200602281700255.html

软件工程的红包书

<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 每一种程序设计语言可以被看作是一套包含语法、词汇和含义的正式规范。</P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 这些规范通常包括：</P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 数据和数据结构 <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 指令及流程控制 <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 引用机制和重用 <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 设计哲学 <BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 大多数被广泛使用或经久不衰的语言，拥有负责标准化的组织，经常会晤来创造及发布该语言的正式定义，并讨论扩展或贯彻现有的定义。</P>
<P><STRONG>数据和数据结构</STRONG></P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 现代计算机内部的数据都只以二元方式储存，即开-关<a href="200603061709535.html" tppabs="http://www.itisedu.com/phrase/200603061709535.html" target="_new">模式</a>(on-off)。现实世界中代表信息的各种数据，例如名字、银行账号、<a href="200604231331545.html" tppabs="http://www.itisedu.com/phrase/200604231331545.html" target="_new">度量</a>以及同样低端的二<a href="javascript:if(confirm('http://www.itisedu.com/phrase/200603141328355.html  \n\nThis file was not retrieved by Teleport Pro, because it was unavailable, or its retrieval was aborted, or the project was stopped too soon.  \n\nDo you want to open it from the server?'))window.location='http://www.itisedu.com/phrase/200603141328355.html'" tppabs="http://www.itisedu.com/phrase/200603141328355.html" target="_new">元数据</a>，都经由程序设计语言整理，成为高端的概念。</P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 一个程序中专门处理数据的那个系统被称为程序语言的型态系统(<a href="javascript:if(confirm('http://www.itisedu.com/phrase/200604231258125.html  \n\nThis file was not retrieved by Teleport Pro, because it was unavailable, or its retrieval was aborted, or the project was stopped too soon.  \n\nDo you want to open it from the server?'))window.location='http://www.itisedu.com/phrase/200604231258125.html'" tppabs="http://www.itisedu.com/phrase/200604231258125.html" target="_new">type</a> system)；对型态系统的研究和设计被称为型态理论(type theory)。语言可以被分为静态型态系统(statically typed systems)，例如C++和Java，和动态型态系统(dynamically typed systems)，例如Lisp，JavaScript，Tcl和Prolog。前者可被进一步分为包含宣告型态(manifest type)的语言，即每一个变量和函数的型态都清楚地宣告，或type-inferred语言（例如MUMPS，ML）。</P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 大多数语言还能够在内置的型态基础上组合出复杂的数据结构型态（使用数组，列表，堆栈，文件等等）。<a href="javascript:if(confirm('http://www.itisedu.com/phrase/200603010948085.html  \n\nThis file was not retrieved by Teleport Pro, because it was unavailable, or its retrieval was aborted, or the project was stopped too soon.  \n\nDo you want to open it from the server?'))window.location='http://www.itisedu.com/phrase/200603010948085.html'" tppabs="http://www.itisedu.com/phrase/200603010948085.html" target="_new">面向对象语言</a>（<a href="javascript:if(confirm('http://www.itisedu.com/phrase/200604231401015.html  \n\nThis file was not retrieved by Teleport Pro, because it was unavailable, or its retrieval was aborted, or the project was stopped too soon.  \n\nDo you want to open it from the server?'))window.location='http://www.itisedu.com/phrase/200604231401015.html'" tppabs="http://www.itisedu.com/phrase/200604231401015.html" target="_new">Object Oriented</a> Language，又译作“物件导向语言”）允许程序员定义新的数据型态，即“<a href="200603090845215.html" tppabs="http://www.itisedu.com/phrase/200603090845215.html" target="_new">对象</a>”或“物件”（objects），以及运行于该对象的函数（functions）和方法（methods）。</P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 除了何时以及如何确定表达式和型态的联系，另外一个重要的问题就是语言到底定义了哪些型态，以及允许哪些型态作为表达式的值。诸如C编程语言之类的低端语言允许程序命名内存位置、内存区域以及编译时的常量；ANSI C甚至允许表达式返回结构值（struct values）。功能性的语言一般允许变量直接使用运行时计算出的值，而不是指出该值可能储存的内存地址。</P>
<P><STRONG>指令及流程控制</STRONG></P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 一旦数据被确定，机器必须被告知如何对这些数据进行处理。较简单的指令可以使用关键字或定义好的语法结构来完成。不同的语言利用序列系统来取得或组合这些语句。除此之外，一个语言中的其他指令也可以用来控制处理的过程（例如分支、循环等）。</P>
<P><STRONG>引用机制和重用</STRONG></P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 引用的中心思想是必须有一种间接设计储存空间的方法。最常见的方法是通过命名变量。根据不同的语言，进一步的引用可以包括指向其他储存空间的指针。还有一种类似的方法就是命名一组指令。大多数程序设计语言使用宏调用、过程调用或函数调用。使用这些代替的名字能让程序更灵活，并更具重用性。</P>
<P><STRONG>程序设计语言的历史</STRONG></P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 二十世纪四十年代当计算机刚刚问世的时候，程序员必须手动控制计算机。当时的计算机十分昂贵，唯一想到利用程序设计语言来解决问题的人是德国工程师楚泽（Konrad Zuse）。</P>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 几十年后，计算机的价格大幅度下跌，而计算机程序也越来越复杂。也就是说，开发时间已经远比运行时间来得宝贵。</P>
<P>于是，新的集成、可视的开发环境越来越流行。它们减少了所付出的时间、金钱（以及脑细胞）。只要轻敲几个键，一整段代码就可以使用了。这也得益于可以重用的程序代码库。</P>
<P><STRONG>常见的程序设计语言</STRONG></P>
<P>ActionScript <BR>APL、A＋和J <BR>Ada <BR>汇编语言 <BR><a href="javascript:if(confirm('http://www.itisedu.com/phrase/200603021801255.html  \n\nThis file was not retrieved by Teleport Pro, because it was unavailable, or its retrieval was aborted, or the project was stopped too soon.  \n\nDo you want to open it from the server?'))window.location='http://www.itisedu.com/phrase/200603021801255.html'" tppabs="http://www.itisedu.com/phrase/200603021801255.html" target="_new">AWK</a> <BR>Basic、Fortran <BR>VBScript <BR>Brainfuck <BR>C、C++ <BR>C＃ <BR>Clipper <BR>COBOL <BR>dBase <BR>PASCAL、<a href="javascript:if(confirm('http://www.itisedu.com/phrase/200604042241255.html  \n\nThis file was not retrieved by Teleport Pro, because it was unavailable, or its retrieval was aborted, or the project was stopped too soon.  \n\nDo you want to open it from the server?'))window.location='http://www.itisedu.com/phrase/200604042241255.html'" tppabs="http://www.itisedu.com/phrase/200604042241255.html" target="_new">Delphi</a> <BR>Forth <BR>FoxPro <BR>F＃ <BR>Fava <BR>IDL <BR>Java <BR>JavaScript <BR>J# <BR>LISP <BR>Lua <BR>LOGO <BR>Modula <BR>Perl <BR>PHP <BR>PL/I <BR>Prolog <BR>Python <BR>Ruby <BR>Scheme <BR>Smalltalk <BR><a href="javascript:if(confirm('http://www.itisedu.com/phrase/200604022014515.html  \n\nThis file was not retrieved by Teleport Pro, because it was unavailable, or its retrieval was aborted, or the project was stopped too soon.  \n\nDo you want to open it from the server?'))window.location='http://www.itisedu.com/phrase/200604022014515.html'" tppabs="http://www.itisedu.com/phrase/200604022014515.html" target="_new">SQL</a> <BR>Tcl/Tk <BR>Visual Basic <BR>Visual FoxPro <BR><a href="200604231236585.html" tppabs="http://www.itisedu.com/phrase/200604231236585.html" target="_new">XML</a> <BR></FONT></P></div>
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