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atom.xml
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<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<title><![CDATA[Alvin]]></title>
<link href="http://freealvin.github.io/atom.xml" rel="self"/>
<link href="http://freealvin.github.io/"/>
<updated>2015-04-13T02:09:06+08:00</updated>
<id>http://freealvin.github.io/</id>
<author>
<name><![CDATA[Alvin]]></name>
</author>
<generator uri="http://octopress.org/">Octopress</generator>
<entry>
<title type="html"><![CDATA[Java参数传递]]></title>
<link href="http://freealvin.github.io/blog/2015/04/13/javacan-shu-chuan-di/"/>
<updated>2015-04-13T01:55:00+08:00</updated>
<id>http://freealvin.github.io/blog/2015/04/13/javacan-shu-chuan-di</id>
<content type="html"><![CDATA[<p>参数传递分为值传递和引用传递，Java是面向对象的编程语言，又是如何传递参数的呢？</p>
<!--more-->
<p>Java的值传递和其他语言的类似，没有什么特别的，这里主要介绍对象作为参数的传递。对象作为参数，传递的是对象的引用吗？其实不是。</p>
<p>先面给出一个例子</p>
<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kd">public</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">swap</span><span class="o">(</span><span class="n">Employee</span> <span class="n">x</span><span class="o">,</span> <span class="n">Employee</span> <span class="n">y</span><span class="o">)</span>
</span><span class='line'><span class="o">{</span>
</span><span class='line'> <span class="n">Employee</span> <span class="n">temp</span> <span class="o">=</span> <span class="n">x</span><span class="o">;</span>
</span><span class='line'> <span class="n">x</span> <span class="o">=</span> <span class="n">y</span><span class="o">;</span>
</span><span class='line'> <span class="n">y</span> <span class="o">=</span> <span class="n">temp</span><span class="o">;</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<p>如果Java对对象采用的是引用调用，那么这个方法就能实现交换数据的效果：</p>
<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="n">Employee</span> <span class="n">a</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Employee</span><span class="o">(</span><span class="s">"alvin"</span><span class="o">);</span>
</span><span class='line'><span class="n">Employee</span> <span class="n">b</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Employee</span><span class="o">(</span><span class="s">"nathan"</span><span class="o">);</span>
</span><span class='line'><span class="n">swap</span><span class="o">(</span><span class="n">a</span><span class="o">,</span><span class="n">b</span><span class="o">);</span>
</span></code></pre></td></tr></table></div></figure>
<p>结果会是a变成nathan， b变成alvin吗？最终的结果并没有变化，a仍为alvin，b也仍为nathan。</p>
<p>这个过程说明，Java采用的不是引用调用。实际上，对象引用进行的是<bold>值传递</bold>。</p>
<p>下面总结一下：</p>
<pre><code>1. 方法不能修改一个基本数据类型的参数
2. 方法可以改变对象参数的状态
3. 方法不能对对象参数引用一个新对象。
</code></pre>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Java 类的final引用成员实例]]></title>
<link href="http://freealvin.github.io/blog/2015/04/11/java-lei-de-finalyin-yong-cheng-yuan-shi-li/"/>
<updated>2015-04-11T08:32:47+08:00</updated>
<id>http://freealvin.github.io/blog/2015/04/11/java-lei-de-finalyin-yong-cheng-yuan-shi-li</id>
<content type="html"><![CDATA[<p>final修饰符大都用于基本类型，或不可变类的域（如果类中的每个方法都不会改变其对象，这种类就是不可变的类。例如，String类就是一个不可变的类）。对于可变的类使用final修饰符可能会对读者造成混乱。例如，private final Date hiredate；</p>
<p>仅仅意味着存储在hiredate变量中的<em>对象引用</em>在对象构造之后不能被改变，而不意味着hiredate对象是一个常量。任何方法都可以对hiredate引用的对象调用setTime更改器。</p>
<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
<span class='line-number'>12</span>
<span class='line-number'>13</span>
<span class='line-number'>14</span>
<span class='line-number'>15</span>
<span class='line-number'>16</span>
<span class='line-number'>17</span>
<span class='line-number'>18</span>
<span class='line-number'>19</span>
<span class='line-number'>20</span>
<span class='line-number'>21</span>
<span class='line-number'>22</span>
<span class='line-number'>23</span>
<span class='line-number'>24</span>
<span class='line-number'>25</span>
<span class='line-number'>26</span>
<span class='line-number'>27</span>
<span class='line-number'>28</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kn">package</span> <span class="n">per</span><span class="o">.</span><span class="na">alvin</span><span class="o">.</span><span class="na">demos</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'><span class="kd">public</span> <span class="kd">class</span> <span class="nc">User</span> <span class="o">{</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">private</span> <span class="n">String</span> <span class="n">name</span><span class="o">;</span>
</span><span class='line'> <span class="kd">private</span> <span class="kt">int</span> <span class="n">age</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="nf">User</span><span class="o">(){</span>
</span><span class='line'>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="kd">public</span> <span class="nf">User</span><span class="o">(</span><span class="n">String</span> <span class="n">name</span><span class="o">,</span> <span class="kt">int</span> <span class="n">age</span><span class="o">){</span>
</span><span class='line'> <span class="k">this</span><span class="o">.</span><span class="na">name</span> <span class="o">=</span> <span class="n">name</span><span class="o">;</span>
</span><span class='line'> <span class="k">this</span><span class="o">.</span><span class="na">age</span> <span class="o">=</span> <span class="n">age</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="n">String</span> <span class="nf">getName</span><span class="o">()</span> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">name</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="kd">public</span> <span class="kt">void</span> <span class="nf">setName</span><span class="o">(</span><span class="n">String</span> <span class="n">name</span><span class="o">)</span> <span class="o">{</span>
</span><span class='line'> <span class="k">this</span><span class="o">.</span><span class="na">name</span> <span class="o">=</span> <span class="n">name</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="kd">public</span> <span class="kt">int</span> <span class="nf">getAge</span><span class="o">()</span> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">age</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="kd">public</span> <span class="kt">void</span> <span class="nf">setAge</span><span class="o">(</span><span class="kt">int</span> <span class="n">age</span><span class="o">)</span> <span class="o">{</span>
</span><span class='line'> <span class="k">this</span><span class="o">.</span><span class="na">age</span> <span class="o">=</span> <span class="n">age</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<figure class='code'><figcaption><span></span></figcaption><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
<span class='line-number'>12</span>
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<span class='line-number'>19</span>
<span class='line-number'>20</span>
<span class='line-number'>21</span>
<span class='line-number'>22</span>
</pre></td><td class='code'><pre><code class='java'><span class='line'><span class="kn">package</span> <span class="n">per</span><span class="o">.</span><span class="na">alvin</span><span class="o">.</span><span class="na">demos</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'><span class="kd">public</span> <span class="kd">class</span> <span class="nc">Item</span> <span class="o">{</span>
</span><span class='line'> <span class="kd">private</span> <span class="kd">final</span> <span class="n">User</span> <span class="n">user</span><span class="o">;</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="nf">Item</span><span class="o">(</span><span class="n">User</span> <span class="n">user</span><span class="o">){</span>
</span><span class='line'> <span class="k">this</span><span class="o">.</span><span class="na">user</span> <span class="o">=</span> <span class="n">user</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'> <span class="kd">public</span> <span class="n">User</span> <span class="nf">getUser</span><span class="o">()</span> <span class="o">{</span>
</span><span class='line'> <span class="k">return</span> <span class="n">user</span><span class="o">;</span>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'>
</span><span class='line'> <span class="kd">public</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">main</span><span class="o">(</span><span class="n">String</span> <span class="o">[]</span> <span class="n">arags</span><span class="o">){</span>
</span><span class='line'> <span class="n">User</span> <span class="n">alvin</span> <span class="o">=</span> <span class="k">new</span> <span class="n">User</span><span class="o">(</span><span class="s">"alvin"</span><span class="o">,</span> <span class="mi">22</span><span class="o">);</span>
</span><span class='line'> <span class="n">Item</span> <span class="n">item</span> <span class="o">=</span> <span class="k">new</span> <span class="n">Item</span><span class="o">(</span><span class="n">alvin</span><span class="o">);</span>
</span><span class='line'>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">item</span><span class="o">.</span><span class="na">getUser</span><span class="o">().</span><span class="na">getName</span><span class="o">());</span>
</span><span class='line'> <span class="n">alvin</span><span class="o">.</span><span class="na">setName</span><span class="o">(</span><span class="s">"nathan"</span><span class="o">);</span>
</span><span class='line'> <span class="n">System</span><span class="o">.</span><span class="na">out</span><span class="o">.</span><span class="na">println</span><span class="o">(</span><span class="n">item</span><span class="o">.</span><span class="na">getUser</span><span class="o">().</span><span class="na">getName</span><span class="o">());</span>
</span><span class='line'>
</span><span class='line'> <span class="o">}</span>
</span><span class='line'><span class="o">}</span>
</span></code></pre></td></tr></table></div></figure>
<p></p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Unix环境高级编程之进程环境]]></title>
<link href="http://freealvin.github.io/blog/2015/04/08/unixhuan-jing-gao-ji-bian-cheng-zhi-jin-cheng-huan-jing/"/>
<updated>2015-04-08T19:30:59+08:00</updated>
<id>http://freealvin.github.io/blog/2015/04/08/unixhuan-jing-gao-ji-bian-cheng-zhi-jin-cheng-huan-jing</id>
<content type="html"><![CDATA[<p>当执行程序时，main函数是如何被调用的；命令行参数如何传送给程序；典型的存储器布局是什么样的；如何分配额外的存储空间；进程如何使用环境变量；不同进程的终止形式。</p>
<!--more--->
<h2>main函数</h2>
<p>当内核执行C程序时，在调用main前先调用一个特殊的启动例程。可执行文件将词启动例程指定微程序的起始位置——这由连接编辑器设置，而连接编辑器由C编译器调用，启动例程从内核获得命令行参数和环境变量。</p>
<h2>进程终止</h2>
<p>八种方式可以终止进程，5种为正常终止，它们是：
1.从main返回
2.调用exit
3.调用<em>exit或</em>EXIT
4.最后一个线程从其启动例程返回
5.最后一个线程调用pthread_exit</p>
<p>异常的终止方式有三种
6.调用abort
7.接到一个信号并终止
8.最后一个线程对取消请求做出相应</p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[六个月后]]></title>
<link href="http://freealvin.github.io/blog/2015/04/04/liu-ge-yue-hou/"/>
<updated>2015-04-04T17:08:13+08:00</updated>
<id>http://freealvin.github.io/blog/2015/04/04/liu-ge-yue-hou</id>
<content type="html"><![CDATA[<p>六个月后重新找回Octopress开始写作的我，开始知道自己的未来的目标，精通java，阅读Mysql类的书，开始去真正了解分布式系统设计，向我的同学学习，了解机器学习。</p>
<p>我知道现在白天实习，晚上去抽时间学习比较累，但有目标的人心里总是有底的，我相信我能坚持。加油。</p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[C语言的缩进和空白]]></title>
<link href="http://freealvin.github.io/blog/2013/12/02/cyu-yan-de-suo-jin-he-kong-bai/"/>
<updated>2013-12-02T21:31:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/12/02/cyu-yan-de-suo-jin-he-kong-bai</id>
<content type="html"><![CDATA[<p>C语言的缩进和空白使用原则</p>
<!--more-->
<h1>一般编码缩进规则</h1>
<p>1.字if、while、for与其后的控制表达式的(括号之间插入一个空格分隔，但括号内的表达式应紧贴括号
例如
<code> while (1) </code>
2.双目运算符的两侧各插入一个空格分隔，单目运算符和操作数之间不加空格
例如：
<code>i␣=␣i␣+␣1、++i、!(i␣<␣1)、-x、&a[1]等)</code></p>
<p>3.后缀运算符和操作数之间也不加空格
例如:
取结构体成员<code>s.a</code>、函数调用<code>foo(arg1)</code>、取数组成员<code>a[i]</code></p>
<ol>
<li><p>,号和;号之后要加空格，这是英文的书写习惯
例如：
<code>for␣(i␣=␣1;␣i␣<␣10;␣i++)、foo(arg1,␣arg2)</code></p></li>
<li><p>有时候为了突出优先级也可以写得更紧凑一些
例如：
<code>for␣(i=1;␣i<10;␣i++)</code>、<code>distance␣=␣sqrt(x<em>x␣+␣y</em>y)</code>等。但是省略的空格一定不要误导了读代码的人，例如<code>a||b␣&&␣c</code>很容易让人理解成错误的优先级.</p></li>
<li><p>接近或大于80个字符的较长语句要折行写
由于UNIX系统标准的字符终端是24行80列的，接近或大于80个字符的较长语句要折行写，折行后用空格和上面的表达式或参数对齐，例如：</p></li>
</ol>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>if␣(sqrt(x*x␣+␣y*y)␣>␣5.0
</span><span class='line'> &&␣x␣<␣0.0
</span><span class='line'> &&␣y␣>␣0.0)</span></code></pre></td></tr></table></div></figure>
<p>再比如：</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>foo(sqrt(x*x␣+␣y*y),
</span><span class='line'> a[i-1]␣+␣b[i-1]␣+␣c[i-1])</span></code></pre></td></tr></table></div></figure>
<ol>
<li>较长的字符串可以断成多个字符串然后分行书写
例如:</li>
</ol>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>printf("This is such a long sentence that "
</span><span class='line'> "it cannot be held within a line\n");</span></code></pre></td></tr></table></div></figure>
<p>C编译器会自动把相邻的多个字符串接在一起，以上两个字符串相当于一个字符串”This is such a long sentence that it cannot be held within a line\n”。</p>
<ol>
<li>在变量定义语句中用Tab字符，使变量名对齐
有的人喜欢在变量定义语句中用Tab字符，使变量名对齐，这样看起来很美观。</li>
</ol>
<h1>内核编码缩进规则</h1>
<p>1.要用缩进体现出语句块的层次关系
要用缩进体现出语句块的层次关系，使用Tab字符缩进，不能用空格代替Tab。在标准的字符终端上一个Tab看起来是8个空格的宽度，如果你的文本编辑器可以设置Tab的显示宽度是几个空格，建议也设成8，这样大的缩进使代码看起来非常清晰。如果有的行用空格做缩进，有的行用Tab做缩进，甚至空格和Tab混用，那么一旦改变了文本编辑器的Tab显示宽度就会看起来非常混乱，所以内核代码风格规定只能用Tab做缩进，不能用空格代替Tab。</p>
<ol>
<li>语句块的{或}应该和关键字写在同一行，用空格隔开，而不是单独占一行
if/else、while、do/while、for、switch这些可以带语句块的语句，语句块的{或}应该和关键字写在同一行，用空格隔开，而不是单独占一行。例如应该这样写：</li>
</ol>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>if␣(...)␣{
</span><span class='line'> →语句列表
</span><span class='line'>}␣else␣if␣(...)␣{
</span><span class='line'> →语句列表
</span><span class='line'>}</span></code></pre></td></tr></table></div></figure>
<p>但很多人习惯这样写：</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>if␣(...)
</span><span class='line'>{
</span><span class='line'> →语句列表
</span><span class='line'>}
</span><span class='line'>else␣if␣(...)
</span><span class='line'>{
</span><span class='line'> →语句列表
</span><span class='line'>}</span></code></pre></td></tr></table></div></figure>
<p>内核的写法和[K&R]一致，好处是不必占太多行，使得一屏能显示更多代码。这两种写法用得都很广泛，只要在同一个项目中能保持统一就可以了。</p>
<ol>
<li>函数定义的{和}单独占一行，这一点和语句块的规定不同</li>
</ol>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>int␣foo(int␣a,␣int␣b)
</span><span class='line'>{
</span><span class='line'> →语句列表
</span><span class='line'>}</span></code></pre></td></tr></table></div></figure>
<ol>
<li>switch和语句块里的case、default对齐写
switch和语句块里的case、default对齐写，也就是说语句块里的case、default标号相对于switch不往里缩进，但标号下的语句要往里缩进。例如：</li>
</ol>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>→switch␣(c)␣{
</span><span class='line'>→case 'A':
</span><span class='line'>→ →语句列表
</span><span class='line'>→case 'B':
</span><span class='line'>→ →语句列表
</span><span class='line'>→default:
</span><span class='line'>→ →语句列表
</span><span class='line'>→}</span></code></pre></td></tr></table></div></figure>
<p>用于goto语句的自定义标号应该顶头写不缩进，而不管标号下的语句缩进到第几层。</p>
<ol>
<li>代码中每个逻辑段落之间应该用一个空行分隔开
例如每个函数定义之间应该插入一个空行，头文件、全局变量定义和函数定义之间也应该插入空行，例如：</li>
</ol>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
<span class='line-number'>12</span>
<span class='line-number'>13</span>
<span class='line-number'>14</span>
<span class='line-number'>15</span>
<span class='line-number'>16</span>
<span class='line-number'>17</span>
<span class='line-number'>18</span>
<span class='line-number'>19</span>
<span class='line-number'>20</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>#include <stdio.h>
</span><span class='line'>#include <stdlib.h>
</span><span class='line'>
</span><span class='line'>int g;
</span><span class='line'>double h;
</span><span class='line'>
</span><span class='line'>int foo(void)
</span><span class='line'>{
</span><span class='line'> →语句列表
</span><span class='line'>}
</span><span class='line'>
</span><span class='line'>int bar(int a)
</span><span class='line'>{
</span><span class='line'> →语句列表
</span><span class='line'>}
</span><span class='line'>
</span><span class='line'>int main(void)
</span><span class='line'>{
</span><span class='line'> →语句列表
</span><span class='line'>}</span></code></pre></td></tr></table></div></figure>
<ol>
<li>一个函数的语句列表如果很长，也可以根据相关性分成若干组，用空行分隔。
一个函数的语句列表如果很长，也可以根据相关性分成若干组，用空行分隔。这条规定不是严格要求，通常把变量定义组成一组，后面加空行，return语句之前加空行，例如：</li>
</ol>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>int main(void)
</span><span class='line'>{
</span><span class='line'> →int →a, b;
</span><span class='line'> →double →c;
</span><span class='line'>
</span><span class='line'> →语句组1
</span><span class='line'>
</span><span class='line'> →语句组2
</span><span class='line'>
</span><span class='line'> →return 0;
</span><span class='line'>}</span></code></pre></td></tr></table></div></figure>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[AT&T汇编语法2]]></title>
<link href="http://freealvin.github.io/blog/2013/12/02/at-and-thui-bian-yu-fa-2/"/>
<updated>2013-12-02T08:45:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/12/02/at-and-thui-bian-yu-fa-2</id>
<content type="html"><![CDATA[<ol>
<li>内联汇编</li>
</ol>
<!--more-->
<p>（一）内联汇编
参考<a href="http://www.ibm.com/developerworks/cn/linux/sdk/assemble/inline/">Linux中x86的内联汇编</a></p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>asm (assembler template
</span><span class='line'>
</span><span class='line'> : output operands (optional)
</span><span class='line'> : input operands (optional)
</span><span class='line'> : list of clobbered registers
</span><span class='line'> (optional)
</span><span class='line'>);</span></code></pre></td></tr></table></div></figure>
<p> 汇编程序模板由汇编指令组成。输入操作数是充当指令输入操作数使用的 C 表达式。输出操作数是将对其执行汇编指令输出的 C 表达式。</p>
<h2>内敛汇编的基本要素</h2>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>{
</span><span class='line'> int a=10, b;
</span><span class='line'> asm ("movl %1, %%eax;
</span><span class='line'> movl %%eax, %0;"
</span><span class='line'> :"=r"(b) /* output */
</span><span class='line'> :"r"(a) /* input */
</span><span class='line'> :"%eax"); /* clobbered register */
</span><span class='line'>}</span></code></pre></td></tr></table></div></figure>
<p>·”b”是输出操作数,由%0引用,“a”是输入操作数,由%1引用<br/>
·”r”是操作数的约束,它指定将变量”a”和”b”存储在寄存器中。输出操作数约束应该带有一个约束修饰符”=“,表示它是输出操作数<br/>
·要在”asm”内使用寄存器%eax,%eax的前面应该再加一个%,换句话说是%%eax，因为”asm”使用%0、%1等来表示变量。任何带有一个%的数都看做是输入/输出操作数,而不认为是寄存器<br/>
·第三个冒号后的修饰寄存器%eax告诉将在asm中修改GCC%eax的值，这样GCC就不适用该寄存器存储任何其它的值<br/>
·movl %1, %%eax将”a”的值移到%eax中, movl %%eax, %0将%eax的内容移到”b”中<br/>
·因为”b”被指定成输出操作数,因此当”asm”的执行完成后，它将反映出更新的值。换句话说,对”asm”内”b”所做的更改将在”asm”外反映出来</p>
<h2>汇编程序模板</h2>
<p>汇编程序模板是一组插入到 C 程序中的汇编指令（可以是单个指令，也可以是一组指令）。每条指令都应该由双引号括起，或者整组指令应该由双引号括起。每条指令还应该用一个定界符结尾。有效的定界符为新行 (\n) 和分号 (;)。 ‘\n’ 后可以跟一个 tab(\t) 作为格式化符号，增加 GCC 在汇编文件中生成的指令的可读性。 指令通过数 %0、%1 等来引用 C 表达式（指定为操作数）。</p>
<p>如果希望确保编译器不会在 “asm” 内部优化指令，可以在 “asm” 后使用关键字 “volatile”。如果程序必须与 ANSI C 兼容，则应该使用 <strong>asm</strong> 和 <strong>volatile</strong>，而不是 asm 和 volatile</p>
<h2>操作数</h2>
<p>C 表达式用作 “asm” 内的汇编指令操作数。在汇编指令通过对 C 程序的 C 表达式进行操作来执行有意义的作业的情况下，操作数是内联汇编的主要特性。</p>
<p>每个操作数都由操作数约束字符串指定，后面跟用括弧括起的 C 表达式，例如：”constraint” (C expression)。操作数约束的主要功能是确定操作数的寻址方式。</p>
<p>可以在输入和输出部分中同时使用多个操作数。每个操作数由逗号分隔开。</p>
<p>在汇编程序模板内部，操作数由数字引用。如果总共有 n 个操作数（包括输入和输出），那么第一个输出操作数的编号为 0，逐项递增，最后那个输入操作数的编号为 n -1。总操作数的数目限制在 10，如果机器描述中任何指令模式中的最大操作数数目大于 10，则使用后者作为限制。</p>
<h2>修饰寄存器列表</h2>
<p>如果 “asm” 中的指令指的是硬件寄存器，可以告诉 GCC 我们将自己使用和修改它们。这样，GCC 就不会假设它装入到这些寄存器中的值是有效值。通常不需要将输入和输出寄存器列为 clobbered，因为 GCC 知道 “asm” 使用它们（因为它们被明确指定为约束）。不过，如果指令使用任何其它的寄存器，无论是明确的还是隐含的（寄存器不在输入约束列表中出现，也不在输出约束列表中出现），寄存器都必须被指定为修饰列表。修饰寄存器列在第三个冒号之后，其名称被指定为字符串。</p>
<p>至于关键字，如果指令以某些不可预知且不明确的方式修改了内存，则可能将 “memory” 关键字添加到修饰寄存器列表中。这样就告诉 GCC 不要在不同指令之间将内存值高速缓存在寄存器中。</p>
<h2>操作数约束</h2>
<p>前面提到过，”asm” 中的每个操作数都应该由操作数约束字符串描述，后面跟用括弧括起的 C 表达式。操作数约束主要是确定指令中操作数的寻址方式。约束也可以指定：
1. 是否允许操作数位于寄存器中，以及它可以包括在哪些种类的寄存器中
2. 操作数是否可以是内存引用，以及在这种情况下使用哪些种类的地址
3. 操作数是否可以是立即数
约束还要求两个操作数匹配。</p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[AT&T汇编语言学习1]]></title>
<link href="http://freealvin.github.io/blog/2013/11/27/at-and-thui-bian-yu-yan-xue-xi-1/"/>
<updated>2013-11-27T09:14:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/11/27/at-and-thui-bian-yu-yan-xue-xi-1</id>
<content type="html"><![CDATA[<!--more-->
<h1>一. AT&T汇编语法格式</h1>
<p>(1) 寄存器引用</p>
<pre><code>引用寄存器要在寄存器号前加%，如move %eax, %ebx
</code></pre>
<p>(2) 操作数顺序</p>
<pre><code>操作数排列是从源（左）到目的（右）， 如
</code></pre>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>move %eax, %ebx
</span><span class='line'># %eax为源, %ebx为目的地址</span></code></pre></td></tr></table></div></figure>
<p>(3) 常数/立即数的格式<br/></p>
<pre><code>使用立即数，要在数前加$，如mov $4, %ebx
符号常数直接引用 如mov value, %ebx
引用符号地址在符号前加$，如mov $value, %ebx
</code></pre>
<p>(4) 操作数的长度<br/></p>
<pre><code>操作数的长度用加在指令后的符号表示
b(byte)
w(word)
l(long)
如：mov w%ax, %bx
</code></pre>
<h1>二. 转移和调用</h1>
<p>
(1) 在AT&T汇编格式中，绝对转移和调用指令(jmp/call)的操作数前 要加上’*‘作为前缀<br/>
(2) 远转移指令和远调用指令的操作码，在AT&T汇编格式中为”ljump”和”lcall”,在Itel汇编格式中则为”jmp far”和”call far”<br/></p>
<p>AT&T格式</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>ljump $section, $offset
</span><span class='line'>lcall $section, $offset</span></code></pre></td></tr></table></div></figure>
<p>Intel格式</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>jump far section:offset
</span><span class='line'>call far section:offset</span></code></pre></td></tr></table></div></figure>
<p>(3) 远程返回指令<br/></p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>lret $stack_adjust
</span><span class='line'>ret far stack_adjust</span></code></pre></td></tr></table></div></figure>
<p>(4) 寻址方式<br/></p>
<pre><code>用section:disp(base, index, scale)表示，计算方法是:
base + index*scale + disp
section:[base+index*scale+disp] #Intel
</code></pre>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>movl -4(%ebp), %eax mov eax, [ebp-4]
</span><span class='line'>movl array(, %eax, 4), %eax mov eax, [eax*4+array]
</span><span class='line'>movw array(%ebx, %eax, 4), %cx mov cx, [ebx+4*eax+array]
</span><span class='line'>movb $4, %fs:(%eax) mov fs:eax, 4</span></code></pre></td></tr></table></div></figure>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Linux中的正则表达式]]></title>
<link href="http://freealvin.github.io/blog/2013/11/26/linuxzhong-de-zheng-ze-biao-da-shi/"/>
<updated>2013-11-26T20:09:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/11/26/linuxzhong-de-zheng-ze-biao-da-shi</id>
<content type="html"><![CDATA[<!--more about 正则表达式-->
<h1>正则表达式</h1>
<br />
<pre><code>正则表达式完成字符串的匹配搜索，在Unix系统中，sed、grep、vi等工具都是用regexp规则。
(1) 正则表达式的基本语法
| 符号 | 含义 | 举例 | 匹配 |
| --------------- | ---------------------------------------- | -------------------- | -------------------------- |
| . | 任何字符 | a.. | a后面有两个字符的字符串 |
| ? | 修饰匹配次数，0次或1次 | x? | 0个或1个x |
| ^ | 匹配行首 | ^word | 位于行首的word |
| + | 重复一次或多次 | y+ | 一个--或多个连续的y |
| $ | 行尾 | x$ | 以x结尾的行 |
| * | 重复0次或多次 | w.*s | 以w开头、s结尾的任何字符串 |
| [字符表] | 字符表中的任一字符 | [tT] | 小写字母t或大写字母T |
| [!字符表] | 匹配不属于范围指定内的字符 | [!a-z] | 匹配不是小写字母的字符 |
| [^字符表] | 任一不在字符表中的字符 | [^a-z A-Z] | 任何非字母 |
| \ | 转义字符 | \\n | 匹配换行符 |
| \{min,max\} | 前导正则表达式最少重复min次，最多重复max次 | x\{1,5\} | 最少1个最多5个x |
| \(...\) | 将圆括号中匹配的字符串存储到下一个寄存器中 | \(more\)and\1 | 匹配more and more |
| 表达式|1表达式2 | 匹配表达式1或表达式2 | hello| happy | 匹配hello或happy |
</code></pre>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Ruby on Rails With Mongodb]]></title>
<link href="http://freealvin.github.io/blog/2013/11/18/ruby-on-rails-with-mongodb/"/>
<updated>2013-11-18T00:35:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/11/18/ruby-on-rails-with-mongodb</id>
<content type="html"><![CDATA[
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[把cs50.h添加到库中]]></title>
<link href="http://freealvin.github.io/blog/2013/10/11/ba-cs50-dot-htian-jia-dao-ku-zhong/"/>
<updated>2013-10-11T23:25:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/10/11/ba-cs50-dot-htian-jia-dao-ku-zhong</id>
<content type="html"><![CDATA[<p> 我最近在看网易公开课CS50，自我感觉非常喜欢David J. Malan的教学方法，非常羡慕和感慨哈佛学生的大学学习环境。也感谢网易为广大中国学生带来的福利。</p>
<p> 以下是自己网上搜素总结的如何模仿搭建CS50中Malan使用的开发环境。</p>
<p> <!--more-->
1. 参考<a href="https://manual.cs50.net/library/"> CS50 Manual</a>，选择适合自己的安装方法
我的是Centos，所以执行以下命令，安装cs50库</p>
<pre><code><div class='bogus-wrapper'><notextile><figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
</code></pre>
<p><span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
<span class='line-number'>9</span>
<span class='line-number'>10</span>
<span class='line-number'>11</span>
<span class='line-number'>12</span>
<span class='line-number'>13</span>
<span class='line-number'>14</span>
<span class='line-number'>15</span>
</pre></td><td class='code'><pre><code class=''><span class='line'>yum -y install gcc
</span><span class='line'> wget <a href="http://mirror.cs50.net/library50/c/library50-c-5.zip">http://mirror.cs50.net/library50/c/library50-c-5.zip</a>
</span><span class='line'> unzip library50-c-5.zip
</span><span class='line'> rm -f library50-c-5.zip
</span><span class='line'> cd library50-c-5
</span><span class='line'> gcc -c -ggdb -std=c99 cs50.c -o cs50.o
</span><span class='line'> ar rcs libcs50.a cs50.o
</span><span class='line'> chmod 0644 cs50.h libcs50.a
</span><span class='line'> mkdir -p /usr/local/include
</span><span class='line'> chmod 0755 /usr/local/include
</span><span class='line'> mv -f cs50.h /usr/local/include
</span><span class='line'> mkdir -p /usr/local/lib
</span><span class='line'> chmod 0755 /usr/local/lib
</span><span class='line'> mv -f libcs50.a /usr/local/lib
</span><span class='line'> rm -rf library50-c-5</span></code></pre></td></tr></table></div></figure></notextile></div>
2. 安装完cs50库后, 修改make选项</p>
<pre><code>修改~/.bashrc文件
在文件末尾添加
</code></pre>
<p> <figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
</pre></td><td class='code'><pre><code class=''><span class='line'># configure gcc
</span><span class='line'> export CC=gcc
</span><span class='line'> export CFLAGS=“-ggdb -std=c99 -Wall -Werror -Wformat=0”
</span><span class='line'> export LANG=C
</span><span class='line'> export LDLIBS=“-lcs50 -lm”
</span><span class='line'> alias gcc=“gcc $CFLAGS”</span></code></pre></td></tr></table></div></figure>
3. 执行source ~/.bashrc使更改后的bashrc文件生效</p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[递归与分治策略之整数划分]]></title>
<link href="http://freealvin.github.io/blog/2013/09/18/di-gui-yu-fen-zhi-ce-lue-zhi-zheng-shu-hua-fen/"/>
<updated>2013-09-18T10:49:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/09/18/di-gui-yu-fen-zhi-ce-lue-zhi-zheng-shu-hua-fen</id>
<content type="html"><![CDATA[<p> 将正整数划分为一些列正整数之和。在正整数n的所有不同的划分中，将最大加数n1不大于m的划分个数记为q(n, m).可以建立q(n, m)的递归关系。</p>
<!--more-->
<ol>
<li> q(n,1) = 1, n>=1</li>
<li> q(n,m) = q(n,n) m>=n</li>
<li> q(n,n) = 1+q(n,n-1)</li>
<li> q(n,m) = q(n, n-1)+q(n-m, m), n>m>1：正整数n的最大加数不大于m的划分可以分成最大加数为m的划分和最大加数小于等于m-1的划分。</li>
</ol>
<p>有递归关系可以写出递归函数。</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
<span class='line-number'>8</span>
</pre></td><td class='code'><pre><code class='cpp'><span class='line'><span class="kt">int</span> <span class="nf">q</span><span class="p">(</span><span class="kt">int</span> <span class="n">n</span><span class="p">,</span> <span class="kt">int</span> <span class="n">m</span><span class="p">)</span>
</span><span class='line'><span class="p">{</span>
</span><span class='line'> <span class="k">if</span><span class="p">(</span><span class="n">n</span><span class="o"><</span><span class="mi">1</span><span class="o">||</span><span class="n">m</span><span class="o"><</span><span class="mi">1</span><span class="p">)</span> <span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
</span><span class='line'> <span class="k">if</span><span class="p">(</span><span class="n">n</span><span class="o">==</span><span class="mi">1</span><span class="o">||</span><span class="n">m</span><span class="o">==</span><span class="mi">1</span><span class="p">)</span> <span class="k">return</span> <span class="mi">1</span><span class="p">;</span>
</span><span class='line'> <span class="k">if</span><span class="p">(</span><span class="n">n</span><span class="o"><</span><span class="n">m</span><span class="p">)</span> <span class="k">return</span> <span class="n">q</span><span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="n">n</span><span class="p">);</span>
</span><span class='line'> <span class="k">if</span><span class="p">(</span><span class="n">n</span><span class="o">==</span><span class="n">m</span><span class="p">)</span> <span class="k">return</span> <span class="mi">1</span><span class="o">+</span><span class="n">q</span><span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="n">n</span><span class="o">-</span><span class="mi">1</span><span class="p">);</span>
</span><span class='line'> <span class="k">return</span> <span class="n">q</span><span class="p">(</span><span class="n">n</span><span class="p">,</span> <span class="n">m</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span><span class="o">+</span><span class="n">q</span><span class="p">(</span><span class="n">n</span><span class="o">-</span><span class="n">m</span><span class="p">,</span> <span class="n">m</span><span class="p">);</span>
</span><span class='line'><span class="p">}</span>
</span></code></pre></td></tr></table></div></figure>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[如何从零开始学会 Ruby on Rails]]></title>
<link href="http://freealvin.github.io/blog/2013/08/28/ru-he-cong-ling-kai-shi-xue-hui-ruby-on-rails/"/>
<updated>2013-08-28T15:53:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/08/28/ru-he-cong-ling-kai-shi-xue-hui-ruby-on-rails</id>
<content type="html"><![CDATA[<!--more-->
<p>来自<a href="http://huacnlee.com/blog/how-to-start-learning-ruby-on-rails/">http://huacnlee.com/blog/how-to-start-learning-ruby-on-rails/</a>
以下步骤请一步一步来，切勿心急跳过，最好连我上面的链接都不要提前点击！
1.安装 Linux 或 Mac， 开发工具使用 Windows & Linux –> Sublime Text 2, Mac –> TextMate 2 当然你也可以用 Vim 或 Sublime text 2;</p>
<p>2.安装 Ruby 和 Rails 开发环境可以按照这个流程：《如何快速正确的安装 Ruby, Rails》;</p>
<p>3.看完 <a href="http://guides.rubyonrails.org">http://guides.rubyonrails.org</a> 这里有 繁体版本；</p>
<p>4.通过学习 Rails Guides 实现一个博客系统，包涵完整的功能(包括 UI)，预计两周；</p>
<p>5.从头到尾一字不漏的看完 《应用 Rails 进行敏捷 Web 开发》；</p>
<p>6.回头审视之前的博客设计和《应用 Rails 进行敏捷 Web 开发》的区别，可以再重新搞个博客;</p>
<p>7.看完 《Getting Real》,预计两个小时；</p>
<p>8.搞明白 Gem, RVM, Bundler 是什么；</p>
<p>9.看完 《Rework》；</p>
<p>10.学习 Git, 上 <a href="http://github.com">http://github.com</a> 并长期使用；</p>
<p>11.看 <a href="http://railscasts.com">http://railscasts.com</a> 的视频教程，从 第一页 开始看，可以学到很多技巧，以免走弯路。</p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Windows下Python安装模块]]></title>
<link href="http://freealvin.github.io/blog/2013/08/27/windowsxia-pythonan-zhuang-mo-kuai/"/>
<updated>2013-08-27T17:39:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/08/27/windowsxia-pythonan-zhuang-mo-kuai</id>
<content type="html"><![CDATA[<!--more-->
<p>以安装Beautifulsoup4为例：</p>
<p>1.到网站上下载：<a href="http://www.crummy.com/software/BeautifulSoup/bs4/download/">http://www.crummy.com/software/BeautifulSoup/bs4/download/</a></p>
<p>2.解压文件到C:\Python27</p>
<p>3.cmd运行C:\Python27\BeautifulSoup>python setup.py install</p>
<p>4.注意库名：creating build\lib\bs4</p>
<p>5.测试一下是否能导入：</p>
<blockquote><blockquote><blockquote><p>import bs4</p></blockquote></blockquote></blockquote>
<p>如果不能导入，会提示：ImportError: No module named bs4</p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[重载运算符++]]></title>
<link href="http://freealvin.github.io/blog/2013/08/23/zhong-zai-yun-suan-fu-plus-plus/"/>
<updated>2013-08-23T13:19:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/08/23/zhong-zai-yun-suan-fu-plus-plus</id>
<content type="html"><![CDATA[<p>自定义重载运算符++时，为了区分前++和后++，在重载后++时添加哑参数。</p>
<!--more-->
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
<span class='line-number'>6</span>
<span class='line-number'>7</span>
</pre></td><td class='code'><pre><code class='c++'><span class='line'> <span class="n">F</span><span class="o">&</span> <span class="k">operator</span><span class="o">++</span><span class="p">(){</span>
</span><span class='line'> <span class="k">return</span> <span class="o">*</span><span class="k">this</span><span class="p">;</span>
</span><span class='line'> <span class="p">}</span>
</span><span class='line'> <span class="n">F</span> <span class="k">operator</span><span class="o">++</span><span class="p">(</span><span class="kt">int</span><span class="p">){</span><span class="c1">//此处使用到哑元</span>
</span><span class='line'> <span class="n">F</span> <span class="n">old</span><span class="p">(</span><span class="o">*</span><span class="k">this</span><span class="p">);</span>
</span><span class='line'> <span class="k">return</span> <span class="n">old</span><span class="p">;</span>
</span><span class='line'> <span class="p">}</span>
</span></code></pre></td></tr></table></div></figure>
<p>由上可知，自定义重载的++运算符，前++往往比后++效率高，所以一般选择使用前++</p>
]]></content>
</entry>
<entry>
<title type="html"><![CDATA[Python Dict]]></title>
<link href="http://freealvin.github.io/blog/2013/08/22/python-dict/"/>
<updated>2013-08-22T13:07:00+08:00</updated>
<id>http://freealvin.github.io/blog/2013/08/22/python-dict</id>
<content type="html"><![CDATA[<h1>dict</h1>
<p>字典的用法，dict的查找特别快捷。如果我们的项目经常用到搜索某些数据，最好用dict类型。</p>
<!--more-->
<h2>创建dict</h2>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
</pre></td><td class='code'><pre><code class='python'><span class='line'><span class="n">dict1</span> <span class="o">=</span> <span class="p">{}</span>
</span></code></pre></td></tr></table></div></figure>
<p>或者</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class='python'><span class='line'><span class="o">>>></span> <span class="nb">dict</span><span class="p">(</span><span class="n">sape</span><span class="o">=</span><span class="mi">4139</span><span class="p">,</span> <span class="n">guido</span><span class="o">=</span><span class="mi">4127</span><span class="p">,</span> <span class="n">jack</span><span class="o">=</span><span class="mi">4098</span><span class="p">)</span>
</span><span class='line'><span class="p">{</span><span class="s">'sape'</span><span class="p">:</span> <span class="mi">4139</span><span class="p">,</span> <span class="s">'jack'</span><span class="p">:</span> <span class="mi">4098</span><span class="p">,</span> <span class="s">'guido'</span><span class="p">:</span> <span class="mi">4127</span><span class="p">}</span>
</span></code></pre></td></tr></table></div></figure>
<p>或者用dict构造函数创建dict变量</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
</pre></td><td class='code'><pre><code class='python'><span class='line'><span class="n">dict2</span> <span class="o">=</span> <span class="nb">dict</span><span class="p">([(</span><span class="n">key1</span><span class="p">,</span> <span class="n">value1</span><span class="p">),(</span><span class="n">key2</span><span class="p">,</span><span class="n">value2</span><span class="p">),</span><span class="o">...</span><span class="p">]</span>
</span></code></pre></td></tr></table></div></figure>
<p>表达式创建</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class='python'><span class='line'><span class="o">>>></span> <span class="n">dict3</span> <span class="o">=</span> <span class="p">{</span><span class="n">x</span><span class="p">:</span> <span class="n">x</span><span class="o">**</span><span class="mi">2</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">6</span><span class="p">)}</span>
</span><span class='line'><span class="p">{</span><span class="mi">2</span><span class="p">:</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">4</span><span class="p">:</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">6</span><span class="p">:</span> <span class="mi">36</span><span class="p">}</span>
</span></code></pre></td></tr></table></div></figure>
<h2>添加元素</h2>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
<span class='line-number'>3</span>
<span class='line-number'>4</span>
<span class='line-number'>5</span>
</pre></td><td class='code'><pre><code class='python'><span class='line'><span class="n">tel</span> <span class="o">=</span> <span class="p">{}</span>
</span><span class='line'><span class="c">#dict1[key] = value</span>
</span><span class='line'><span class="n">tel</span><span class="p">[</span><span class="s">'guido'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">4127</span>
</span><span class='line'><span class="n">tel</span><span class="p">[</span><span class="s">'jack'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">4098</span>
</span><span class='line'><span class="n">tel</span><span class="p">[</span><span class="s">'sape'</span><span class="p">]</span> <span class="o">=</span> <span class="mi">4193</span>
</span></code></pre></td></tr></table></div></figure>
<h2>获取元素值</h2>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
</pre></td><td class='code'><pre><code class='python'><span class='line'><span class="n">num1</span> <span class="o">=</span> <span class="n">tel</span><span class="p">[</span><span class="s">'sape'</span><span class="p">]</span>
</span></code></pre></td></tr></table></div></figure>
<p>如果键不存在，tel[key]操作会出错，所以在获取元素之前，需要判断元素键是否存在
判断方法？</p>
<figure class='code'><div class="highlight"><table><tr><td class="gutter"><pre class="line-numbers"><span class='line-number'>1</span>
<span class='line-number'>2</span>
</pre></td><td class='code'><pre><code class='python'><span class='line'> <span class="k">if</span> <span class="n">tel</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">"snape"</span><span class="p">):</span>
</span><span class='line'> <span class="n">num1</span> <span class="o">=</span> <span class="n">tel</span><span class="p">[</span><span class="s">"snape"</span><span class="p">]</span>
</span></code></pre></td></tr></table></div></figure>
<p>或者</p>