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<div class="book" data-level="13.2" data-chapter-title="unsafe.Pointer" data-filepath="ch13/ch13-02.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
</a>
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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>
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<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
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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>
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<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
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</ul>
</li>
<li class="chapter " data-level="3" data-path="ch3/ch3.html">
<a href="../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>
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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>
</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">
<i class="fa fa-check"></i>
<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>
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 " 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 active" 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
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<h2 id="132-unsafepointer">13.2. unsafe.Pointer</h2>
<p>&#x5927;&#x591A;&#x6578;&#x6307;&#x937C;&#x985E;&#x578B;&#x5BEB;&#x6210; <em>T, &#x542B;&#x7FA9;&#x662F; &quot;&#x4E00;&#x500B;&#x6307;&#x66CF;T&#x985E;&#x578B;&#x8B8A;&#x91CF;&#x7684;&#x6307;&#x937C;&quot;. <code>unsafe.Pointer</code> &#x662F;&#x7279;&#x5F46;&#x5B9A;&#x7FA9;&#x7684;&#x4E00;&#x7A2E;&#x6307;&#x937C;&#x985E;&#x578B;, &#x5B83;&#x53EF;&#x4EE5;&#x5305;&#x542B;&#x4EFB;&#x610F;&#x985E;&#x578B;&#x8B8A;&#x91CF;&#x7684;&#x5730;&#x5740;. &#x7576;&#x7136;, &#x6211;&#x5011;&#x4E0D;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x4F7F;&#x7528; </em>p &#x7A6B;&#x53D6; <code>unsafe.Pointer</code> &#x6307;&#x937C;&#x6307;&#x66CF;&#x7684;&#x771E;&#x5BE6;&#x8B8A;&#x91CF;, &#x56E0;&#x70BA;&#x6211;&#x5011;&#x4F75;&#x4E0D;&#x77E5;&#x9053;&#x8B8A;&#x91CF;&#x7684;&#x985E;&#x578B;. &#x548C;&#x666E;&#x901A;&#x6307;&#x937C;&#x4E00;&#x6A23;, <code>unsafe.Pointer</code> &#x6307;&#x937C;&#x662F;&#x53EF;&#x4EE5;&#x6BD4;&#x8F03;&#x7684;, &#x652F;&#x6301;&#x548C; nil &#x6BD4;&#x8F03;&#x5224;&#x65B7;&#x662F;&#x5426;&#x70BA;&#x7A7A;&#x6307;&#x937C;.</p>
<p>&#x4E00;&#x500B;&#x666E;&#x901A;&#x7684; <em>T &#x985E;&#x578B;&#x6307;&#x937C;&#x53EF;&#x4EE5;&#x88AB;&#x8F49;&#x5316;&#x70BA; <code>unsafe.Pointer</code> &#x985E;&#x578B;&#x6307;&#x937C;, &#x4F75;&#x4E14;&#x4E00;&#x500B; <code>unsafe.Pointer</code> &#x985E;&#x578B;&#x6307;&#x937C;&#x4E5F;&#x53EF;&#x4EE5;&#x88AB;&#x8F49;&#x8FF4;&#x666E;&#x901A;&#x6307;&#x937C;, &#x4E5F;&#x53EF;&#x4EE5;&#x662F;&#x548C; </em>T &#x4E0D;&#x8855;&#x985E;&#x578B;&#x7684;&#x6307;&#x937C;. &#x901A;&#x904E;&#x5C07; <code>*float64</code> &#x985E;&#x578B;&#x6307;&#x937C; &#x8F49;&#x5316;&#x70BA; <code>*uint64</code> &#x985E;&#x578B;&#x6307;&#x937C;, &#x6211;&#x5011;&#x53EF;&#x4EE5;&#x6AA2;&#x67FB;&#x4E00;&#x500B;&#x6D6E;&#x9EDE;&#x6578;&#x8B8A;&#x91CF;&#x7684;&#x4F4D;&#x6A21;&#x5F0F;.</p>
<pre><code class="lang-Go"><span class="hljs-keyword">package</span> math
<span class="hljs-keyword">func</span> Float64bits(f <span class="hljs-typename">float64</span>) <span class="hljs-typename">uint64</span> { <span class="hljs-keyword">return</span> *(*<span class="hljs-typename">uint64</span>)(unsafe.Pointer(&amp;f)) }
fmt.Printf(<span class="hljs-string">&quot;%#016x\n&quot;</span>, Float64bits(<span class="hljs-number">1.0</span>)) <span class="hljs-comment">// &quot;0x3ff0000000000000&quot;</span>
</code></pre>
<p>&#x901A;&#x904E;&#x65B0;&#x6307;&#x937C;, &#x6211;&#x5011;&#x53EF;&#x4EE5;&#x66F4;&#x65B0;&#x6D6E;&#x9EDE;&#x6578;&#x7684;&#x4F4D;&#x6A21;&#x5F0F;. &#x901A;&#x904E;&#x4F4D;&#x6A21;&#x5F0F;&#x64CD;&#x4F5C;&#x6D6E;&#x9EDE;&#x6578;&#x662F;&#x53EF;&#x4EE5;&#x7684;, &#x4F46;&#x662F;&#x66F4;&#x91CD;&#x8981;&#x7684;&#x610F;&#x7FA9;&#x662F;&#x6307;&#x937C;&#x8F49;&#x63DB;&#x8B93;&#x6211;&#x5011;&#x53EF;&#x4EE5;&#x5728;&#x4E0D;&#x7834;&#x58DE;&#x985E;&#x578B;&#x7E6B;&#x7D71;&#x7684;&#x524D;&#x63D0;&#x4E0B;&#x66CF;&#x5167;&#x5B58;&#x5BEB;&#x5165;&#x4EFB;&#x610F;&#x7684;&#x503C;.</p>
<p>&#x4E00;&#x500B; <code>unsafe.Pointer</code> &#x6307;&#x937C;&#x4E5F;&#x53EF;&#x4EE5;&#x88AB;&#x8F49;&#x5316;&#x70BA; uintptr &#x985E;&#x4F3C;, &#x7136;&#x5F8C;&#x4FDD;&#x5B58;&#x5230;&#x6307;&#x937C;&#x578B;&#x6578;&#x503C;&#x8B8A;&#x91CF;&#x4E2D;, &#x7528;&#x4EE5;&#x505A;&#x5FC5;&#x8981;&#x7684;&#x6307;&#x937C;&#x904B;&#x7B97;.
(&#x7B2C;&#x4E09;&#x7AE0;&#x5167;&#x5BB9;, uintptr&#x662F;&#x4E00;&#x500B;&#x7121;&#x7B26;&#x865F;&#x7684;&#x6574;&#x578B;&#x6578;, &#x8DB3;&#x6709;&#x4FDD;&#x5B58;&#x4E00;&#x500B;&#x5730;&#x5740;.)
&#x9019;&#x7A2E;&#x8F49;&#x63DB;&#x4E5F;&#x662F;&#x53EF;&#x9006;&#x7684;, &#x4F46;&#x662F;, &#x5C07; uintptr &#x8F49;&#x70BA; <code>unsafe.Pointer</code> &#x6307;&#x937C;&#x53EF;&#x80FD;&#x7834;&#x58DE;&#x985E;&#x578B;&#x7E6B;&#x7D71;, &#x56E0;&#x70BA;&#x4F75;&#x4E0D;&#x662F;&#x6240;&#x6709;&#x7684;&#x6578;&#x5B57;&#x90FD;&#x662F;&#x6709;&#x6548;&#x7684;&#x5167;&#x5B58;&#x5730;&#x5740;.</p>
<p>&#x8A31;&#x591A;&#x5C07; <code>unsafe.Pointer</code> &#x6307;&#x937C; &#x8F49;&#x70BA;&#x539F;&#x751F;&#x6578;&#x5B57;, &#x7136;&#x5F8C;&#x518D;&#x8F49;&#x70BA; <code>unsafe.Pointer</code> &#x6307;&#x937C;&#x7684;&#x64CD;&#x4F5C;&#x662F;&#x4E0D;&#x5B89;&#x5168;&#x7684;. &#x4E0B;&#x9EAB;&#x7684;&#x4F8B;&#x5B50;&#x9700;&#x8981;&#x5C07;&#x8B8A;&#x91CF; x &#x7684;&#x5730;&#x5740;&#x52A0;&#x4E0A; b &#x5B57;&#x6BB5;&#x7684;&#x504F;&#x79FB;&#x8F49;&#x5316;&#x70BA; *int16 &#x985E;&#x578B;&#x6307;&#x937C;, &#x7136;&#x5F8C;&#x901A;&#x904E;&#x8A72;&#x6307;&#x937C;&#x66F4;&#x65B0; <code>x.b</code>:</p>
<pre><code class="lang-Go"><span class="hljs-comment">//gopl.io/ch13/unsafeptr</span>
<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>
}
<span class="hljs-comment">// &#x548C; pb := &amp;x.b &#x7B49;&#x50F9;</span>
pb := (*<span class="hljs-typename">int16</span>)(unsafe.Pointer(
<span class="hljs-typename">uintptr</span>(unsafe.Pointer(&amp;x)) + unsafe.Offsetof(x.b)))
*pb = <span class="hljs-number">42</span>
fmt.Println(x.b) <span class="hljs-comment">// &quot;42&quot;</span>
</code></pre>
<p>&#x76E1;&#x7BA1;&#x5BEB;&#x6CD5;&#x5F88;&#x7E41;&#x7463;, &#x4F46;&#x5728;&#x9019;&#x88CF;&#x4F75;&#x4E0D;&#x662F;&#x4E00;&#x4EF6;&#x58DE;&#x4E8B;, &#x56E0;&#x70BA;&#x9019;&#x4E9B;&#x529F;&#x80FD;&#x61C9;&#x8A72;&#x5F88;&#x8B39;&#x614E;&#x5730;&#x4F7F;&#x7528;. &#x4E0D;&#x8981;&#x8A66;&#x5716;&#x5C07;&#x5F15;&#x5165;&#x53EF;&#x80FD;&#x800C;&#x7834;&#x58DE;&#x4EE3;&#x78BC;&#x7684;&#x6B63;&#x78BA;&#x6027;&#x7684; uintptr &#x81E8;&#x6642;&#x8B8A;&#x91CF;. &#x4E0B;&#x9EAB;&#x6BB5;&#x4EE3;&#x78BC;&#x662F;&#x4E0D;&#x6B63;&#x78BA;&#x7684;:</p>
<p>&#x932F;&#x8AA4;&#x7684;&#x539F;&#x56E0;&#x5F88;&#x5FAE;&#x5999;. &#x6709;&#x6642;&#x5019;&#x5783;&#x573E;&#x8FF4;&#x6536;&#x5668;&#x6703;&#x79FB;&#x52D5;&#x4E00;&#x4E9B;&#x8B8A;&#x91CF;&#x4EE5;&#x964D;&#x4F4E;&#x5167;&#x5B58;&#x788E;&#x7247;&#x7684;&#x554F;&#x984C;.&#x9019;&#x985E;&#x5783;&#x573E;&#x8FF4;&#x6536;&#x5668;&#x88AB;&#x7A31;&#x70BA;&#x79FB;&#x52D5;GC. &#x7576;&#x4E00;&#x500B;&#x8B8A;&#x91CF;&#x88AB;&#x79FB;&#x52D5;, &#x6240;&#x6709;&#x7684;&#x4FDD;&#x5B58;&#x6539;&#x8B8A;&#x91CF;&#x820A;&#x5730;&#x5740;&#x7684;&#x6307;&#x937C;&#x5FC5;&#x9B1A;&#x8855;&#x6642;&#x88AB;&#x66F4;&#x65B0;&#x70BA;&#x8B8A;&#x91CF;&#x79FB;&#x52D5;&#x5F8C;&#x7684;&#x65B0;&#x5730;&#x5740;. &#x5F9E;&#x5783;&#x573E;&#x6536;&#x96C6;&#x5668;&#x7684;&#x8996;&#x89D2;&#x4F86;&#x770B;, &#x4E00;&#x500B; <code>unsafe.Pointer</code> &#x662F;&#x4E00;&#x500B;&#x6307;&#x937C;, &#x56E0;&#x6B64;&#x7576;&#x8B8A;&#x91CF;&#x88AB;&#x79FB;&#x52D5;&#x662F;&#x5C0D;&#x61C9;&#x7684;&#x6307;&#x937C;&#x5FC5;&#x9B1A;&#x88AB;&#x66F4;&#x65B0;, &#x4F46;&#x662F; <code>uintptr</code> &#x96BB;&#x662F;&#x4E00;&#x500B;&#x666E;&#x901A;&#x7684;&#x6578;&#x5B57;, &#x6240;&#x4EE5;&#x5176;&#x503C;&#x4E0D;&#x61C9;&#x8A72;&#x88AB;&#x6539;&#x8B8A;. &#x4E0A;&#x9EAB;&#x932F;&#x8AA4;&#x7684;&#x4EE3;&#x78BC;&#x56E0;&#x70BA;&#x4E00;&#x500B;&#x975E;&#x6307;&#x937C;&#x7684;&#x81E8;&#x6642;&#x8B8A;&#x91CF; <code>tmp</code>, &#x5C0E;&#x7DFB;&#x5783;&#x573E;&#x6536;&#x96C6;&#x5668;&#x7121;&#x6CD5;&#x6B63;&#x78BA;&#x8B58;&#x5F46;&#x9019;&#x500B;&#x662F;&#x4E00;&#x500B;&#x6307;&#x66CF;&#x8B8A;&#x91CF; <code>x</code> &#x7684;&#x6307;&#x937C;. &#x7B2C;&#x4E8C;&#x500B;&#x8A9E;&#x53E5;&#x57F7;&#x884C;&#x6642;, &#x8B8A;&#x91CF; <code>x</code> &#x53EF;&#x80FD;&#x5DF2;&#x7D93;&#x88AB;&#x8F49;&#x79FB;, &#x81E8;&#x6642;&#x8B8A;&#x91CF; <code>tmp</code> &#x4E5F;&#x5C31;&#x4E0D;&#x5728;&#x5C0D;&#x61C9;&#x73FE;&#x5728;&#x7684; <code>&amp;x.b</code>. &#x7B2C;&#x4E09;&#x500B;&#x8CE6;&#x503C;&#x8A9E;&#x53E5;&#x5C07;&#x5FB9;&#x5E95;&#x6467;&#x8B6D;&#x90A3;&#x500B;&#x4E4B;&#x524D;&#x7684;&#x90A3;&#x90E8;&#x5206;&#x5167;&#x5B58;&#x7A7A;&#x9593;.</p>
<p>&#x6709;&#x5F88;&#x591A;&#x985E;&#x4F3C;&#x539F;&#x56E0;&#x5C0E;&#x7DFB;&#x7684;&#x932F;&#x8AA4;. &#x4F8B;&#x5982;&#x9019;&#x689D;&#x8A9E;&#x53E5;:</p>
<pre><code class="lang-Go">pT := <span class="hljs-typename">uintptr</span>(unsafe.Pointer(<span class="hljs-built_in">new</span>(T))) <span class="hljs-comment">// &#x63D0;&#x793A;: &#x932F;&#x8AA4;!</span>
</code></pre>
<p>&#x9019;&#x88CF;&#x4F75;&#x6C92;&#x6709;&#x6307;&#x937C;&#x5F15;&#x7528; <code>new</code> &#x65B0;&#x5275;&#x5EFA;&#x7684;&#x8B8A;&#x91CF;, &#x56E0;&#x6B64;&#x8A9E;&#x53E5;&#x57F7;&#x884C;&#x5B8C;&#x6210;&#x4E4B;&#x5F8C;, &#x5783;&#x573E;&#x6536;&#x96C6;&#x5668;&#x6709;&#x6B0A;&#x8FF4;&#x6536;&#x5176;&#x5167;&#x5B58;&#x7A7A;&#x9593;, &#x6240;&#x4EE5;&#x8FD4;&#x8FF4;&#x7684; <code>pT</code> &#x4FDD;&#x5B58;&#x5C07;&#x662F;&#x7121;&#x6548;&#x7684;&#x5730;&#x5740;.</p>
<p>&#x76EE;&#x524D;&#x7684;Go&#x8A9E;&#x8A00;&#x5BE6;&#x73FE;&#x9084;&#x6C92;&#x6709;&#x4F7F;&#x7528;&#x79FB;&#x52D5;GC(&#x672A;&#x4F86;&#x53EF;&#x80FD;&#x5BE6;&#x73FE;), &#x4F46;&#x9019;&#x4E0D;&#x8A72;&#x662F;&#x50E5;&#x5016;&#x7684;&#x7406;&#x7531;: &#x7576;&#x524D;&#x7684;Go&#x5BE6;&#x73FE;&#x5DF2;&#x7D93;&#x6709;&#x79FB;&#x52D5;&#x8B8A;&#x91CF;&#x7684;&#x5834;&#x666F;. &#x5728;5.2&#x7BC0;&#x6211;&#x5011;&#x63D0;&#x5230;goroutine&#x7684;&#x68E7;&#x662F;&#x6839;&#x64DA;&#x9700;&#x8981;&#x52D5;&#x614B;&#x589E;&#x9577;&#x7684;. &#x7576;&#x9019;&#x500B;&#x6642;&#x5019;, &#x539F;&#x4F86;&#x68E7;&#x4E2D;&#x7684;&#x6240;&#x4EE5;&#x8B8A;&#x91CF;&#x53EF;&#x80FD;&#x9700;&#x8981;&#x88AB;&#x79FB;&#x52D5;&#x5230;&#x65B0;&#x7684;&#x66F4;&#x5927;&#x7684;&#x68E7;&#x4E2D;, &#x6240;&#x4EE5;&#x6211;&#x5011;&#x7121;&#x6CD5;&#x78BA;&#x4FDD;&#x8B8A;&#x91CF;&#x7684;&#x5730;&#x5740;&#x5728;&#x6574;&#x500B;&#x4F7F;&#x7528;&#x9031;&#x671F;&#x5167;&#x4FDD;&#x6301;&#x4E0D;&#x8B8A;.</p>
<p>&#x5728;&#x7DE8;&#x5BEB;&#x672C;&#x6587;&#x6642;, &#x9084;&#x6C92;&#x6709;&#x6E05;&#x6670;&#x7684;&#x539F;&#x5247;&#x5C31;&#x6307;&#x5F15;Go&#x7A0B;&#x5E8F;&#x54E1;, &#x4EC0;&#x9EBC;&#x6A23; <code>unsafe.Pointer</code> &#x548C; <code>uintptr</code> &#x7684;&#x8F49;&#x63DB;&#x662F;&#x4E0D;&#x5B89;&#x5168;&#x7684;(&#x53C3;&#x8003; <a href="https://github.com/golang/go/issues/7192" target="_blank">Go issue7192</a>. &#x8B6F;&#x8A3B;: &#x8A72;&#x554F;&#x984C;&#x5DF2;&#x7D93;&#x8129;&#x5FA9;.), &#x56E0;&#x6B64;&#x6211;&#x5011;&#x5F37;&#x70C8;&#x5EFA;&#x8B70;&#x6309;&#x7167;&#x6700;&#x58DE;&#x7684;&#x65B9;&#x5F0F;&#x8655;&#x7406;. &#x5C07;&#x6240;&#x6709;&#x5305;&#x542B;&#x8B8A;&#x91CF; <code>y</code> &#x5730;&#x5740;&#x7684; <code>uintptr</code> &#x985E;&#x578B;&#x8B8A;&#x91CF;&#x7576;&#x4F5C; BUG &#x8655;&#x7406;, &#x8855;&#x6642;&#x6E1B;&#x5C11;&#x4E0D;&#x5FC5;&#x8981;&#x7684; <code>unsafe.Pointer</code> &#x5230; <code>uintptr</code> &#x7684;&#x8F49;&#x63DB;. &#x5728;&#x7B2C;&#x4E00;&#x500B;&#x4F8B;&#x5B50;&#x4E2D;, &#x6709;&#x4E09;&#x500B;&#x5230; <code>uintptr</code> &#x7684;&#x8F49;&#x63DB;, &#x5B57;&#x6BB5;&#x504F;&#x79FB;&#x91CF;&#x7684;&#x904B;&#x7B97;, &#x6240;&#x6709;&#x7684;&#x8F49;&#x63DB;&#x5168;&#x5728;&#x4E00;&#x500B;&#x9336;&#x9054;&#x5F0F;&#x5B8C;&#x6210;.</p>
<p>&#x7576;&#x8ABF;&#x7528;&#x4E00;&#x500B;&#x5EAB;&#x51FD;&#x6578;, &#x4F75;&#x4E14;&#x8FD4;&#x8FF4;&#x7684;&#x662F; <code>uintptr</code> &#x985E;&#x578B;&#x662F;, &#x6BD4;&#x5982;&#x4E0B;&#x9EAB;&#x53CD;&#x5C04;&#x5305;&#x4E2D;&#x7684;&#x76F8;&#x95DC;&#x51FD;&#x6578;,
&#x8FD4;&#x8FF4;&#x7684;&#x7D50;&#x679C;&#x61C9;&#x8A72;&#x7ACB;&#x537D;&#x8F49;&#x63DB;&#x70BA; <code>unsafe.Pointer</code> &#x4EE5;&#x78BA;&#x4FDD;&#x6307;&#x937C;&#x6307;&#x66CF;&#x7684;&#x662F;&#x76F8;&#x8855;&#x7684;&#x8B8A;&#x91CF;.</p>
<pre><code class="lang-Go"><span class="hljs-keyword">package</span> reflect
<span class="hljs-keyword">func</span> (Value) Pointer() <span class="hljs-typename">uintptr</span>
<span class="hljs-keyword">func</span> (Value) UnsafeAddr() <span class="hljs-typename">uintptr</span>
<span class="hljs-keyword">func</span> (Value) InterfaceData() [<span class="hljs-number">2</span>]<span class="hljs-typename">uintptr</span> <span class="hljs-comment">// (index 1)</span>
</code></pre>
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