Programming-in-D-in-Chinese
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compiler.html

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<title>Compiler</title>
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编译器</h4>
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用 D 编程时经常会用到两个工具，它们分别是<i style="outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-repeat: initial initial;">文本编辑器</i>和<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">编译器</i>。D
程序正是在文本编辑器里写就。</p>
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当使用类似 D 语言的<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">编译型</i>语言时，需要理解编译的概念和编译器的功能。</p>
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机器码</h5>
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计算机的大脑是微处理器(或 CPU ，中央处理单元的简称)。告知 CPU 要做事叫做<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">编码</i>,而何时该做何事的指令则叫做<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">机器码</i>。</p>
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大多数 CPU
都使用特定架构的机器码，而这些机器码指令取决于底层架构设计阶段时的硬件约束。它们在最底层由电子信号实现。在这层，编码的舒适度不是主要考虑因素，所以直接按照
CPU 机器码形式编写程序非常困难。</p>
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机器码指令都是特定的数字，它们表示 CPU 支持的各种操作。例如，对于虚构的 8 位 CPU 来说，数字 4 可能表示载入操作，数字 5
可能表示存储操作，而数字 6 可能表示递增操作。假定最左边 3 位表示操作码，最右边 5 位表示用于运算的值，该 8 位 CPU 上机器码示例程序如下所示:</p>
<pre class="mono" style="margin: 0.5em 1em 0.75em 16px; padding: 0.5em; border: 1px dotted rgb(153, 204, 153); outline: 0px; font-size: 1em; vertical-align: baseline; background-color: rgb(255, 255, 255); color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-position: initial initial; background-repeat: initial initial;"><b style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 13px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">Operation   		Value           Meaning</b>
   100      	11110        	LOAD     	11110
   101      	10100        	STORE     	10100
   110      	10100        	INCREMENT   	10100
   000      	00000        	PAUSE
</pre>
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由于太贴近硬件，机器码不适合表示<i style="outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-repeat: initial initial;">扑克牌</i>或<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">学生记录</i>此类较高层次的概念。</p>
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编程语言</h5>
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编程语言的设计目标是用来对 CPU
高效编程，且有能力描述高级概念。编程语言不处理底层硬件约束，它们的主要目的是使用和表现上的简易舒适，更易于人类理解，有点类似于自然语言:</p>
<pre class="mono" style="margin: 0.5em 1em 0.75em 16px; padding: 0.5em; border: 1px dotted rgb(153, 204, 153); outline: 0px; font-size: 1em; vertical-align: baseline; background-color: rgb(255, 255, 255); color: rgb(0, 0, 0); font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-position: initial initial; background-repeat: initial initial;">if (a_card_has_been_played()) {
   display_the_card();
}
</pre>
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然而，编程语言依然比口语更严格、正规。</p>
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编译型语言</h5>
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一些编程语言编写的程序在成为可执行程序之前，必须先编译。这样的语言会生成更加快速的执行程序，但开发过程则分成了两个主要步骤:编写程序和编译程序。</p>
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通常，编译型语言会在程序运行之前有助于捕获编程错误。</p>
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D 就是一门编译型语言。</p>
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解释型语言</h5>
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一些编程语言不需要编译。这样的语言称之为<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">解释型语言</i>。程序编码完成即可直接运行。例如，Python,
Ruby, 和 Perl
等解释型语言。由于没有编译步骤，此类语言开发过程相对更简单。另一方面，解释型语言编写的程序在运行时由于每次都要先分析解释，所以相对于编译型语言编写的程序，运行速度要慢一些。</p>
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通常，解释型语言在编写时很多类型错误都发现不了，除非程序运行起来。</p>
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编译器</h5>
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编译器的目的就是翻译:把编程语言编写的程序翻译成机器码，即把程序员的语言翻译成 CPU 语言。这个翻译过程称为<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">编译</i>。每种编译器都会理解某种特定编程语言，这称为某种语言编译器。例如，“D
编译器”。</p>
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编译错误</h5>
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当编译器按照语言规则编译程序时，一旦碰到<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">非法</i>指令就会停止编译。非法指令指的是超出语言规范的地方。诸如圆括号未匹配，分号丢失，关键字拼错的问题都会引起编译错误。</p>
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当编译器看到某段可疑但又不是错误的代码时，会发送<i style="margin: 0px; padding: 0px; border: 0px; outline: 0px; font-size: 16px; vertical-align: baseline; background-color: transparent; background-position: initial initial; background-repeat: initial initial;">编译警告</i>。但是，警告几乎总是指示一个实际错误或错误风格，所以在实践中，应当把警告当作错误对待。</p>
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