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<a href="/2020/09/11/Linux%E5%86%85%E6%A0%B8-%E5%9F%BA%E7%A1%80%E7%BB%84%E4%BB%B6-%E6%A8%A1%E5%9D%97%E6%9C%BA%E5%88%B6%E5%BF%AB%E9%80%9F%E5%85%A5%E9%97%A81/" class="post-title-link" itemprop="url">Linux内核 / 基础组件 / 模块机制快速入门 (1)</a>
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<span class="post-meta-item-text">发表于</span>
<time title="创建时间：2020-09-11 08:09:28" itemprop="dateCreated datePublished" datetime="2020-09-11T08:09:28+08:00">2020-09-11</time>
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<time title="修改时间：2020-09-21 07:38:55" itemprop="dateModified" datetime="2020-09-21T07:38:55+08:00">2020-09-21</time>
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<p>哈喽，我是杰克吴，继续记录我的学习心得。</p>
<h1 id="一、关于兴趣的几点思考"><a href="#一、关于兴趣的几点思考" class="headerlink" title="一、关于兴趣的几点思考"></a>一、关于兴趣的几点思考</h1><p><strong>1. 享受不是兴趣，愿意付出才是：</strong></p>
<ul>
<li>兴趣很容易跟享受混淆。享受是被动的，无需付出；而兴趣则要求你甘愿为了这件事情付出努力。</li>
</ul>
<p><strong>2.任何事情，接触皮毛的时候不要谈兴趣：</strong></p>
<ul>
<li><p>在我开始公众号写文章之前，只是粗浅地觉得这个事不难我可以尝试一下，而事实上，持续写作的难度和意义超乎大多数人的想象。</p>
</li>
<li><p>任何事情，<strong>先做到 60 分，再谈是否喜欢</strong>。</p>
</li>
</ul>
<p><strong>3. 兴趣和爱好不太一样：</strong></p>
<ul>
<li><p>区别在于你是否需要且愿意通过刻意练习以收获这个兴趣，以及这件事是否能给你带来持续的成就感。</p>
</li>
<li><p>吃喝玩乐(旅游，逛街，买买买)是爱好，不是兴趣。纯粹的看电影是爱好，但是认真地写影评(经历了思考与分享)则算是兴趣。<strong>表面看上去都是同一件事，但是不同人会发展成不一样的结果</strong>。</p>
</li>
<li><p>最开始时可能只是爱好，但是随着你的<strong>持续思考和投入，可能会发展为你的理想职业</strong>。</p>
</li>
</ul>
<p><strong>4. 兴趣可以带有功利性：</strong></p>
<ul>
<li><p>那些看似功利的标准(例如高考、面试)，存在很多偏差的部分，但不可否认，在绝大多数情况下，它们<strong>提供了较为高效和正确的努力方向</strong>。</p>
</li>
<li><p>把自己热爱的事情用来挣钱，非常好。<strong>只凭自己的兴致去做，确实会有更多愉悦，但这也是最廉价、最轻易的喜欢了，问题是，你很难真正做得好</strong>。你真的喜欢这个事，你会主动争取做好，<strong>赢得市场才会给你带来更长久的愉悦感</strong>。</p>
</li>
</ul>
<hr>
<h1 id="二、模块机制快速入门-1"><a href="#二、模块机制快速入门-1" class="headerlink" title="二、模块机制快速入门 (1)"></a>二、模块机制快速入门 (1)</h1><p><strong>目录：</strong></p>
<figure class="highlight angelscript"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 内核模块的使用</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="number">2.</span> 内核模块的文件格式</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="number">3.</span> EXPORT_SYMBOL 是如何实现符号导出的？</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"><span class="number">4.</span> 相关参考</span></pre></td></tr></table></figure>
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<p>哈喽，周二愉快。我是老吴，继续记录我的学习心得。</p>
<h1 id="一、实现目标的价值"><a href="#一、实现目标的价值" class="headerlink" title="一、实现目标的价值"></a>一、实现目标的价值</h1><p><strong>对于实现目标来说，价值有三种来源：</strong></p>
<ul>
<li>成就价值、内在价值和工具价值。</li>
</ul>
<p><strong>某个目标可能有1个或多个价值，以跑步为例：</strong></p>
<ul>
<li><p>有的人跑步，是为了获得自律的标签，跑步里程累计达到成百上千公里，会让他感到骄傲和满足，这是成就价值。</p>
</li>
<li><p>有的人跑步，是享受跑步这件事本身，早晨的阳光或者大汗淋漓都能让人心情愉悦，这是内在价值。</p>
</li>
<li><p>有的人不喜欢跑步，但一直坚持跑步，是因为想要有个好身体以便努力挣钱，这是工具价值。</p>
</li>
</ul>
<p><strong>不同时间同一件事，三种价值的比例会不断变化：</strong></p>
<ul>
<li>某段时间气候特别好，你觉得跑步特别舒服，则是内在价值在起主导作用。</li>
</ul>
<p><strong>思考一下：</strong></p>
<ul>
<li>某些自己想做却一直没开始做的事，是否能通过为其附能上更多的价值以驱使自己开始行动呢？</li>
</ul>
<hr>
<h1 id="二、通知链-notifier-call-chain-快速入门"><a href="#二、通知链-notifier-call-chain-快速入门" class="headerlink" title="二、通知链 ( notifier call chain ) 快速入门"></a>二、通知链 ( notifier call chain ) 快速入门</h1><p><strong>目录：</strong></p>
<figure class="highlight angelscript"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 什么是通知链？</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="number">2.</span> 通知链的内部实现</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="number">3.</span> 如何使用通知链？</span></pre></td></tr></table></figure>
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<a href="/2020/08/29/%E6%AF%8F%E5%A4%A9%E4%B8%80%E7%82%B9C-%E4%B8%80%E4%B8%AA%E4%BC%98%E9%9B%85%E7%9A%84%E5%AD%97%E7%AC%A6%E4%B8%B2%E5%87%BD%E6%95%B0%E5%BA%93/" class="post-title-link" itemprop="url">每天一点 C / 一个优雅的字符串函数库(Simple Dynamic Strings)</a>
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<p>哈喽，周末愉快。我是老吴，继续记录我的学习心得。</p>
<h1 id="一、沉浸式学习"><a href="#一、沉浸式学习" class="headerlink" title="一、沉浸式学习"></a>一、沉浸式学习</h1><p><strong>以学习一门语言为例：</strong><br>大多数人都持有一种观念，要真正学好一门语言必须得去所学语言当地学习或生活一段时间。</p>
<p>而事实上，大多数人都没有这样的学习条件。</p>
<p><strong>解决方法是：</strong><br>自行改造环境，为自己创造沉浸式的学习环境。</p>
<p><strong>例如：</strong></p>
<ul>
<li><p>看新语言的电影;</p>
</li>
<li><p>更改手机、电脑的语言设置;</p>
</li>
<li><p>看新语言的文档和书籍;</p>
</li>
<li><p>用新语言写 todo list;</p>
</li>
<li><p>用新语言来学习自己需要的专业知识;</p>
</li>
<li><p>翻译新语言的文档并分享;</p>
</li>
<li><p>逛所学语言的论坛和网站;</p>
</li>
<li><p>用新语言写代码注释 / commit message / README / issue;</p>
</li>
<li><p>…</p>
</li>
</ul>
<p>对了，我作为英文的爱好者，一直想重启我的英文学习之路，后续想在公众号里记录一些英文相关的知识，请你们不要笑话我<del>~</del></p>
<hr>
<h1 id="二、字符串函数库：Simple-Dynamic-Strings"><a href="#二、字符串函数库：Simple-Dynamic-Strings" class="headerlink" title="二、字符串函数库：Simple Dynamic Strings"></a>二、字符串函数库：Simple Dynamic Strings</h1><h2 id="1-简介"><a href="#1-简介" class="headerlink" title="1. 简介"></a>1. 简介</h2><p>Simple Dynamic Strings (简称 SDS) 是一个 C 语言字符串库，它增强了 C 语言字符串处理的能力。</p>
<p>设计 SDS 原本是为了满足设计者自身日常的 C 编程，后来又被转移到 Redis 中，在 Redis 中被广泛使用并对其进行了修改以适合于高性能操作。 现在，它又被从 Redis 中提取出来的，并 fork 为一个独立项目。</p>
<p>只有 1500 行不到的代码，就能做到 3.2K 个 star，牛牛牛<del>~</del></p>
<p><strong>优点：</strong></p>
<ul>
<li><p>使用更简单;</p>
</li>
<li><p>二进制安全;</p>
</li>
<li><p>效率更高;</p>
</li>
<li><p>与 C 字符串函数兼容;</p>
</li>
</ul>
<p><strong>源码链接：</strong></p>
<figure class="highlight awk"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line">https:<span class="regexp">//gi</span>thub.com<span class="regexp">/antirez/</span>sds</span></pre></td></tr></table></figure>
<p><strong>源码文件：</strong></p>
<figure class="highlight css"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="selector-tag">sds</span><span class="selector-class">.c</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="selector-tag">sdsalloc</span><span class="selector-class">.h</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="selector-tag">sds</span><span class="selector-class">.h</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"><span class="selector-tag">testhelp</span><span class="selector-class">.h</span></span></pre></td></tr></table></figure>
<p><strong>相关 API：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsnewlen</span><span class="params">(<span class="keyword">const</span> <span class="keyword">void</span> *init, <span class="keyword">size_t</span> initlen)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsempty</span><span class="params">(<span class="keyword">void</span>)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsnew</span><span class="params">(<span class="keyword">const</span> <span class="keyword">char</span> *init)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsdup</span><span class="params">(<span class="keyword">const</span> sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">sdsfree</span><span class="params">(sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">sdsupdatelen</span><span class="params">(sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">sdsclear</span><span class="params">(sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">8</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsMakeRoomFor</span><span class="params">(sds s, <span class="keyword">size_t</span> addlen)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">9</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsRemoveFreeSpace</span><span class="params">(sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">10</span></pre></td><td class="code"><pre><span class="line"><span class="function">size_t <span class="title">sdsAllocSize</span><span class="params">(sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">11</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> *<span class="title">sdsAllocPtr</span><span class="params">(sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">12</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">sdsIncrLen</span><span class="params">(sds s, <span class="keyword">ssize_t</span> incr)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">13</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsgrowzero</span><span class="params">(sds s, <span class="keyword">size_t</span> len)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">14</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscatlen</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">void</span> *t, <span class="keyword">size_t</span> len)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">15</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscat</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">char</span> *t)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">16</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscatsds</span><span class="params">(sds s, <span class="keyword">const</span> sds t)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">17</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscpylen</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">char</span> *t, <span class="keyword">size_t</span> len)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">18</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscpy</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">char</span> *t)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">19</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">sdsll2str</span><span class="params">(<span class="keyword">char</span> *s, <span class="keyword">long</span> <span class="keyword">long</span> value)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">20</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">sdsull2str</span><span class="params">(<span class="keyword">char</span> *s, <span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="keyword">long</span> v)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">21</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsfromlonglong</span><span class="params">(<span class="keyword">long</span> <span class="keyword">long</span> value)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">22</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscatvprintf</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">char</span> *fmt, va_list ap)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">23</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscatprintf</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">char</span> *fmt, ...)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">24</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscatfmt</span><span class="params">(sds s, <span class="keyword">char</span> <span class="keyword">const</span> *fmt, ...)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">25</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdstrim</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">char</span> *cset)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">26</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">sdsrange</span><span class="params">(sds s, <span class="keyword">ssize_t</span> start, <span class="keyword">ssize_t</span> <span class="built_in">end</span>)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">27</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">sdstolower</span><span class="params">(sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">28</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">sdstoupper</span><span class="params">(sds s)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">29</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">sdscmp</span><span class="params">(<span class="keyword">const</span> sds s1, <span class="keyword">const</span> sds s2)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">30</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds *<span class="title">sdssplitlen</span><span class="params">(<span class="keyword">const</span> <span class="keyword">char</span> *s, <span class="keyword">ssize_t</span> len, <span class="keyword">const</span> <span class="keyword">char</span> *sep, <span class="keyword">int</span> seplen, <span class="keyword">int</span> *count)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">31</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">sdsfreesplitres</span><span class="params">(sds *tokens, <span class="keyword">int</span> count)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">32</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdscatrepr</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">char</span> *p, <span class="keyword">size_t</span> len)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">33</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">is_hex_digit</span><span class="params">(<span class="keyword">char</span> c)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">34</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">hex_digit_to_int</span><span class="params">(<span class="keyword">char</span> c)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">35</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds *<span class="title">sdssplitargs</span><span class="params">(<span class="keyword">const</span> <span class="keyword">char</span> *<span class="built_in">line</span>, <span class="keyword">int</span> *argc)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">36</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsmapchars</span><span class="params">(sds s, <span class="keyword">const</span> <span class="keyword">char</span> *from, <span class="keyword">const</span> <span class="keyword">char</span> *to, <span class="keyword">size_t</span> setlen)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">37</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsjoin</span><span class="params">(<span class="keyword">char</span> **argv, <span class="keyword">int</span> argc, <span class="keyword">char</span> *sep)</span> </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">38</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsjoinsds</span><span class="params">(sds *argv, <span class="keyword">int</span> argc, <span class="keyword">const</span> <span class="keyword">char</span> *sep, <span class="keyword">size_t</span> seplen)</span></span></span></pre></td></tr></table></figure>
<h2 id="2-比较常用的功能"><a href="#2-比较常用的功能" class="headerlink" title="2. 比较常用的功能"></a>2. 比较常用的功能</h2><h3 id="2-1-创建字符串"><a href="#2-1-创建字符串" class="headerlink" title="2.1 创建字符串"></a>2.1 创建字符串</h3><p><strong>sdsnew() 和 sdsfree()：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string"><stdio.h></span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">"sds.h"</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">"sdsalloc.h"</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"> sds mystr = sdsnew(<span class="string">"Hello World!"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">8</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s\n"</span>, mystr);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">9</span></pre></td><td class="code"><pre><span class="line"> sdsfree(mystr);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">10</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> gcc -o sdsdemo sds.c sdsdemo.c</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line">Hello World!</span></pre></td></tr></table></figure>
<p>看到了吗？</p>
<p>printf 直接就可以打印 sds，这就是说 sds 本身就是 C 语言的字符串类型。</p>
<p><strong>sds 的定义如下：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="keyword">char</span> *sds;</span></pre></td></tr></table></figure>
<p>也就是说，sds 是能兼容 libc 里字符串处理函数 (例如strcpy, strcat…)的。</p>
<p>当不再使用 sds 字符串时，就是是空串，也要通过 sdsfree 销毁字符串。</p>
<h3 id="2-2-获取字符串长度"><a href="#2-2-获取字符串长度" class="headerlink" title="2.2 获取字符串长度"></a>2.2 获取字符串长度</h3><p><strong>sdsnewlen()：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">char</span> buf[<span class="number">3</span>];</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> sds mystring;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"> buf[<span class="number">0</span>] = <span class="string">'A'</span>;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"> buf[<span class="number">1</span>] = <span class="string">'B'</span>;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">8</span></pre></td><td class="code"><pre><span class="line"> buf[<span class="number">2</span>] = <span class="string">'C'</span>;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">9</span></pre></td><td class="code"><pre><span class="line"> mystring = sdsnewlen(buf,<span class="number">3</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">10</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s of len %d\n"</span>, mystring, (<span class="keyword">int</span>) sdslen(mystring));</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">11</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">ABC of len 3</span></pre></td></tr></table></figure>
<p><strong>和 strlen() 有 2 点不同</strong>：</p>
<ul>
<li><p>运行时长固定，sds 内部有数据结构保存着字符串的长度;</p>
</li>
<li><p>长度与字符串内是否有 NULL 无关;</p>
</li>
</ul>
<h3 id="2-3-拼接字符串"><a href="#2-3-拼接字符串" class="headerlink" title="2.3 拼接字符串"></a>2.3 拼接字符串</h3><p><strong>sdscat()：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> sds s = sdsempty();</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> s = sdscat(s, <span class="string">"Hello "</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> s = sdscat(s, <span class="string">"World!"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s\n"</span>, s);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">Hello World!</span></pre></td></tr></table></figure>
<p>sdscat 接受的参数是以 NULL 结尾的字符串，如果想摆脱这个限制，可以用 sdscatsds()。</p>
<p><strong>sdscatsds()：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> sds s1 = sdsnew(<span class="string">"aaa"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> sds s2 = sdsnew(<span class="string">"bbb"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> s1 = sdscatsds(s1,s2);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"> sdsfree(s2);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s\n"</span>, s1);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">8</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">aaabbb</span></pre></td></tr></table></figure>
<h3 id="2-4-扩展字符串长度"><a href="#2-4-扩展字符串长度" class="headerlink" title="2.4 扩展字符串长度"></a>2.4 扩展字符串长度</h3><p><strong>sdsgrowzero()：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> sds s = sdsnew(<span class="string">"Hello"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> s = sdsgrowzero(s,<span class="number">6</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> s[<span class="number">5</span>] = <span class="string">'!'</span>; <span class="comment">/* We are sure this is safe*/</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s\n"</span>, s);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">Hello!</span></pre></td></tr></table></figure>
<h3 id="2-5-格式化字符串"><a href="#2-5-格式化字符串" class="headerlink" title="2.5 格式化字符串"></a>2.5 格式化字符串</h3><p><strong>sdscatprintf()：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> sds s;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">int</span> a = <span class="number">10</span>, b = <span class="number">20</span>;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> s = sdsnew(<span class="string">"The sum is: "</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"> s = sdscatprintf(s,<span class="string">"%d+%d = %d"</span>,a,b,a+b);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s\n"</span>, s);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">8</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">The sum is: 10+20 = 30</span></pre></td></tr></table></figure>
<h3 id="2-6-截取字符串"><a href="#2-6-截取字符串" class="headerlink" title="2.6 截取字符串"></a>2.6 截取字符串</h3><p><strong>sdstrim()：去掉指定字符</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> sds s = sdsnew(<span class="string">" my string\n\n "</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> sdstrim(s,<span class="string">" \n"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"-%s-\n"</span>,s);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">-my string-</span></pre></td></tr></table></figure>
<p>去掉了空格和换行符。</p>
<p><strong>sdsrange()：截取指定范围内的字符串</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> sds s = sdsnew(<span class="string">"Hello World!"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> sdsrange(s,<span class="number">1</span>,<span class="number">4</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"-%s-\n"</span>， s);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">-ello-</span></pre></td></tr></table></figure>
<h3 id="2-7-字符串分割-Tokenization"><a href="#2-7-字符串分割-Tokenization" class="headerlink" title="2.7 字符串分割 (Tokenization)"></a>2.7 字符串分割 (Tokenization)</h3><p><strong>sdssplitlen() 和 sdsfreesplitres()：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> sds *tokens;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">int</span> count, j;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"> sds <span class="built_in">line</span> = sdsnew(<span class="string">"Hello World!"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"> tokens = sdssplitlen(<span class="built_in">line</span>, sdslen(<span class="built_in">line</span>),<span class="string">" "</span>,<span class="number">1</span>,&count);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">8</span></pre></td><td class="code"><pre><span class="line"></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">9</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">for</span> (j = <span class="number">0</span>; j < count; j++)</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">10</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s\n"</span>, tokens[j]);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">11</span></pre></td><td class="code"><pre><span class="line"> sdsfreesplitres(tokens,count);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">12</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p>sdssplitlen() 第 3和4 个参数指定分割符为空格。</p>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">Hello</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line">World!</span></pre></td></tr></table></figure>
<h3 id="2-8-字符串合并-String-joining"><a href="#2-8-字符串合并-String-joining" class="headerlink" title="2.8 字符串合并 (String joining)"></a>2.8 字符串合并 (String joining)</h3><p><strong>sdssplitlen() 和 sdsfreesplitres()：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">void</span>)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"></span>{</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">char</span> *tokens[<span class="number">3</span>] = {<span class="string">"foo"</span>,<span class="string">"bar"</span>,<span class="string">"zap"</span>};</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> sds s = sdsjoin(tokens, <span class="number">3</span>, <span class="string">"|"</span>);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">printf</span>(<span class="string">"%s\n"</span>, s);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line">}</span></pre></td></tr></table></figure>
<p><strong>运行效果：</strong></p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="meta">$</span><span class="bash"> ./sdsdemo</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">foo|bar|zap</span></pre></td></tr></table></figure>
<p>还有其他一些功能，用到再研究吧！</p>
<h2 id="3-简单了解一下内部实现"><a href="#3-简单了解一下内部实现" class="headerlink" title="3. 简单了解一下内部实现"></a>3. 简单了解一下内部实现</h2><p>在 SDSD 中，使用二进制前缀(头部) 来保存字符串相关的信息，该头部存储在 SDS 返回给用户的字符串的实际指针之前：</p>
<figure class="highlight asciidoc"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="code">+--------+</span>-------------------------------<span class="code">+-----------+</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">| Header | Binary safe C alike string... | Null term |</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="code">+--------+</span>-------------------------------<span class="code">+-----------+</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"><span class="code"> |</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"><span class="code"> `-> Pointer returned to the user.</span></span></pre></td></tr></table></figure>
<p>这个 Header 在代码中用结构体来描述，该结构体定义大致如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">sdshdr</span> {</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"> [...]</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">int</span> len;</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">char</span> buf[];</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line">};</span></pre></td></tr></table></figure>
<ul>
<li><p>len 存储的是字符串长度;</p>
</li>
<li><p>buf 指向紧随其后的字符串首地址;</p>
</li>
</ul>
<p>假设你使用的字符串为 “HELLOWORLD”，为了提升效率，SDS 可能会提前分配多一些空间，所以实际的内存布局如下：</p>
<figure class="highlight jboss-cli"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line">+<span class="params">------------</span>+<span class="params">------------------------</span>+<span class="params">-----------</span>+<span class="params">---------------</span>\</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line">| len | buf | H E L L O W O R L D \n | Null term | Free space \</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line">+<span class="params">------------</span>+<span class="params">------------------------</span>+<span class="params">-----------</span>+<span class="params">---------------</span>\</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> |</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> `-> Pointer returned to the user.</span></pre></td></tr></table></figure>
<p><strong>现在，我们来看一下 SDS 分配字符串的大致步骤：</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="function">sds <span class="title">sdsnew</span><span class="params">(<span class="keyword">const</span> <span class="keyword">char</span> *init)</span></span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="function"> initlen </span>= (init == <span class="literal">NULL</span>) ? <span class="number">0</span> : <span class="built_in">strlen</span>(init);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"> sdsnewlen(init, initlen);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">int</span> hdrlen = sdsHdrSize(type); <span class="comment">// 确定 Header 的长度</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> sh = s_malloc(hdrlen+initlen+<span class="number">1</span>); <span class="comment">// 分配 Header + String + 1 个字节的空间</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"> s = (<span class="keyword">char</span>*)sh+hdrlen; <span class="comment">// 保存 C string 的地址</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">8</span></pre></td><td class="code"><pre><span class="line"> SDS_HDR_VAR(<span class="number">8</span>,s); <span class="comment">// 定义 struct sdshdr sh</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">9</span></pre></td><td class="code"><pre><span class="line"> sh->len = initlen; <span class="comment">// 初始化 struct sdshdr sh</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">10</span></pre></td><td class="code"><pre><span class="line"></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">11</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">if</span> (initlen && init) <span class="comment">// 初始化 C string </span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">12</span></pre></td><td class="code"><pre><span class="line"> <span class="built_in">memcpy</span>(s, init, initlen);</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">13</span></pre></td><td class="code"><pre><span class="line"> </span></pre></td></tr><tr><td class="gutter"><pre><span class="line">14</span></pre></td><td class="code"><pre><span class="line"> s[initlen] = <span class="string">'\0'</span>; <span class="comment">// 总是添加一个 NULL</span></span></pre></td></tr><tr><td class="gutter"><pre><span class="line">15</span></pre></td><td class="code"><pre><span class="line"> <span class="keyword">return</span> s; <span class="comment">// 返回 C string</span></span></pre></td></tr></table></figure>
<p>其他的 SDS API 是如何实现的，就留给大家自行分析了。</p>
<h2 id="4-相关参考"><a href="#4-相关参考" class="headerlink" title="4. 相关参考"></a>4. 相关参考</h2><p>-《Linux程序设计》，6，7.1 章节</p>
<p>-《C primer plus》，11，12 章节</p>
<p>-《C 和指针》，9 章节</p>
<p>-《Linux 系统边城》，9 章节</p>
<p>-《C专家编程》，7.5 章节</p>
<p>-《C和C++程序员面试秘笈》，4 章节</p>
<hr>
<h1 id="三、思考技术，也要思考人生"><a href="#三、思考技术，也要思考人生" class="headerlink" title="三、思考技术，也要思考人生"></a>三、思考技术，也要思考人生</h1><p><strong>学习技术，更要学习如何生活</strong>。</p>
<p>你和我各有一个苹果，如果我们交换苹果的话，我们还是只有一个苹果。但当你和我各有一个想法，我们交换想法的话，我们就都有两个想法了。</p>
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<p>对 <strong>嵌入式系统 (Linux、RTOS、OpenWrt、Android) 和 开源软件</strong> 感兴趣，想和更多人互相交流学习，请关注公众号：<strong>嵌入式Hacker</strong>。</p>
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<h1 id="一、进步的滞后性"><a href="#一、进步的滞后性" class="headerlink" title="一、进步的滞后性"></a>一、进步的滞后性</h1><p><strong>我们期望进步是线性：</strong><br>每一个人付出一些努力后，都希望它有立竿见影的效果。</p>
<p><strong>现实是：</strong><br>做出努力后，结果的显现往往滞后。</p>
<p>只有在几个月或几年后，我们才意识到以前学习/工作的真正价值。</p>
<p><strong>“失望谷地” 的出现：</strong><br>人们在投入数周或数月的辛勤工作后，却没有任何看得见的效果，于是进入深感沮丧的时期。</p>
<p><strong>如何改变：</strong><br>1> 改变意识。功夫并没有白费，它只是蓄积起来了。直到很久以后，以前努力的全部价值才会显露出来。</p>
<p>2> 寻找一些可以帮助自己对抗滞后进步所带来的低落情绪的技巧。例如培养习惯的四大定律，具体的如即时奖励、习惯追踪等。</p>
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<h1 id="二、triggerhappy-源码分析-3-select-的应用"><a href="#二、triggerhappy-源码分析-3-select-的应用" class="headerlink" title="二、triggerhappy 源码分析 / 3.select() 的应用"></a>二、triggerhappy 源码分析 / 3.select() 的应用</h1><p><strong>正文目录：</strong></p>
<figure class="highlight angelscript"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> thd.c / process_events() 源码分析</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="number">2.</span> I/O 多路复用 ( Multiplexing ) 是为了解决什么问题</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="number">3.</span> I/O 多路复用设计思路</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"><span class="number">4.</span> select() 的用法</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"><span class="number">5.</span> 和 poll/epoll 对比(补充知识，非重点)</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"><span class="number">6.</span> triggerhappy：thd.c / process_devices() 源码分析</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"><span class="number">7.</span> 相关参考</span></pre></td></tr></table></figure>
<p><strong>写作目的：</strong></p>
<ul>
<li>通过阅读 triggerhappy 的源码，学习 I/O 多路复用的方法之一 select() 的使用方法。</li>
</ul>
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<p>哈喽，我是老吴，继续记录我的学习心得。</p>
<h1 id="一、保持专注的几个技巧"><a href="#一、保持专注的几个技巧" class="headerlink" title="一、保持专注的几个技巧"></a>一、保持专注的几个技巧</h1><ul>
<li><p>将最重要的事放在早上做。</p>
</li>
<li><p>待在无干扰环境下，比如图书馆。</p>
</li>
<li><p>意识到刚坐下开始投入工作前，有点负面小情绪是特别正常的现象。</p>
</li>
<li><p>让“开心一刻”成为计划的一部分。</p>
</li>
<li><p>拥有合情合理的日计划和周计划。</p>
</li>
</ul>
<hr>
<h1 id="二、Linux-字符设备驱动内幕-1"><a href="#二、Linux-字符设备驱动内幕-1" class="headerlink" title="二、Linux 字符设备驱动内幕 (1)"></a>二、Linux 字符设备驱动内幕 (1)</h1><p><strong>正文目录：</strong></p>
<figure class="highlight angelscript"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 什么是字符设备驱动？</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="number">2.</span> 快速体验字符设备驱动和应用程序 (超简单的 demo)</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="number">3.</span> 字符设备在内核里的抽象</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"> <span class="number">3.1</span> 字符设备核心代码概览</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"> <span class="number">3.2</span> 对字符设备进行抽象: struct cdev</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"> <span class="number">3.3</span> 对字符设备的操作进行抽象：struct file_operations</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"><span class="number">4.</span> 更多值得学习的知识点</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">8</span></pre></td><td class="code"><pre><span class="line"><span class="number">5.</span> 相关参考</span></pre></td></tr></table></figure>
<p><strong>写作目的：</strong></p>
<ul>
<li>探索 Linux 字符设备驱动。</li>
</ul>
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<p>哈喽，我是老吴，今天分享一点小经验。</p>
<h1 id="一、个人玩家，如何判断一块开发板好坏？"><a href="#一、个人玩家，如何判断一块开发板好坏？" class="headerlink" title="一、个人玩家，如何判断一块开发板好坏？"></a>一、个人玩家，如何判断一块开发板好坏？</h1><ol>
<li><strong>了解 cpu 原厂的综合实力，谷歌一下就能看到全球各大半导体公司的排名</strong>。一般来说，无论是代码质量，文档资料，还是技术支持，外企的芯片会比国产芯片好，唯一的缺点就是价格更贵，但这对个人玩家来说是无所谓的。对于一款 cpu，一般就买一个板子。这样的话，1 个芯片的溢价最多就 100~200 块，<strong>但是对于带来的品味提升和学习难度的下降，以及后续带来的求职竞争力的提升(前提是你投入了时间去学习)，这点小钱不值得一提，这笔投资性价比超高</strong>。</li>
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<p>哈喽，我是老吴，继续记录我的学习心得。</p>
<h1 id="一、能力错觉"><a href="#一、能力错觉" class="headerlink" title="一、能力错觉"></a>一、能力错觉</h1><p>当书本（或谷歌）摆在眼前时，大脑会产生错觉，以为学习材料也同样存入了大脑，阅读毕竟比回想简单多了。</p>
<p><strong>以为反复的阅读资料就是自己已经掌握知识，这就是能力错觉</strong>。</p>
<p><strong>解决能力错觉的方法</strong>: </p>
<ul>
<li>积极回想——让大脑提取关键概念，而非通过重复阅读被动地获取知识，这样才能高效地学习。</li>
</ul>
<p><strong>现在网络上盛行各种it类的视频教程，我不否认不少视频教程是高质量的，但是所有视频类资料都有一个问题</strong>: </p>
<ul>
<li>可以让人不用阅读书籍，减少思考，只要被动地听老师们讲课就能舒舒服服地获取到知识，这很容易会让某些初级的软件开发人员形成能力错觉，仿佛视频里写过的代码，解决过的 bug 都是自己已经学到的知识似的。</li>
</ul>
<p><strong>有效的解决办法是</strong>： </p>
<ul>
<li><p>公开学习笔记和练习代码。公开学习笔记的目的是借助外部压力，高效回想，进而提高自己的学习标准。</p>
</li>
<li><p>另外，公开写作则会给你的写作增加很多维度的外部压力，你会想如何让别人更好地理解我要表达的意思；如何传递更多价值，让别人读完有所收获；如何让更多人看到；如何让别人读得下去；如何排版让大家看得更舒服；</p>
</li>
</ul>
<hr>
<h1 id="二、数组和指针有什么区别？"><a href="#二、数组和指针有什么区别？" class="headerlink" title="二、数组和指针有什么区别？"></a>二、数组和指针有什么区别？</h1><p><strong>正文目录：</strong></p>
<figure class="highlight angelscript"><table><tr><td class="gutter"><pre><span class="line">1</span></pre></td><td class="code"><pre><span class="line"><span class="number">1.</span> 用于声明时两者有重大区别</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">2</span></pre></td><td class="code"><pre><span class="line"><span class="number">2.</span> 你真的理解声明和定义吗？</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">3</span></pre></td><td class="code"><pre><span class="line"><span class="number">3.</span> 数组和指针的底层是如何访问数据的？</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">4</span></pre></td><td class="code"><pre><span class="line"><span class="number">4.</span> 哪些场景可以用指针代替数组？</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">5</span></pre></td><td class="code"><pre><span class="line"><span class="number">5.</span> 为什么C语言要把数组形参退化为指针？</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">6</span></pre></td><td class="code"><pre><span class="line"><span class="number">6.</span> 如何使用指针访问多维数组？</span></pre></td></tr><tr><td class="gutter"><pre><span class="line">7</span></pre></td><td class="code"><pre><span class="line"><span class="number">7.</span> 相关面试题</span></pre></td></tr></table></figure>
<p><strong>写作目的：</strong></p>
<ul>
<li>正确看待数组和指针。</li>
</ul>
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