mirror of
https://github.com/gopl-zh/gopl-zh.github.com.git
synced 2025-12-17 11:14:20 +08:00
reduce file size
This commit is contained in:
chai2010
@@ -25,10 +25,6 @@
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<body>
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<div class="book" data-level="13.1" data-chapter-title="unsafe.Sizeof, Alignof 和 Offsetof" data-filepath="ch13/ch13-01.md" data-basepath=".." data-revision="Thu Dec 24 2015 14:42:02 GMT+0800 (中国标准时间)">
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<div class="book" data-level="13.1" data-chapter-title="unsafe.Sizeof, Alignof 和 Offsetof" data-filepath="ch13/ch13-01.md" data-basepath=".." data-revision="Fri Dec 25 2015 12:32:44 GMT+0800 (中国标准时间)">
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@@ -2132,14 +2128,6 @@ Sizeof(x.c) = 24 Alignof(x.c) = 8 Offsetof(x.c) = 8
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<script src="../gitbook/app.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-search/lunr.min.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-search/search.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-sharing/buttons.js"></script>
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@@ -2149,7 +2137,7 @@ Sizeof(x.c) = 24 Alignof(x.c) = 8 Offsetof(x.c) = 8
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<script>
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require(["gitbook"], function(gitbook) {
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var config = {"highlight":{},"search":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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var config = {"highlight":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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gitbook.start(config);
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});
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-search/search.css">
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<body>
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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="Thu Dec 24 2015 14:42:02 GMT+0800 (中国标准时间)">
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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="Fri Dec 25 2015 12:32:44 GMT+0800 (中国标准时间)">
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<div class="book-summary">
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@@ -2061,7 +2057,7 @@ pb := (*<span class="hljs-typename">int16</span>)(unsafe.Pointer(tmp))
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</code></pre>
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<p>這里併沒有指針引用<code>new</code>新創建的變量，因此該語句執行完成之後，垃圾收集器有權馬上迴收其內存空間，所以返迴的pT將是無效的地址。</p>
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<p>雖然目前的Go語言實現還沒有使用移動GC（譯註：未來可能實現），但這不該是編寫錯誤代碼僥幸的理由：當前的Go語言實現已經有移動變量的場景。在5.2節我們提到goroutine的棧是根據需要動態增長的。當發送棧動態增長的時候，原來棧中的所以變量可能需要被移動到新的更大的棧中，所以我們併不能確保變量的地址在整個使用週期內是不變的。</p>
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<p>在編寫本文時，還沒有清晰的原則來指引Go程序員，什麽樣的unsafe.Pointer和uintptr的轉換是不安全的（參考 [Go issue7192](<a href="https://github.com/golang/go/issues/7192" target="_blank">https://github.com/golang/go/issues/7192</a> ）. 譯註: 該問題已經關閉），因此我們強烈建議按照最壞的方式處理。將所有包含變量地址的uintptr類型變量當作BUG處理，同時減少不必要的unsafe.Pointer類型到uintptr類型的轉換。在第一個例子中，有三個轉換——字段偏移量到uintptr的轉換和轉迴unsafe.Pointer類型的操作——所有的轉換全在一個表達式完成。</p>
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<p>在編寫本文時，還沒有清晰的原則來指引Go程序員，什麽樣的unsafe.Pointer和uintptr的轉換是不安全的（參考 <a href="https://github.com/golang/go/issues/7192" target="_blank">Issue7192</a> ）. 譯註: 該問題已經關閉），因此我們強烈建議按照最壞的方式處理。將所有包含變量地址的uintptr類型變量當作BUG處理，同時減少不必要的unsafe.Pointer類型到uintptr類型的轉換。在第一個例子中，有三個轉換——字段偏移量到uintptr的轉換和轉迴unsafe.Pointer類型的操作——所有的轉換全在一個表達式完成。</p>
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<p>當調用一個庫函數，併且返迴的是uintptr類型地址時（譯註：普通方法實現的函數不盡量不要返迴該類型。下面例子是reflect包的函數，reflect包和unsafe包一樣都是采用特殊技術實現的，編譯器可能給它們開了後門），比如下面反射包中的相關函數，返迴的結果應該立卽轉換爲unsafe.Pointer以確保指針指向的是相同的變量。</p>
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<pre><code class="lang-Go"><span class="hljs-keyword">package</span> reflect
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@@ -2091,14 +2087,6 @@ pb := (*<span class="hljs-typename">int16</span>)(unsafe.Pointer(tmp))
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<script src="../gitbook/app.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-search/lunr.min.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-search/search.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-sharing/buttons.js"></script>
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@@ -2108,7 +2096,7 @@ pb := (*<span class="hljs-typename">int16</span>)(unsafe.Pointer(tmp))
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<script>
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require(["gitbook"], function(gitbook) {
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var config = {"highlight":{},"search":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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var config = {"highlight":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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gitbook.start(config);
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});
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</script>
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-search/search.css">
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<body>
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<div class="book" data-level="13.3" data-chapter-title="示例: 深度相等判斷" data-filepath="ch13/ch13-03.md" data-basepath=".." data-revision="Thu Dec 24 2015 14:42:02 GMT+0800 (中国标准时间)">
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<div class="book" data-level="13.3" data-chapter-title="示例: 深度相等判斷" data-filepath="ch13/ch13-03.md" data-basepath=".." data-revision="Fri Dec 25 2015 12:32:44 GMT+0800 (中国标准时间)">
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<div class="book-summary">
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@@ -2149,14 +2145,6 @@ fmt.Println(Equal(a, c)) <span class="hljs-comment">// "false"</span>
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<script src="../gitbook/app.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-search/lunr.min.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-search/search.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-sharing/buttons.js"></script>
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@@ -2166,7 +2154,7 @@ fmt.Println(Equal(a, c)) <span class="hljs-comment">// "false"</span>
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<script>
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require(["gitbook"], function(gitbook) {
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var config = {"highlight":{},"search":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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var config = {"highlight":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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gitbook.start(config);
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});
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</script>
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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 24 2015 14:42:02 GMT+0800 (中国标准时间)">
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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="Fri Dec 25 2015 12:32:44 GMT+0800 (中国标准时间)">
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<div class="book-summary">
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@@ -2159,7 +2155,7 @@ void bz2free(bz_stream* s) { free(s); }
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}
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}
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</code></pre>
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<p>壓縮完成後，Close方法用了defer函數確保函數退齣前調用C.BZ2_bzCompressEnd和C.bz2free釋放相關的C資源。此刻w.stream指針將不在有效，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>
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<p>壓縮完成後，Close方法用了defer函數確保函數退齣前調用C.BZ2_bzCompressEnd和C.bz2free釋放相關的C语言运行时資源。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>
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<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>
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<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>
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<pre><code class="lang-Go">gopl.io/ch13/bzipper
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@@ -2196,7 +2192,7 @@ $ ./bzipper < /usr/share/dict/words | bunzip2 | sha256sum
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126a4ef38493313edc50b86f90dfdaf7c59ec6c948451eac228f2f3a8ab1a6ed -
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</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>
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<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>
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<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目録，其他操作繫統可能無法運行）。</p>
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<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>
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</section>
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@@ -2219,14 +2215,6 @@ $ ./bzipper < /usr/share/dict/words | bunzip2 | sha256sum
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<script src="../gitbook/app.js"></script>
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|
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<script src="../gitbook/plugins/gitbook-plugin-search/lunr.min.js"></script>
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<script src="../gitbook/plugins/gitbook-plugin-search/search.js"></script>
|
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|
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<script src="../gitbook/plugins/gitbook-plugin-sharing/buttons.js"></script>
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||||
@@ -2236,7 +2224,7 @@ $ ./bzipper < /usr/share/dict/words | bunzip2 | sha256sum
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<script>
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require(["gitbook"], function(gitbook) {
|
||||
var config = {"highlight":{},"search":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
|
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var config = {"highlight":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
|
||||
gitbook.start(config);
|
||||
});
|
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</script>
|
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@@ -25,10 +25,6 @@
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-search/search.css">
|
||||
|
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-fontsettings/website.css">
|
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@@ -48,7 +44,7 @@
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<body>
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<div class="book" data-level="13.5" data-chapter-title="幾點忠告" data-filepath="ch13/ch13-05.md" data-basepath=".." data-revision="Thu Dec 24 2015 14:42:02 GMT+0800 (中国标准时间)">
|
||||
<div class="book" data-level="13.5" data-chapter-title="幾點忠告" data-filepath="ch13/ch13-05.md" data-basepath=".." data-revision="Fri Dec 25 2015 12:32:44 GMT+0800 (中国标准时间)">
|
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|
||||
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||||
<div class="book-summary">
|
||||
@@ -2051,14 +2047,6 @@
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<script src="../gitbook/app.js"></script>
|
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<script src="../gitbook/plugins/gitbook-plugin-search/lunr.min.js"></script>
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|
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|
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<script src="../gitbook/plugins/gitbook-plugin-search/search.js"></script>
|
||||
|
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<script src="../gitbook/plugins/gitbook-plugin-sharing/buttons.js"></script>
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@@ -2068,7 +2056,7 @@
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||||
<script>
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require(["gitbook"], function(gitbook) {
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var config = {"highlight":{},"search":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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var config = {"highlight":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
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gitbook.start(config);
|
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});
|
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</script>
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@@ -25,10 +25,6 @@
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-search/search.css">
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<link rel="stylesheet" href="../gitbook/plugins/gitbook-plugin-fontsettings/website.css">
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@@ -48,7 +44,7 @@
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<body>
|
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<div class="book" data-level="13" data-chapter-title="底層編程" data-filepath="ch13/ch13.md" data-basepath=".." data-revision="Thu Dec 24 2015 14:42:02 GMT+0800 (中国标准时间)">
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<div class="book" data-level="13" data-chapter-title="底層編程" data-filepath="ch13/ch13.md" data-basepath=".." data-revision="Fri Dec 25 2015 12:32:44 GMT+0800 (中国标准时间)">
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|
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<div class="book-summary">
|
||||
@@ -2055,14 +2051,6 @@
|
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<script src="../gitbook/app.js"></script>
|
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<script src="../gitbook/plugins/gitbook-plugin-search/lunr.min.js"></script>
|
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|
||||
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||||
|
||||
<script src="../gitbook/plugins/gitbook-plugin-search/search.js"></script>
|
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|
||||
|
||||
|
||||
<script src="../gitbook/plugins/gitbook-plugin-sharing/buttons.js"></script>
|
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|
||||
@@ -2072,7 +2060,7 @@
|
||||
|
||||
<script>
|
||||
require(["gitbook"], function(gitbook) {
|
||||
var config = {"highlight":{},"search":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
|
||||
var config = {"highlight":{},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2}};
|
||||
gitbook.start(config);
|
||||
});
|
||||
</script>
|
||||
|
||||
Reference in New Issue
Block a user