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1、词法分析器实验报告院系：专业：小组成员：学号：日期：一、实验的目的与任务词法分析的目的是将输入的源程序进行划分，给出基本符号（token）的序列，并掠过注解和空格等分隔符号。基本符号是与输入的语言定义的词法所规定的终结符。本实验要求学生编制一个读单词过程，从输入的源程序中，识别出各个具有独立意义的单词，即基本保留字、标识符、常数、运算符、分隔符五大类。并依次输出各个单词的内部编码及单词符号自身值。（遇到错误时可显示“Error”，然后跳过错误部分继续进行）。二、实验所要识别的单词分类1．关键字。*key[53]={"auto","bool","break",
2、"case","catch","char","class","const","continue","default","delete","do","double","else","enum","extern","false","float","for","friend","goto","if","inline","int","long","namespace","new","operator","private","protected","public","register","return","short","signed","sizeof","stati
3、c","struct","switch","template","this","throw","true","try","typedef","typename","union","unsigned","using","virtual","void","volatile","while"};2．标识符。符合文法标识符，由字符和数字组成，首字符必须为下划线或字母。（hjw,wyp2319,_zhg…..）3.数字。整型，浮点型，科学计数。4.运算符。*arithmetic[6]={"+","-","*","/","++","--"};5.关系运算符。*relat
4、ion[7]={"<","<=","=",">",">=","==","!="};6.分界符。*border[7]={",",";","{","}","(",")","//"};三、输出格式1)若为关键字，则输出格式为；例：关键字float,输出为2)若为一般标识符，则输出格式为；例：标识符fzu，输出为3)若为数字，则输出格式为；例：数字2325，输出为<2325,数字>4)若为算术运算符，则输出格式为<符号,算术运算符>；例：+,输出为<+,算术运算符>5)若
5、为关系运算符，则输出格式为<符号,关系运算符>；例：!=,输出为6)若出错，则输出格式为；例：错误输入为26.，则输出为<26.,ERROR>四、正则表达式：标识符id->letter_(letter_
6、digit)*无符号数number->digitoptitionalfractionoptionalexponent空白符ws->(blank
7、tab
8、newline)+关系运算符relop-><
9、>
10、<=
11、>=
12、=
13、!=运算符operator->+
14、-
15、*
16、/
17、++
18、--五、DFA状态转换图start<0ot
19、her=678return(relop,LE)54>=123other>=**return(relop,NE)return(relop,LT)return(relop,EQ)return(relop,GE)return(relop,GT)startletter9other1110letter/dig*1912141316151817startotherdigit.digitE+
20、-digitdigitdigitdigitEdigit*start+25+other*-262728293332other3031-**/六、流程图七、实验结果实验环境：Micros
21、oftWindows7下的MicrosoftVisualStudio2010输入输出输入输出输入输出八、结果分析用格式为.txt的文件输入，一个个字符去识别，根据DFA的状态图实现跳转，把未进入接受状态的单元存放进一个数组，到达接受状态，将识别出来的词和属性一起输出。其中识别得到的id与keyword转换过程相同，故最后得到的结果还要再判断是标识符还是关键字。由于关键词有限，可以建个表存放关键字，通过查表实现判断关键字。运算符和分隔符是有限的，所以把它们罗列去判断，只要是符合条件就接收。九、实验总结实验是理论的实践，但是通过实验加深了我们对理论课知识的理解和
22、运用，词法分析器更是如此。对输入的程序进行分析，将关
