#x7BC0;&#xFF0C;&#x5728;64&#x4F4D;&#x5E73;&#x53F0;&#x4E0A;&#x662F;8&#x500B;&#x5B57;&#x7BC0;&#x3002;</p>
2015-12-24 06:47:06 +00:00
<p>&#x8A08;&#x7B97;&#x6A5F;&#x5728;&#x52A0;&#x8F09;&#x548C;&#x4FDD;&#x5B58;&#x6578;&#x64DA;&#x6642;&#xFF0C;&#x5982;&#x679C;&#x5167;&#x5B58;&#x5730;&#x5740;&#x5408;&#x7406;&#x5730;&#x5C0D;&#x9F4A;&#x7684;&#x5C07;&#x6703;&#x66F4;&#x6709;&#x6548;&#x7387;&#x3002;&#x4F8B;&#x5982;2&#x5B57;&#x7BC0;&#x5927;&#x5C0F;&#x7684;int16&#x985E;&#x578B;&#x7684;&#x8B8A;&#x91CF;&#x5730;&#x5740;&#x61C9;&#x8A72;&#x662F;&#x5076;&#x6578;&#xFF0C;&#x4E00;&#x500B;4&#x5B57;&#x7BC0;&#x5927;&#x5C0F;&#x7684;rune&#x985E;&#x578B;&#x8B8A;&#x91CF;&#x7684;&#x5730;&#x5740;&#x61C9;&#x8A72;&#x662F;4&#x7684;&#x500D;&#x6578;&#xFF0C;&#x4E00;&#x500B;8&#x5B57;&#x7BC0;&#x5927;&#x5C0F;&#x7684;float64&#x3001;uint64&#x6216;64-bit&#x6307;&#x91DD;&#x985E;&#x578B;&#x8B8A;&#x91CF;&#x7684;&#x5730;&#x5740;&#x61C9;&#x8A72;&#x662F;8&#x5B57;&#x7BC0;&#x5C0D;&#x9F4A;&#x7684;&#x3002;&#x4F46;&#x662F;&#x5C0D;&#x65BC;&#x518D;&#x5927;&#x7684;&#x5730;&#x5740;&#x5C0D;&#x9F4A;&#x500D;&#x6578;&#x5247;&#x662F;&#x4E0D;&#x9700;&#x8981;&#x7684;&#xFF0C;&#x537D;&#x4F7F;&#x662F;complex128&#x7B49;&#x8F03;&#x5927;&#x7684;&#x6578;&#x64DA;&#x985E;&#x578B;&#x6700;&#x591A;&#x4E5F;&#x96BB;&#x662F;8&#x5B57;&#x7BC0;&#x5C0D;&#x9F4A;&#x3002;</p>
<p>&#x7531;&#x65BC;&#x5730;&#x5740;&#x5C0D;&#x9F4A;&#x9019;&#x500B;&#x56E0;&#x7D20;&#xFF0C;&#x4E00;&#x500B;&#x805A;&#x5408;&#x985E;&#x578B;&#xFF08;&#x7D50;&#x69CB;&#x9AD4;&#x6216;&#x6578;&#x7D44;&#xFF09;&#x7684;&#x5927;&#x5C0F;&#x81F3;&#x5C11;&#x662F;&#x6240;&#x6709;&#x5B57;&#x6BB5;&#x6216;&#x5143;&#x7D20;&#x5927;&#x5C0F;&#x7684;&#x7E3D;&#x548C;&#xFF0C;&#x6216;&#x8005;&#x66F4;&#x5927;&#x56E0;&#x7232;&#x53EF;&#x80FD;&#x5B58;&#x5728;&#x5167;&#x5B58;&#x7A7A;&#x6D1E;&#x3002;&#x5167;&#x5B58;&#x7A7A;&#x6D1E;&#x662F;&#x7DE8;&#x8B6F;&#x5668;&#x81EA;&#x52D5;&#x6DFB;&#x52A0;&#x7684;&#x6C92;&#x6709;&#x88AB;&#x4F7F;&#x7528;&#x7684;&#x5167;&#x5B58;&#x7A7A;&#x9593;&#xFF0C;&#x7528;&#x65BC;&#x4FDD;&#x8B49;&#x5F8C;&#x9762;&#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;&#x5408;&#x7406;&#x5730;&#x5C0D;&#x9F4A;&#xFF08;&#x8B6F;&#x8A3B;&#xFF1A;&#x5167;&#x5B58;&#x7A7A;&#x6D1E;&#x53EF;&#x80FD;&#x6703;&#x5B58;&#x5728;&#x4E00;&#x4E9B;&#x96A8;&#x6A5F;&#x6578;&#x64DA;&#xFF0C;&#x53EF;&#x80FD;&#x6703;&#x5C0D;&#x7528;unsafe&#x5305;&#x76F4;&#x63A5;&#x64CD;&#x4F5C;&#x5167;&#x5B58;&#x7684;&#x8655;&#x7406;&#x7523;&#x751F;&#x5F71;&#x97FF;&#xFF09;&#x3002;</p>
2015-12-09 07:57:17 +00:00
<table>
<thead>
<tr>
<th>&#x985E;&#x578B;</th>
<th>&#x5927;&#x5C0F;</th>
</tr>
</thead>
<tbody>
<tr>
<td>bool</td>
2015-12-24 06:47:06 +00:00
<td>1&#x500B;&#x5B57;&#x7BC0;</td>
2015-12-09 07:57:17 +00:00
</tr>
<tr>
<td>intN, uintN, floatN, complexN</td>
2015-12-24 06:47:06 +00:00
<td>N/8&#x500B;&#x5B57;&#x7BC0;(&#x4F8B;&#x5982;float64&#x662F;8&#x500B;&#x5B57;&#x7BC0;)</td>
2015-12-09 07:57:17 +00:00
</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>
2015-12-24 06:47:06 +00:00
<td>3&#x500B;&#x6A5F;&#x5668;&#x5B57;(data,len,cap)</td>
2015-12-09 07:57:17 +00:00
</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>
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<p>Go&#x8A9E;&#x8A00;&#x7684;&#x898F;&#x8303;&#x4F75;&#x6C92;&#x6709;&#x8981;&#x6C42;&#x4E00;&#x500B;&#x5B57;&#x6BB5;&#x7684;&#x8072;&#x660E;&#x9806;&#x5E8F;&#x548C;&#x5167;&#x5B58;&#x4E2D;&#x7684;&#x9806;&#x5E8F;&#x662F;&#x4E00;&#x81F4;&#x7684;&#xFF0C;&#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;&#x4F4D;&#x7F6E;&#xFF0C;&#x96A8;&#x7136;&#x5728;&#x5BEB;&#x4F5C;&#x672C;&#x66F8;&#x7684;&#x6642;&#x5019;&#x7DE8;&#x8B6F;&#x5668;&#x9084;&#x6C92;&#x6709;&#x9019;&#x9EBD;&#x505A;&#x3002;&#x4E0B;&#x9762;&#x7684;&#x4E09;&#x500B;&#x7D50;&#x69CB;&#x9AD4;&#x96D6;&#x7136;&#x6709;&#x7740;&#x76F8;&#x540C;&#x7684;&#x5B57;&#x6BB5;&#xFF0C;&#x4F46;&#x662F;&#x7B2C;&#x4E00;&#x7A2E;&#x5BEB;&#x6CD5;&#x6BD4;&#x53E6;&#x5916;&#x7684;&#x5169;&#x500B;&#x9700;&#x8981;&#x591A;50%&#x7684;&#x5167;&#x5B58;&#x3002;</p>
<pre><code class="lang-Go"> <span class="hljs-comment">// 64-bit 32-bit</span>
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<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>
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<p>&#x95DC;&#x65BC;&#x5167;&#x5B58;&#x5730;&#x5740;&#x5C0D;&#x9F4A;&#x7B97;&#x6CD5;&#x7684;&#x7D30;&#x7BC0;&#x8D85;&#x51FA;&#x4E86;&#x672C;&#x66F8;&#x7684;&#x8303;&#x570D;&#xFF0C;&#x4E5F;&#x4E0D;&#x662F;&#x6BCF;&#x4E00;&#x500B;&#x7D50;&#x69CB;&#x9AD4;&#x90FD;&#x9700;&#x8981;&#x64D4;&#x5FC3;&#x9019;&#x500B;&#x554F;&#x984C;&#xFF0C;&#x4E0D;&#x904E;&#x6709;&#x6548;&#x7684;&#x5305;&#x88DD;&#x53EF;&#x4EE5;&#x4F7F;&#x6578;&#x64DA;&#x7D50;&#x69CB;&#x66F4;&#x52A0;&#x7DCA;&#x6E4A;&#xFF08;&#x8B6F;&#x8A3B;&#xFF1A;&#x672A;&#x4F86;&#x7684;Go&#x8A9E;&#x8A00;&#x7DE8;&#x8B6F;&#x5668;&#x61C9;&#x8A72;&#x6703;&#x9ED8;&#x8A8D;&#x512A;&#x5316;&#x7D50;&#x69CB;&#x9AD4;&#x7684;&#x9806;&#x5E8F;&#xFF0C;&#x7576;&#x7136;&#x7528;&#x65BC;&#x61C9;&#x8A72;&#x4E5F;&#x80FD;&#x5920;&#x6307;&#x5B9A;&#x5177;&#x9AD4;&#x7684;&#x5167;&#x5B58;&#x5E03;&#x5C40;&#xFF0C;&#x76F8;&#x540C;&#x8A0E;&#x8AD6;&#x8ACB;&#x53C3;&#x8003; <a href="https://github.com/golang/go/issues/10014" target="_blank">Issue10014</a> &#xFF09;&#xFF0C;&#x5167;&#x5B58;&#x4F7F;&#x7528;&#x7387;&#x548C;&#x6027;&#x80FD;&#x90FD;&#x53EF;&#x80FD;&#x6703;&#x53D7;&#x76CA;&#x3002;</p>
2015-12-21 04:55:18 +00:00
<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;&#x8868;&#x9054;&#x5F0F;, &#x5C0D;&#x61C9;&#x4E00;&#x500B;&#x5E38;&#x91CF;. &#x901A;&#x5E38;&#x60C5;&#x6CC1;&#x4E0B;&#x5E03;&#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>
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<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>
2015-12-24 06:47:06 +00:00
<p>&#x4E0B;&#x9762;&#x986F;&#x793A;&#x4E86;&#x5C0D;x&#x548C;&#x5B83;&#x7684;&#x4E09;&#x500B;&#x5B57;&#x6BB5;&#x8ABF;&#x7528;unsafe&#x5305;&#x76F8;&#x95DC;&#x51FD;&#x6578;&#x7684;&#x8A08;&#x7B97;&#x7D50;&#x679C;&#xFF1A;</p>
2015-12-09 07:57:17 +00:00
<p><img src="../images/ch13-01.png" alt=""></p>
2015-12-24 06:47:06 +00:00
<p>32&#x4F4D;&#x7E6B;&#x7D71;&#xFF1A;</p>
2015-12-09 07:57:17 +00:00
<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
2015-12-24 06:47:06 +00:00
</code></pre><p>64&#x4F4D;&#x7E6B;&#x7D71;&#xFF1A;</p>
2015-12-09 07:57:17 +00:00
<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
2015-12-24 06:47:06 +00:00
</code></pre><p>&#x96D6;&#x7136;&#x9019;&#x5E7E;&#x500B;&#x51FD;&#x6578;&#x5728;&#x4E0D;&#x5B89;&#x5168;&#x7684;unsafe&#x5305;&#xFF0C;&#x4F46;&#x662F;&#x9019;&#x5E7E;&#x500B;&#x51FD;&#x6578;&#x8ABF;&#x7528;&#x4F75;&#x4E0D;&#x662F;&#x771E;&#x7684;&#x4E0D;&#x5B89;&#x5168;&#xFF0C;&#x7279;&#x522B;&#x5728;&#x9700;&#x8981;&#x512A;&#x5316;&#x5167;&#x5B58;&#x7A7A;&#x9593;&#x6642;&#x5B83;&#x5011;&#x8FD4;&#x8FF4;&#x7684;&#x7D50;&#x679C;&#x5C0D;&#x65BC;&#x7406;&#x89E3;&#x539F;&#x751F;&#x7684;&#x5167;&#x5B58;&#x5E03;&#x5C40;&#x5F88;&#x6709;&#x5E6B;&#x52A9;&#x3002;</p>
2015-12-09 07:57:17 +00:00
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