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2240 lines
85 KiB
HTML
2240 lines
85 KiB
HTML
<!DOCTYPE HTML>
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<html lang="zh-tw" >
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<head>
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<meta charset="UTF-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge" />
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<title>通過cgo調用C代碼 | Go语言圣经</title>
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<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
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<meta name="HandheldFriendly" content="true"/>
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<link rel="next" href="../ch13/ch13-05.html" />
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<link rel="prev" href="../ch13/ch13-03.html" />
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</head>
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<body>
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<div class="book" data-level="13.4" data-chapter-title="通過cgo調用C代碼" data-filepath="ch13/ch13-04.md" data-basepath=".." data-revision="Thu Dec 31 2015 16:18:40 GMT+0800 (中国标准时间)">
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<div class="book-summary">
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<nav role="navigation">
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<ul class="summary">
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<li class="chapter " data-level="0" data-path="index.html">
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<a href="../index.html">
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<i class="fa fa-check"></i>
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前言
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</a>
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<ul class="articles">
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<li class="chapter " data-level="0.1" data-path="ch0/ch0-01.html">
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<a href="../ch0/ch0-01.html">
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<i class="fa fa-check"></i>
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<b>0.1.</b>
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Go語言起源
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</a>
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</li>
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<li class="chapter " data-level="0.2" data-path="ch0/ch0-02.html">
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<a href="../ch0/ch0-02.html">
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<i class="fa fa-check"></i>
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<b>0.2.</b>
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Go語言項目
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</a>
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</li>
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<li class="chapter " data-level="0.3" data-path="ch0/ch0-03.html">
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<a href="../ch0/ch0-03.html">
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<i class="fa fa-check"></i>
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<b>0.3.</b>
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本書的組織
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</a>
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</li>
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<li class="chapter " data-level="0.4" data-path="ch0/ch0-04.html">
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<a href="../ch0/ch0-04.html">
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<i class="fa fa-check"></i>
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<b>0.4.</b>
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更多的信息
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</a>
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</li>
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<li class="chapter " data-level="0.5" data-path="ch0/ch0-05.html">
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<a href="../ch0/ch0-05.html">
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<i class="fa fa-check"></i>
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<b>0.5.</b>
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致謝
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="1" data-path="ch1/ch1.html">
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<a href="../ch1/ch1.html">
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<i class="fa fa-check"></i>
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<b>1.</b>
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入門
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</a>
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<ul class="articles">
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<li class="chapter " data-level="1.1" data-path="ch1/ch1-01.html">
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<a href="../ch1/ch1-01.html">
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<i class="fa fa-check"></i>
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<b>1.1.</b>
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Hello, World
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</a>
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</li>
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<li class="chapter " data-level="1.2" data-path="ch1/ch1-02.html">
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<a href="../ch1/ch1-02.html">
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<i class="fa fa-check"></i>
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<b>1.2.</b>
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命令行參數
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</a>
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</li>
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<li class="chapter " data-level="1.3" data-path="ch1/ch1-03.html">
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<a href="../ch1/ch1-03.html">
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<i class="fa fa-check"></i>
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<b>1.3.</b>
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査找重複的行
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</a>
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</li>
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<li class="chapter " data-level="1.4" data-path="ch1/ch1-04.html">
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<a href="../ch1/ch1-04.html">
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<i class="fa fa-check"></i>
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<b>1.4.</b>
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GIF動畵
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</a>
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</li>
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<li class="chapter " data-level="1.5" data-path="ch1/ch1-05.html">
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<a href="../ch1/ch1-05.html">
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<i class="fa fa-check"></i>
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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>
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<li class="chapter " data-level="1.6" data-path="ch1/ch1-06.html">
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<a href="../ch1/ch1-06.html">
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<i class="fa fa-check"></i>
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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>
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<li class="chapter " data-level="1.7" data-path="ch1/ch1-07.html">
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<a href="../ch1/ch1-07.html">
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<i class="fa fa-check"></i>
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<b>1.7.</b>
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Web服務
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</a>
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</li>
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<li class="chapter " data-level="1.8" data-path="ch1/ch1-08.html">
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<a href="../ch1/ch1-08.html">
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<i class="fa fa-check"></i>
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<b>1.8.</b>
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本章要點
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="2" data-path="ch2/ch2.html">
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<a href="../ch2/ch2.html">
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<i class="fa fa-check"></i>
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<b>2.</b>
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程序結構
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</a>
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<ul class="articles">
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<li class="chapter " data-level="2.1" data-path="ch2/ch2-01.html">
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<a href="../ch2/ch2-01.html">
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<i class="fa fa-check"></i>
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<b>2.1.</b>
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命名
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</a>
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</li>
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<li class="chapter " data-level="2.2" data-path="ch2/ch2-02.html">
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<a href="../ch2/ch2-02.html">
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<i class="fa fa-check"></i>
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<b>2.2.</b>
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聲明
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</a>
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</li>
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<li class="chapter " data-level="2.3" data-path="ch2/ch2-03.html">
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<a href="../ch2/ch2-03.html">
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<i class="fa fa-check"></i>
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<b>2.3.</b>
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變量
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</a>
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</li>
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<li class="chapter " data-level="2.4" data-path="ch2/ch2-04.html">
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<a href="../ch2/ch2-04.html">
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<i class="fa fa-check"></i>
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<b>2.4.</b>
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賦值
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</a>
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</li>
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<li class="chapter " data-level="2.5" data-path="ch2/ch2-05.html">
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<a href="../ch2/ch2-05.html">
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<i class="fa fa-check"></i>
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<b>2.5.</b>
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類型
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</a>
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</li>
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<li class="chapter " data-level="2.6" data-path="ch2/ch2-06.html">
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<a href="../ch2/ch2-06.html">
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<i class="fa fa-check"></i>
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<b>2.6.</b>
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包和文件
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</a>
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</li>
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<li class="chapter " data-level="2.7" data-path="ch2/ch2-07.html">
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<a href="../ch2/ch2-07.html">
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<i class="fa fa-check"></i>
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<b>2.7.</b>
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作用域
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="3" data-path="ch3/ch3.html">
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<a href="../ch3/ch3.html">
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<i class="fa fa-check"></i>
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<b>3.</b>
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基礎數據類型
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</a>
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<ul class="articles">
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<li class="chapter " data-level="3.1" data-path="ch3/ch3-01.html">
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<a href="../ch3/ch3-01.html">
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<i class="fa fa-check"></i>
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<b>3.1.</b>
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整型
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</a>
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</li>
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<li class="chapter " data-level="3.2" data-path="ch3/ch3-02.html">
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<a href="../ch3/ch3-02.html">
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<i class="fa fa-check"></i>
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<b>3.2.</b>
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浮點數
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</a>
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</li>
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<li class="chapter " data-level="3.3" data-path="ch3/ch3-03.html">
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<a href="../ch3/ch3-03.html">
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<i class="fa fa-check"></i>
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<b>3.3.</b>
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複數
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</a>
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</li>
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<li class="chapter " data-level="3.4" data-path="ch3/ch3-04.html">
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<a href="../ch3/ch3-04.html">
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<i class="fa fa-check"></i>
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<b>3.4.</b>
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布爾型
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</a>
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</li>
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<li class="chapter " data-level="3.5" data-path="ch3/ch3-05.html">
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<a href="../ch3/ch3-05.html">
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<i class="fa fa-check"></i>
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<b>3.5.</b>
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字符串
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</a>
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</li>
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<li class="chapter " data-level="3.6" data-path="ch3/ch3-06.html">
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<a href="../ch3/ch3-06.html">
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<i class="fa fa-check"></i>
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<b>3.6.</b>
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常量
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="4" data-path="ch4/ch4.html">
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<a href="../ch4/ch4.html">
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<i class="fa fa-check"></i>
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<b>4.</b>
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複合數據類型
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</a>
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<ul class="articles">
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<li class="chapter " data-level="4.1" data-path="ch4/ch4-01.html">
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<a href="../ch4/ch4-01.html">
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<i class="fa fa-check"></i>
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<b>4.1.</b>
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數組
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</a>
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</li>
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<li class="chapter " data-level="4.2" data-path="ch4/ch4-02.html">
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<a href="../ch4/ch4-02.html">
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<i class="fa fa-check"></i>
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<b>4.2.</b>
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Slice
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</a>
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</li>
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<li class="chapter " data-level="4.3" data-path="ch4/ch4-03.html">
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<a href="../ch4/ch4-03.html">
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<i class="fa fa-check"></i>
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<b>4.3.</b>
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Map
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</a>
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</li>
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<li class="chapter " data-level="4.4" data-path="ch4/ch4-04.html">
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<a href="../ch4/ch4-04.html">
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<i class="fa fa-check"></i>
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<b>4.4.</b>
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結構體
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</a>
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</li>
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<li class="chapter " data-level="4.5" data-path="ch4/ch4-05.html">
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<a href="../ch4/ch4-05.html">
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<i class="fa fa-check"></i>
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<b>4.5.</b>
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JSON
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</a>
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</li>
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<li class="chapter " data-level="4.6" data-path="ch4/ch4-06.html">
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<a href="../ch4/ch4-06.html">
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<i class="fa fa-check"></i>
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<b>4.6.</b>
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文本和HTML模闆
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="5" data-path="ch5/ch5.html">
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<a href="../ch5/ch5.html">
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<i class="fa fa-check"></i>
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<b>5.</b>
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函數
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</a>
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<ul class="articles">
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<li class="chapter " data-level="5.1" data-path="ch5/ch5-01.html">
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<a href="../ch5/ch5-01.html">
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<i class="fa fa-check"></i>
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<b>5.1.</b>
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函數聲明
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</a>
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</li>
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<li class="chapter " data-level="5.2" data-path="ch5/ch5-02.html">
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<a href="../ch5/ch5-02.html">
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<i class="fa fa-check"></i>
|
|
|
|
<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">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<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捕獲異常
|
|
</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>
|
|
|
|
基於指針對象的方法
|
|
</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>
|
|
|
|
方法值和方法表達式
|
|
</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>
|
|
|
|
接口是合約
|
|
</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: 表達式求值
|
|
</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>
|
|
|
|
基於類型斷言識别錯誤類型
|
|
</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: 併發的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: 併發的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: 併發的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的多路複用
|
|
</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: 併發的字典遍歷
|
|
</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>
|
|
|
|
併發的退出
|
|
</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>
|
|
|
|
基於共享變量的併發
|
|
</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>
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<li class="chapter " data-level="9.2" data-path="ch9/ch9-02.html">
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<a href="../ch9/ch9-02.html">
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<i class="fa fa-check"></i>
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<b>9.2.</b>
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sync.Mutex互斥鎖
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</a>
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</li>
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<li class="chapter " data-level="9.3" data-path="ch9/ch9-03.html">
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<a href="../ch9/ch9-03.html">
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<i class="fa fa-check"></i>
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<b>9.3.</b>
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sync.RWMutex讀寫鎖
|
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</a>
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</li>
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<li class="chapter " data-level="9.4" data-path="ch9/ch9-04.html">
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<a href="../ch9/ch9-04.html">
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<i class="fa fa-check"></i>
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<b>9.4.</b>
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內存同步
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</a>
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</li>
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<li class="chapter " data-level="9.5" data-path="ch9/ch9-05.html">
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<a href="../ch9/ch9-05.html">
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<i class="fa fa-check"></i>
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<b>9.5.</b>
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sync.Once初始化
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</a>
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</li>
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<li class="chapter " data-level="9.6" data-path="ch9/ch9-06.html">
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<a href="../ch9/ch9-06.html">
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<i class="fa fa-check"></i>
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<b>9.6.</b>
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競爭條件檢測
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</a>
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</li>
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<li class="chapter " data-level="9.7" data-path="ch9/ch9-07.html">
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<a href="../ch9/ch9-07.html">
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<i class="fa fa-check"></i>
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<b>9.7.</b>
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示例: 併發的非阻塞緩存
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</a>
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</li>
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<li class="chapter " data-level="9.8" data-path="ch9/ch9-08.html">
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<a href="../ch9/ch9-08.html">
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<i class="fa fa-check"></i>
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<b>9.8.</b>
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Goroutines和線程
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</a>
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</li>
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</ul>
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</li>
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<li class="chapter " data-level="10" data-path="ch10/ch10.html">
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<a href="../ch10/ch10.html">
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<i class="fa fa-check"></i>
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<b>10.</b>
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包和工具
|
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</a>
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<ul class="articles">
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<li class="chapter " data-level="10.1" data-path="ch10/ch10-01.html">
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<a href="../ch10/ch10-01.html">
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<i class="fa fa-check"></i>
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<b>10.1.</b>
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簡介
|
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</a>
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</li>
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<li class="chapter " data-level="10.2" data-path="ch10/ch10-02.html">
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<a href="../ch10/ch10-02.html">
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<i class="fa fa-check"></i>
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<b>10.2.</b>
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導入路徑
|
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</a>
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</li>
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<li class="chapter " data-level="10.3" data-path="ch10/ch10-03.html">
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<a href="../ch10/ch10-03.html">
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<i class="fa fa-check"></i>
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<b>10.3.</b>
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包聲明
|
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</a>
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</li>
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<li class="chapter " data-level="10.4" data-path="ch10/ch10-04.html">
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<a href="../ch10/ch10-04.html">
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<i class="fa fa-check"></i>
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<b>10.4.</b>
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|
導入聲明
|
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</a>
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</li>
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<li class="chapter " data-level="10.5" data-path="ch10/ch10-05.html">
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<a href="../ch10/ch10-05.html">
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<i class="fa fa-check"></i>
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<b>10.5.</b>
|
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|
|
匿名導入
|
|
</a>
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</li>
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<li class="chapter " data-level="10.6" data-path="ch10/ch10-06.html">
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<a href="../ch10/ch10-06.html">
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<i class="fa fa-check"></i>
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<b>10.6.</b>
|
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|
|
包和命名
|
|
</a>
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</li>
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|
|
<li class="chapter " data-level="10.7" data-path="ch10/ch10-07.html">
|
|
|
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|
<a href="../ch10/ch10-07.html">
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<i class="fa fa-check"></i>
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<b>10.7.</b>
|
|
|
|
工具
|
|
</a>
|
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</li>
|
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</ul>
|
|
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</li>
|
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|
|
<li class="chapter " data-level="11" data-path="ch11/ch11.html">
|
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<a href="../ch11/ch11.html">
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|
|
<i class="fa fa-check"></i>
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<b>11.</b>
|
|
|
|
測試
|
|
</a>
|
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|
|
<ul class="articles">
|
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|
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|
|
<li class="chapter " data-level="11.1" data-path="ch11/ch11-01.html">
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<a href="../ch11/ch11-01.html">
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|
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<i class="fa fa-check"></i>
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<b>11.1.</b>
|
|
|
|
go test
|
|
</a>
|
|
|
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|
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</li>
|
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|
|
<li class="chapter " data-level="11.2" data-path="ch11/ch11-02.html">
|
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|
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|
<a href="../ch11/ch11-02.html">
|
|
|
|
<i class="fa fa-check"></i>
|
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|
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<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">
|
|
|
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|
|
<a href="../ch11/ch11-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
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<b>11.4.</b>
|
|
|
|
基準測試
|
|
</a>
|
|
|
|
|
|
</li>
|
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|
|
<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>
|
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|
|
<b>11.5.</b>
|
|
|
|
剖析
|
|
</a>
|
|
|
|
|
|
</li>
|
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|
|
<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">
|
|
|
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|
|
<a href="../ch12/ch12.html">
|
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|
|
<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>
|
|
|
|
爲何需要反射?
|
|
</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表達式
|
|
</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表達式
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="12.7" data-path="ch12/ch12-07.html">
|
|
|
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<a href="../ch12/ch12-07.html">
|
|
|
|
<i class="fa fa-check"></i>
|
|
|
|
<b>12.7.</b>
|
|
|
|
獲取結構體字段標識
|
|
</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">
|
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|
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<a href="../ch13/ch13.html">
|
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|
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<i class="fa fa-check"></i>
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|
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<b>13.</b>
|
|
|
|
底層編程
|
|
</a>
|
|
|
|
|
|
<ul class="articles">
|
|
|
|
|
|
<li class="chapter " data-level="13.1" data-path="ch13/ch13-01.html">
|
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|
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<a href="../ch13/ch13-01.html">
|
|
|
|
<i class="fa fa-check"></i>
|
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|
|
<b>13.1.</b>
|
|
|
|
unsafe.Sizeof, Alignof 和 Offsetof
|
|
</a>
|
|
|
|
|
|
</li>
|
|
|
|
<li class="chapter " data-level="13.2" data-path="ch13/ch13-02.html">
|
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|
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<a href="../ch13/ch13-02.html">
|
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|
|
<i class="fa fa-check"></i>
|
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|
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<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 active" data-level="13.4" data-path="ch13/ch13-04.html">
|
|
|
|
|
|
<a href="../ch13/ch13-04.html">
|
|
|
|
<i class="fa fa-check"></i>
|
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|
|
<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="CONTRIBUTORS.html">
|
|
|
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|
|
<a href="../CONTRIBUTORS.html">
|
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|
|
<i class="fa fa-check"></i>
|
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<b>14.</b>
|
|
|
|
附録
|
|
</a>
|
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|
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</li>
|
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|
|
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<li class="divider"></li>
|
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<li>
|
|
<a href="https://www.gitbook.com" target="blank" class="gitbook-link">
|
|
本書使用 GitBook 釋出
|
|
</a>
|
|
</li>
|
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</ul>
|
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</nav>
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</div>
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<div class="book-body">
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<div class="body-inner">
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<div class="book-header" role="navigation">
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<!-- Actions Left -->
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<!-- Title -->
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<h1>
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<i class="fa fa-circle-o-notch fa-spin"></i>
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<a href="../" >Go语言圣经</a>
|
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</h1>
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</div>
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<div class="page-wrapper" tabindex="-1" role="main">
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<div class="page-inner">
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<section class="normal" id="section-">
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<h2 id="134-通過cgo調用c代碼">13.4. 通過cgo調用C代碼</h2>
|
|
<p>Go程序可能會遇到要訪問C語言的某些硬件驅動函數的場景，或者是從一個C++語言實現的嵌入式數據庫査詢記録的場景，或者是使用Fortran語言實現的一些線性代數庫的場景。C語言作爲一個通用語言，很多庫會選擇提供一個C兼容的API，然後用其他不同的編程語言實現（譯者：Go語言需要也應該擁抱這些鉅大的代碼遺産）。</p>
|
|
<p>在本節中，我們將構建一個簡易的數據壓縮程序，使用了一個Go語言自帶的叫cgo的用於支援C語言函數調用的工具。這類工具一般被稱爲 <em>foreign-function interfaces</em> （簡稱ffi）, 併且在類似工具中cgo也不是唯一的。SWIG（ <a href="http://swig.org" target="_blank">http://swig.org</a> ）是另一個類似的且被廣泛使用的工具，SWIG提供了很多複雜特性以支援C++的特性，但SWIG併不是我們要討論的主題。</p>
|
|
<p>在標準庫的<code>compress/...</code>子包有很多流行的壓縮算法的編碼和解碼實現，包括流行的LZW壓縮算法（Unix的compress命令用的算法）和DEFLATE壓縮算法（GNU gzip命令用的算法）。這些包的API的細節雖然有些差異，但是它們都提供了針對 io.Writer類型輸出的壓縮接口和提供了針對io.Reader類型輸入的解壓縮接口。例如：</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">package</span> gzip <span class="hljs-comment">// compress/gzip</span>
|
|
<span class="hljs-keyword">func</span> NewWriter(w io.Writer) io.WriteCloser
|
|
<span class="hljs-keyword">func</span> NewReader(r io.Reader) (io.ReadCloser, error)
|
|
</code></pre>
|
|
<p>bzip2壓縮算法，是基於優雅的Burrows-Wheeler變換算法，運行速度比gzip要慢，但是可以提供更高的壓縮比。標準庫的compress/bzip2包目前還沒有提供bzip2壓縮算法的實現。完全從頭開始實現是一個壓縮算法是一件繁瑣的工作，而且 <a href="http://bzip.org" target="_blank">http://bzip.org</a> 已經有現成的libbzip2的開源實現，不僅文檔齊全而且性能又好。</p>
|
|
<p>如果是比較小的C語言庫，我們完全可以用純Go語言重新實現一遍。如果我們對性能也沒有特殊要求的話，我們還可以用os/exec包的方法將C編寫的應用程序作爲一個子進程運行。隻有當你需要使用複雜而且性能更高的底層C接口時，就是使用cgo的場景了（譯註：用os/exec包調用子進程的方法會導致程序運行時依賴那個應用程序）。下面我們將通過一個例子講述cgo的具體用法。</p>
|
|
<p>譯註：本章采用的代碼都是最新的。因爲之前已經出版的書中包含的代碼隻能在Go1.5之前使用。從Go1.6開始，Go語言已經明確規定了哪些Go語言指針可以之間傳入C語言函數。新代碼重點是增加了bz2alloc和bz2free的兩個函數，用於bz_stream對象空間的申請和釋放操作。下面是新代碼中增加的註釋，説明這個問題：</p>
|
|
<pre><code class="lang-Go"><span class="hljs-comment">// The version of this program that appeared in the first and second</span>
|
|
<span class="hljs-comment">// printings did not comply with the proposed rules for passing</span>
|
|
<span class="hljs-comment">// pointers between Go and C, described here:</span>
|
|
<span class="hljs-comment">// https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md</span>
|
|
<span class="hljs-comment">//</span>
|
|
<span class="hljs-comment">// The rules forbid a C function like bz2compress from storing 'in'</span>
|
|
<span class="hljs-comment">// and 'out' (pointers to variables allocated by Go) into the Go</span>
|
|
<span class="hljs-comment">// variable 's', even temporarily.</span>
|
|
<span class="hljs-comment">//</span>
|
|
<span class="hljs-comment">// The version below, which appears in the third printing, has been</span>
|
|
<span class="hljs-comment">// corrected. To comply with the rules, the bz_stream variable must</span>
|
|
<span class="hljs-comment">// be allocated by C code. We have introduced two C functions,</span>
|
|
<span class="hljs-comment">// bz2alloc and bz2free, to allocate and free instances of the</span>
|
|
<span class="hljs-comment">// bz_stream type. Also, we have changed bz2compress so that before</span>
|
|
<span class="hljs-comment">// it returns, it clears the fields of the bz_stream that contain</span>
|
|
<span class="hljs-comment">// pointers to Go variables.</span>
|
|
</code></pre>
|
|
<p>要使用libbzip2，我們需要先構建一個bz_stream結構體，用於保持輸入和輸出緩存。然後有三個函數：BZ2_bzCompressInit用於初始化緩存，BZ2_bzCompress用於將輸入緩存的數據壓縮到輸出緩存，BZ2_bzCompressEnd用於釋放不需要的緩存。（目前不要擔心包的具體結構, 這個例子的目的就是演示各個部分如何組合在一起的。）</p>
|
|
<p>我們可以在Go代碼中直接調用BZ2_bzCompressInit和BZ2_bzCompressEnd，但是對於BZ2_bzCompress，我們將定義一個C語言的包裝函數，用它完成眞正的工作。下面是C代碼，對應一個獨立的文件。</p>
|
|
<pre><code class="lang-C">gopl.io/ch13/bzip
|
|
|
|
<span class="hljs-comment">/* This file is gopl.io/ch13/bzip/bzip2.c, */</span>
|
|
<span class="hljs-comment">/* a simple wrapper for libbzip2 suitable for cgo. */</span>
|
|
<span class="hljs-preprocessor">#<span class="hljs-keyword">include</span> <span class="hljs-string"><bzlib.h></span></span>
|
|
|
|
<span class="hljs-function"><span class="hljs-keyword">int</span> <span class="hljs-title">bz2compress</span><span class="hljs-params">(bz_stream *s, <span class="hljs-keyword">int</span> action,
|
|
<span class="hljs-keyword">char</span> *in, <span class="hljs-keyword">unsigned</span> *inlen, <span class="hljs-keyword">char</span> *out, <span class="hljs-keyword">unsigned</span> *outlen)</span> </span>{
|
|
s->next_in = in;
|
|
s->avail_in = *inlen;
|
|
s->next_out = out;
|
|
s->avail_out = *outlen;
|
|
<span class="hljs-keyword">int</span> r = BZ2_bzCompress(s, action);
|
|
*inlen -= s->avail_in;
|
|
*outlen -= s->avail_out;
|
|
s->next_in = s->next_out = <span class="hljs-literal">NULL</span>;
|
|
<span class="hljs-keyword">return</span> r;
|
|
}
|
|
</code></pre>
|
|
<p>現在讓我們轉到Go語言部分，第一部分如下所示。其中<code>import "C"</code>的語句是比較特别的。其實併沒有一個叫C的包，但是這行語句會讓Go編譯程序在編譯之前先運行cgo工具。</p>
|
|
<pre><code class="lang-Go"><span class="hljs-comment">// Package bzip provides a writer that uses bzip2 compression (bzip.org).</span>
|
|
<span class="hljs-keyword">package</span> bzip
|
|
|
|
<span class="hljs-comment">/*
|
|
#cgo CFLAGS: -I/usr/include
|
|
#cgo LDFLAGS: -L/usr/lib -lbz2
|
|
#include <bzlib.h>
|
|
#include <stdlib.h>
|
|
bz_stream* bz2alloc() { return calloc(1, sizeof(bz_stream)); }
|
|
int bz2compress(bz_stream *s, int action,
|
|
char *in, unsigned *inlen, char *out, unsigned *outlen);
|
|
void bz2free(bz_stream* s) { free(s); }
|
|
*/</span>
|
|
<span class="hljs-keyword">import</span> <span class="hljs-string">"C"</span>
|
|
|
|
<span class="hljs-keyword">import</span> (
|
|
<span class="hljs-string">"io"</span>
|
|
<span class="hljs-string">"unsafe"</span>
|
|
)
|
|
|
|
<span class="hljs-keyword">type</span> writer <span class="hljs-keyword">struct</span> {
|
|
w io.Writer <span class="hljs-comment">// underlying output stream</span>
|
|
stream *C.bz_stream
|
|
outbuf [<span class="hljs-number">64</span> * <span class="hljs-number">1024</span>]<span class="hljs-typename">byte</span>
|
|
}
|
|
|
|
<span class="hljs-comment">// NewWriter returns a writer for bzip2-compressed streams.</span>
|
|
<span class="hljs-keyword">func</span> NewWriter(out io.Writer) io.WriteCloser {
|
|
<span class="hljs-keyword">const</span> blockSize = <span class="hljs-number">9</span>
|
|
<span class="hljs-keyword">const</span> verbosity = <span class="hljs-number">0</span>
|
|
<span class="hljs-keyword">const</span> workFactor = <span class="hljs-number">30</span>
|
|
w := &writer{w: out, stream: C.bz2alloc()}
|
|
C.BZ2_bzCompressInit(w.stream, blockSize, verbosity, workFactor)
|
|
<span class="hljs-keyword">return</span> w
|
|
}
|
|
</code></pre>
|
|
<p>在預處理過程中，cgo工具爲生成一個臨時包用於包含所有在Go語言中訪問的C語言的函數或類型。例如C.bz_stream和C.BZ2_bzCompressInit。cgo工具通過以某種特殊的方式調用本地的C編譯器來發現在Go源文件導入聲明前的註釋中包含的C頭文件中的內容（譯註：<code>import "C"語句前僅捱着的註釋是對應cgo的特殊語法，對應必要的構建參數選項和C語言代碼</code>）。</p>
|
|
<p>在cgo註釋中還可以包含#cgo指令，用於給C語言工具鏈指定特殊的參數。例如CFLAGS和LDFLAGS分别對應傳給C語言編譯器的編譯參數和鏈接器參數，使它們可以特定目録找到bzlib.h頭文件和libbz2.a庫文件。這個例子假設你已經在/usr目録成功安裝了bzip2庫。如果bzip2庫是安裝在不同的位置，你需要更新這些參數。</p>
|
|
<p>NewWriter函數通過調用C語言的BZ2_bzCompressInit函數來初始化stream中的緩存。在writer結構中還包括了另一個buffer，用於輸出緩存。</p>
|
|
<p>下面是Write方法的實現，返迴成功壓縮數據的大小，主體是一個循環中調用C語言的bz2compress函數實現的。從代碼可以看到，Go程序可以訪問C語言的bz_stream、char和uint類型，還可以訪問bz2compress等函數，甚至可以訪問C語言中像BZ_RUN那樣的宏定義，全部都是以C.x語法訪問。其中C.uint類型和Go語言的uint類型併不相同，卽使它們具有相同的大小也是不同的類型。</p>
|
|
<pre><code class="lang-Go"><span class="hljs-keyword">func</span> (w *writer) Write(data []<span class="hljs-typename">byte</span>) (<span class="hljs-typename">int</span>, error) {
|
|
<span class="hljs-keyword">if</span> w.stream == <span class="hljs-constant">nil</span> {
|
|
<span class="hljs-built_in">panic</span>(<span class="hljs-string">"closed"</span>)
|
|
}
|
|
<span class="hljs-keyword">var</span> total <span class="hljs-typename">int</span> <span class="hljs-comment">// uncompressed bytes written</span>
|
|
|
|
<span class="hljs-keyword">for</span> <span class="hljs-built_in">len</span>(data) > <span class="hljs-number">0</span> {
|
|
inlen, outlen := C.<span class="hljs-typename">uint</span>(<span class="hljs-built_in">len</span>(data)), C.<span class="hljs-typename">uint</span>(<span class="hljs-built_in">cap</span>(w.outbuf))
|
|
C.bz2compress(w.stream, C.BZ_RUN,
|
|
(*C.char)(unsafe.Pointer(&data[<span class="hljs-number">0</span>])), &inlen,
|
|
(*C.char)(unsafe.Pointer(&w.outbuf)), &outlen)
|
|
total += <span class="hljs-typename">int</span>(inlen)
|
|
data = data[inlen:]
|
|
<span class="hljs-keyword">if</span> _, err := w.w.Write(w.outbuf[:outlen]); err != <span class="hljs-constant">nil</span> {
|
|
<span class="hljs-keyword">return</span> total, err
|
|
}
|
|
}
|
|
<span class="hljs-keyword">return</span> total, <span class="hljs-constant">nil</span>
|
|
}
|
|
</code></pre>
|
|
<p>在循環的每次迭代中，向bz2compress傳入數據的地址和剩餘部分的長度，還有輸出緩存w.outbuf的地址和容量。這兩個長度信息通過它們的地址傳入而不是值傳入，因爲bz2compress函數可能會根據已經壓縮的數據和壓縮後數據的大小來更新這兩個值。每個塊壓縮後的數據被寫入到底層的io.Writer。</p>
|
|
<p>Close方法和Write方法有着類似的結構，通過一個循環將剩餘的壓縮數據刷新到輸出緩存。</p>
|
|
<pre><code class="lang-Go"><span class="hljs-comment">// Close flushes the compressed data and closes the stream.</span>
|
|
<span class="hljs-comment">// It does not close the underlying io.Writer.</span>
|
|
<span class="hljs-keyword">func</span> (w *writer) Close() error {
|
|
<span class="hljs-keyword">if</span> w.stream == <span class="hljs-constant">nil</span> {
|
|
<span class="hljs-built_in">panic</span>(<span class="hljs-string">"closed"</span>)
|
|
}
|
|
<span class="hljs-keyword">defer</span> <span class="hljs-keyword">func</span>() {
|
|
C.BZ2_bzCompressEnd(w.stream)
|
|
C.bz2free(w.stream)
|
|
w.stream = <span class="hljs-constant">nil</span>
|
|
}()
|
|
<span class="hljs-keyword">for</span> {
|
|
inlen, outlen := C.<span class="hljs-typename">uint</span>(<span class="hljs-number">0</span>), C.<span class="hljs-typename">uint</span>(<span class="hljs-built_in">cap</span>(w.outbuf))
|
|
r := C.bz2compress(w.stream, C.BZ_FINISH, <span class="hljs-constant">nil</span>, &inlen,
|
|
(*C.char)(unsafe.Pointer(&w.outbuf)), &outlen)
|
|
<span class="hljs-keyword">if</span> _, err := w.w.Write(w.outbuf[:outlen]); err != <span class="hljs-constant">nil</span> {
|
|
<span class="hljs-keyword">return</span> err
|
|
}
|
|
<span class="hljs-keyword">if</span> r == C.BZ_STREAM_END {
|
|
<span class="hljs-keyword">return</span> <span class="hljs-constant">nil</span>
|
|
}
|
|
}
|
|
}
|
|
</code></pre>
|
|
<p>壓縮完成後，Close方法用了defer函數確保函數退出前調用C.BZ2_bzCompressEnd和C.bz2free釋放相關的C語言運行時資源。此刻w.stream指針將不再有效，我們將它設置爲nil以保證安全，然後在每個方法中增加了nil檢測，以防止用戶在關閉後依然錯誤使用相關方法。</p>
|
|
<p>上面的實現中，不僅僅寫是非併發安全的，甚至併發調用Close和Write方法也可能導致程序的的崩潰。脩複這個問題是練習13.3的內容。</p>
|
|
<p>下面的bzipper程序，使用我們自己包實現的bzip2壓縮命令。它的行爲和許多Unix繫統的bzip2命令類似。</p>
|
|
<pre><code class="lang-Go">gopl.io/ch13/bzipper
|
|
|
|
<span class="hljs-comment">// Bzipper reads input, bzip2-compresses it, and writes it out.</span>
|
|
<span class="hljs-keyword">package</span> main
|
|
|
|
<span class="hljs-keyword">import</span> (
|
|
<span class="hljs-string">"io"</span>
|
|
<span class="hljs-string">"log"</span>
|
|
<span class="hljs-string">"os"</span>
|
|
<span class="hljs-string">"gopl.io/ch13/bzip"</span>
|
|
)
|
|
|
|
<span class="hljs-keyword">func</span> main() {
|
|
w := bzip.NewWriter(os.Stdout)
|
|
<span class="hljs-keyword">if</span> _, err := io.Copy(w, os.Stdin); err != <span class="hljs-constant">nil</span> {
|
|
log.Fatalf(<span class="hljs-string">"bzipper: %v\n"</span>, err)
|
|
}
|
|
<span class="hljs-keyword">if</span> err := w.Close(); err != <span class="hljs-constant">nil</span> {
|
|
log.Fatalf(<span class="hljs-string">"bzipper: close: %v\n"</span>, err)
|
|
}
|
|
}
|
|
</code></pre>
|
|
<p>在上面的場景中，我們使用bzipper壓縮了/usr/share/dict/words繫統自帶的詞典，從938,848字節壓縮到335,405字節。大約是原始數據大小的三分之一。然後使用繫統自帶的bunzip2命令進行解壓。壓縮前後文件的SHA256哈希碼是相同了，這也説明了我們的壓縮工具是正確的。（如果你的繫統沒有sha256sum命令，那麽請先按照練習4.2實現一個類似的工具）</p>
|
|
<pre><code>$ go build gopl.io/ch13/bzipper
|
|
$ wc -c < /usr/share/dict/words
|
|
938848
|
|
$ sha256sum < /usr/share/dict/words
|
|
126a4ef38493313edc50b86f90dfdaf7c59ec6c948451eac228f2f3a8ab1a6ed -
|
|
$ ./bzipper < /usr/share/dict/words | wc -c
|
|
335405
|
|
$ ./bzipper < /usr/share/dict/words | bunzip2 | sha256sum
|
|
126a4ef38493313edc50b86f90dfdaf7c59ec6c948451eac228f2f3a8ab1a6ed -
|
|
</code></pre><p>我們演示了如何將一個C語言庫鏈接到Go語言程序。相反, 將Go編譯爲靜態庫然後鏈接到C程序，或者將Go程序編譯爲動態庫然後在C程序中動態加載也都是可行的（譯註：在Go1.5中，Windows繫統的Go語言實現併不支持生成C語言動態庫或靜態庫的特性。不過好消息是，目前已經有人在嚐試解決這個問題，具體請訪問 <a href="https://github.com/golang/go/issues/11058" target="_blank">Issue11058</a> ）。這里我們隻展示的cgo很小的一些方面，更多的關於內存管理、指針、迴調函數、中斷信號處理、字符串、errno處理、終結器，以及goroutines和繫統線程的關繫等，有很多細節可以討論。特别是如何將Go語言的指針傳入C函數的規則也是異常複雜的（譯註：簡單來説，要傳入C函數的Go指針指向的數據本身不能包含指針或其他引用類型；併且C函數在返迴後不能繼續持有Go指針；併且在C函數返迴之前，Go指針是被鎖定的，不能導致對應指針數據被移動或棧的調整），部分的原因在13.2節有討論到，但是在Go1.5中還沒有被明確（譯註：Go1.6將會明確cgo中的指針使用規則）。如果要進一步閲讀，可以從 <a href="https://golang.org/cmd/cgo" target="_blank">https://golang.org/cmd/cgo</a> 開始。</p>
|
|
<p><strong>練習 13.3：</strong> 使用sync.Mutex以保證bzip2.writer在多個goroutines中被併發調用是安全的。</p>
|
|
<p><strong>練習 13.4：</strong> 因爲C庫依賴的限製。 使用os/exec包啟動/bin/bzip2命令作爲一個子進程，提供一個純Go的bzip.NewWriter的替代實現（譯註：雖然是純Go實現，但是運行時將依賴/bin/bzip2命令，其他操作繫統可能無法運行）。</p>
|
|
|
|
|
|
</section>
|
|
|
|
|
|
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</script>
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</body>
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</html>
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