北华航天工业学院《编译原理》课程实验报告课程实验题目： 词法分析器实验 作者所在系部： 计算机科学与工程系 作者所在专业： 计算机科学与技术 作者所在班级： B08512 作 者 学 号： ___20084051212______ ____作 者 姓 名 ： 魏永丰 指导教师姓名： 李建义 完 成 时 间 ： 2011年3月25日 一、实验目的了解词法分析程序的两种设计方法：1.根据状态转换图直接编程的方式；2.利用DFA编写通用的词法分析程序二、实验内容及要求1．根据状态转换图直接编程编写一个词法分析程序，它从左到右逐个字符的对源程序进行扫描，产生一个个的单词的二元式，形成二元式（记号）流文件输出在此，词法分析程序作为单独的一遍，如下图所示具体任务有：（1）组织源程序的输入（2）拼出单词并查找其类别编号，形成二元式输出，得到单词流文件（3）删除注释、空格和无用符号（4）发现并定位词法错误，需要输出错误的位置在源程序中的第几行。
将错误信息输出到屏幕上5）对于普通标识符和常量，分别建立标识符表和常量表（使用线性表存储），当遇到一个标识符或常量时，查找标识符表或常量表，若存在，则返回位置，否则返回0并且填写符号表或常量表标识符表结构：变量名，类型（整型、实型、字符型），分配的数据区地址注：词法分析阶段只填写变量名，其它部分在语法分析、语义分析、代码生成等阶段逐步填入常量表结构：常量名，常量值三、实验程序设计说明1．实验方案设计 1．Initscanner函数：程序初始化：输入并打开源程序文件和目标程序文件，初始化保留字表 2．Scanner函数：若文件未结束，反复调用lexscan函数识别单词3．Lexscan函数：根据读入的单词的第一个字符确定调用不同的单词识别函数4．Isalpha函数：识别保留字和标识符5．Isnumber函数：识别整数，如有精力，可加入识别实数部分工功能6．Isanotation函数：处理除号/和注释7．Isother函数识别其他特殊字符8．Output函数：输出单词的二元式到目标文件，输出格式（单词助记符，单词内码值），如（int，-）（rlop，>）……9．Error函数：输出错误信息到屏幕10．除此之外，还可以设置查符号表，填写符号表等函数，学生可自行设计。
2．程序源代码#include#include#include#include#define MAX 10//保留字符号长度#define MAXSIZE 45//保留字和特殊符号表长度#define NUM 30//标识符和常数的个数FILE *in,*out;// 指向文件的指针char infile[MAX];//文件名字char token[MAX];char Word[NUM][MAX];//标识符char consts[NUM][MAX];//常数char lownum[NUM][MAX]={"0","1","2","3","4","5","6","7","8","9", "10","11","12","13","14","15","16","17","18","19" "20","21","22","23","24","25","26","27","28","29"}; //自定义表int n=1;//行号int num=0; //错误统计数typedef struct Key_word//保留字和特殊符号表结构{ //int keyNum; char keyWord[MAX]; char keySign[MAX]; char keyValue[MAX];}Key_word;//初始化保留字表Key_word Key[MAXSIZE]={{"int","int","-"},{"char","char","-"},{"float","float","-"}, {"void","void","-"},{"const","const","-"},{"for","for","-"}, {"if","if","-"},{"else","else","-"},{"then","then","-"}, {"while","while","-"},{"switch","switch","-"},{"break","break","-"}, {"begin","begin","-"},{"end","end","-"},{"","",""}, {"","",""},{"","id",""},{"","num",""}, {"+","+","-"},{"-","-","-"},{"*","*","-"}, {"/","/","-"},{"%","%","-"},{"(","(","-"}, {")",")","-"},{"[","[","-"},{"]","]","-"}, {"","",""},{"<","rlop","<"},{">","rlop",">"}, {"<=","rlop","<="},{">=","rlop",">="},{"=","rlop","="}, {"!=","rlop","!="},{";",";","-"},{"","",""}, {"/=","/=","-"},{"+=","+=","-"},{"-=","-=","-"}, {"*=","*=","-"},{"%=","%=","-"},{"||","or","-"}, {"&&","and","-"},{"!","not","-"},{"=","=","-"}};//打开关闭文件int Initscanner(){ printf("请输入要输入的文件:\n"); scanf("%s",infile); if((in=fopen(infile,"r"))==NULL) { printf("cannot open infile!\n"); return 0; } if((out=fopen("word.txt","a+"))==NULL) { printf("cannot open outfile!\n"); return 0; } return 0;}//写入文件void Output(int n,int m){ fputs("(",out); fputs(Key[n].keySign,out); fputs(",",out); if(m==-1) fputs(Key[n].keyValue,out); else fputs(lownum[m],out);//下标 fputs(")",out);}//Isalpha函数：识别保留字和标识符int Isalpha(){ int i; for(i=0;i<16;i++)//关键字 { if(strcmp(token,Key[i].keyWord)==0) { Output(i,-1); return 0; } } //标识符Word[NUM][MAX] for(i=0;i'||token[0]=='!'||token[0]=='%') { ch=getc(in); if(ch=='=') token[i++]=ch; else remove(); } else if(token[0]=='|') { ch=getc(in); if(ch=='|') token[i++]=ch; else remove(); } else if(token[0]=='&') { ch=getc(in); if(ch=='&') token[i++]=ch; else remove(); } token[i]='\0'; for(i=18;i<45;i++) { if(strcmp(token,Key[i].keyWord)==0) { Output(i,-1); break; } } if(i==45) { num++; printf("\n第(%d)行 : 字符错误 : %s字符非法\n",n,token); }}void Scanner(){ char ch; int i; ch=getc(in); while(!feof(in)) { while(ch==' '||ch=='\t'||ch=='\n') //先统计行数 { if(ch=='\n') ++n; ch=getc(in); } if(((ch>='a')&&(ch<='z'))||(ch=='_'))//标识符 isalpha(ch)单词 { i=1; token[0]=ch; ch=getc(in); while(((ch>='a')&&(ch<='z'))||((ch>='0')&&(ch<='9')))//word number { token[i++]=ch; ch=getc(in); } token[i]='\0'; Isalpha(); } else if((ch>='0')&&(ch<='9'))//整数 { i=1; token[0]=ch; ch=getc(in); while(isdigit(ch)) { token[i++]=ch; ch=getc(in); } token[i]='\0'; Isnumber(); } else if(ch=='/')//区分 "/" , "/=" , "/*" { token[0]=ch; Isanotation(); ch=getc(in); } else //特殊字符 { token[0]=ch; Isother(); ch=getc(in); } }}void show(){ int i; char ch; printf("\n二元式:\n"); rewind(out); while(!feof(out)) { printf("%c",getc(out)); } printf("\n标志符表\n"); for(i=0;i
在实验过程中，得到了同学的帮助才得以完成本实验基本达到了老师的要求，实现了词法分析的基本功能。