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朝花夕拾.html
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<title>朝花夕拾</title></head><body><h2>一. c宏</h2>
<ol>
<li>
<p><code class="notranslate">do{}while(0)</code> 宏的用处?</p>
<p>避免调用者出现使用错误，保证程序执行的一致性。<br>
例如：</p>
<div class="highlight highlight-source-c"><pre class="notranslate"><span class="pl-k">#define</span> <span class="pl-en">FOO</span>() foo1();foo2();</pre></div>
<p>调用代码：</p>
<div class="highlight highlight-source-c"><pre class="notranslate"><span class="pl-k">if</span> (<span class="pl-s1">a</span> <span class="pl-c1">></span> <span class="pl-c1">0</span>)
<span class="pl-en">FOO</span>();</pre></div>
<p>会被扩展成:</p>
<div class="highlight highlight-source-c"><pre class="notranslate"><span class="pl-k">if</span> (<span class="pl-s1">a</span> <span class="pl-c1">></span> <span class="pl-c1">0</span>)
<span class="pl-en">foo1</span>();<span class="pl-en">foo2</span>();</pre></div>
<p>这时就产生了一个问题，若是<code class="notranslate">a <= 0</code>，<code class="notranslate">foo2()</code>仍然会被调用。<br>
正确的写法：</p>
<div class="highlight highlight-source-c"><pre class="notranslate"><span class="pl-k">#define</span> <span class="pl-en">FOO</span>() \
do{ \
foo1(); \
foo2(); \
}while(0)</pre></div>
</li>
</ol>
<h2>二. 计算机二三事</h2>
<ol>
<li>
<p>栈和堆的区别</p>
<ul>
<li>栈的结构是先进后出，永远操作的是栈顶</li>
<li>栈中的数据必须已知且大小固定（如c语言的数组）</li>
<li>堆是缺乏组织的，当向堆中放入数据，操作系统会去寻找到一块足够大的空间，标记为已使用，并返回一个指向这块空间的指针</li>
</ul>
<p>操作栈空间是比堆速度快的，因为使用堆你需要先寻找到一块足够大的空间（<code class="notranslate">malloc</code>），而且使用的内存并不是连续的（如动态链表），需要在内存中跳来跳去，这些操作都会降低性能。<br>
还有很多原因，如cpu对栈有直接支持（<code class="notranslate">push</code>, <code class="notranslate">pop</code>）；栈内存由操作系统管理，而堆内存由用户程序管理。</p>
</li>
<li>
<p>指针</p>
<blockquote>
<p>In computer science, a pointer is a programming language object that stores a memory address. --wikipedia</p>
</blockquote>
<p>在计算机科学中，指针就是存储了一个内存地址的编程语言对象。</p>
</li>
<li>
<p>引用</p>
<p>以 java 为例:</p>
<blockquote>
<p>A reference is an address that indicates where an object's variables and methods are stored.</p>
</blockquote>
<p>引用是一个指向了对象的方法和变量存储位置的地址。</p>
</li>
</ol>
<h2>三. linux命令</h2>
<ol>
<li>
<p>删除当前目录除某文件外的所有文件</p>
<div class="highlight highlight-source-shell"><pre class="notranslate">ls <span class="pl-k">|</span> grep -v except_filename <span class="pl-k">|</span> xargs rm -rf</pre></div>
</li>
<li>
<p>更新所有的module</p>
<pre class="notranslate"><code class="notranslate">git submodule update --init --recursive --remote
</code></pre>
</li>
</ol>
<h2>四. Redis需要注意的问题</h2>
<ol>
<li>集群环境下使用lua脚本只支持一个key，多个key需要用{}括起来</li>
</ol><hr><p>Thu Feb 17 10:27:30 2022</p><script src="https://utteranc.es/client.js"
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