学院(系)名称:计算机工程系姓名学号专业班级实验项目实验一:词法分析课程名称编译原理课程代码 03102432013年 4月28 日第 1、2 节实验时间实验地点第一教学楼1508 2013年5月 7 日第1 、2 节批改意见成绩教师签字: 实验内容:实现标准C语言词法分析器实验目的:1(掌握程序设计语言词法分析的设计方法;2(掌握DFA的设计与使用方法;3(掌握正规式到有限自动机的构造方法;实验要求:1(单词种别编码要求基本字、运算符、界符:一符一种;标识符:统一为一种;常量:按类型编码;2(词法分析工作过程中建立符号表、常量表，并以文本文件形式输出;3(词法分析的最后结果以文本文件形式输出;4(完成对所设计词法分析器的功能测试，并给出测试数据和实验结果;5(为增加程序可读性，请在程序中进行适当注释说明;6(整理上机步骤，总结经验和体会;7(认真完成并按时提交实验报告。
实验步骤:1.基本思想:从源程序中依次读入字符并解析,与关键字、运算符、结束符进行比较，得出其中的关键字，并将它存入到数组中去。
2.程序源代码:#include<stdio.h>#include<cstring>#include<stdlib.h>#define MaxSize1 17//关键字的个数#define MaxSize2 20//运算符的个数#define MaxSize3 4//结束符的个数//数据结构struct TNode{char value[20]; //存放标识符的值int number; //存放标识符的种别码char description[20];//描述}KeyWords[MaxSize1],Operation[MaxSize2],EndOperation[MaxSize3];//存放关键字的数组char*WordsBuff[MaxSize1]={"const","long","float","double","void","main", "if","else","then","break","int","char","include","for","while","printf","scanf"};//存放运算符的数组char*OperationBuff[MaxSize2]={"+","-","*","/","+=","-=","*=","++","--","<","<=",">",">=","<>","=","(",")","#","{","}"}; char EndOperationBuff[MaxSize3]={' ',';','\n','\t'};//存放词法分析程序输出的结果TNode Table1[500];TNode Variable[100];//标识符表TNode Const[100];//关键字数组初始化void inputKeyWords(char * buff[],int size) {//关键字编码从1-sizefor(int i=0;i<size;i++){strcpy(KeyWords[i].value,buff[i]);KeyWords[i].number=i+1;strcpy(KeyWords[i].description,"关键字");}}//运算符数组初始化void inputOperation(char * buff[],int size){//运算符编码从50-(50+size)for(int i=0;i<size;i++){strcpy(Operation[i].value,buff[i]);Operation[i].number=i+50;strcpy(Operation[i].description,"运算符");}}//结束符数组初始化void inputEndOperation(char buff[],int size) {//结束符编码从100-(100+size);for(int i=0;i<size;i++){EndOperation[i].value[0]=buff[i]; EndOperation[i].value[1]='\0';EndOperation[i].number=i+100;strcpy(EndOperation[i].description,"结束符"); }}//输出数据结构数组中的信息void outputInfo(TNode a[],int size){for(int i=0;i<size;i++){printf("(%d",a[i].number);printf("\t");printf("%s)",a[i].value);printf("\t");printf(a[i].description);printf("\n");}}void outInfoToFile(TNode a[],int size,FILE *out) {//将词法分析程序的结果输出到文件中去for(int i=0;i<size;i++){fprintf(out,"(%d",a[i].number);fprintf(out,"\t");fprintf(out,"%s)",a[i].value);fprintf(out,"\t");fprintf(out,a[i].description);fprintf(out,"\n");}}//从文件中读取一个字符//返回文件中读取的字符char getChar(FILE *fp){char ch=fgetc(fp);return ch;}//判读是否是运算符int isOperation(char a[]) {//返回i表示是运算符在运算符数组中的位置//返回-1表示不是运算符int result;for(int i=0;i<MaxSize2;i++){result=strcmp(a,Operation[i].value); 第4页共12页if(result==0){return i;break;}}return -1;}//判读是否是关键字int isKeyWords(char a[]){//返回i表示在关键字表中的位置//返回-1表示不是关键字int result;for(int i=0;i<MaxSize1;i++){result=strcmp(a,KeyWords[i].value); if(result==0){return i;break;}}return -1;}//判读是否是结束符int isEndOperation(char a){//返回i表示是结束符在结束符表中的位置//返回-1表示不是结束符for(int i=0;i<MaxSize3;i++){if(a==EndOperation[i].value[0]){return i;break;}}return -1;}//判读是否是字符int isChar(char a) { //返回1表示是字符//返回0表示不是字符第5页共12页if(a>='a'&&a<='z') return 1;else if(a>'A'&&a<='Z') return 1;elsereturn 0;}//判读是否是数字int isDigit(char a) {//返回1表示是数字//返回0表示不是数字if(a>='0'&&a<='9') return 1;elsereturn 0;}int count=0;//记录结果表中的关键字及运算符等表项个数，用于返回 int count1=0;//记录标识符的表项个数int count2=0;//记录常量的表项的个数//从屏幕上面获得字符并解析,返回在结果表中的表项 int start1(FILE *in) {char buff[20];//用于保存单词的缓冲区char nextchar[2];char temp[20];//用于保存变量或常量的类型数组int i=0;//缓冲区指针int a;//比较的结果指针char op[3];//用于保存第一个运算符op[2]='\0';nextchar[0]=fgetc(in);nextchar[1]='\0';while(nextchar[0]!=EOF){if(isChar(nextchar[0])){buff[i]=nextchar[0];i++;nextchar[0]=fgetc(in);}else if(isDigit(nextchar[0])){buff[i]=nextchar[0];i++;nextchar[0]=fgetc(in);}else if(nextchar[0]=='\r'||nextchar[0]=='\n')第6页共12页{buff[i]='\0';a=isKeyWords(buff);if(a!=-1&&i>0){strcpy(Table1[count].value,KeyWords[a].value);Table1[count].number=KeyWords[a].number;strcpy(Table1[count].description,KeyWords[a].description); count++;//计数器加一i=0;//清空缓冲区}else if(i>0){if(isChar(buff[0])){//是标识符strcpy(Variable[count1].value,buff);Variable[count1].number=count1;strcpy(Variable[count1].description,"标识符");count1++;//计数器加一i=0;//清空缓冲区}else if(isDigit(buff[0])){//是常量strcpy(Const[count2].value,buff);Const[count2].number=count2;strcpy(Const[count2].description,"常量"); count2++;//计数器加一i=0;//清空缓冲区}}else{//缓冲区为空～}//处理回车符与换行符nextchar[0]=fgetc(in);}else if(isEndOperation(nextchar[0])!=-1) {buff[i]='\0';a=isKeyWords(buff);if(a!=-1&&i>0)第7页共12页{strcpy(Table1[count].value,KeyWords[a].value);Table1[count].number=KeyWords[a].number;strcpy(Table1[count].description,KeyWords[a].description); strcpy(temp,KeyWords[a].value);count++;//计数器加一i=0;//清空缓冲区}else if(i>0){if(isChar(buff[0])){//是标识符strcpy(Variable[count1].value,buff);Variable[count1].number=count1;strcpy(Variable[count1].description,"标识符");count1++;//计数器加一i=0;//清空缓冲区}else if(isDigit(buff[0])){//是常量strcpy(Const[count2].value,buff);Const[count2].number=count2;strcpy(Const[count2].description,"常量");count2++;//计数器加一i=0;//清空缓冲区}}else{//缓冲区为空～}nextchar[0]=fgetc(in);}else if((a=isOperation(nextchar))!=-1){//首先输出缓冲区中的数据buff[i]='\0';a=isKeyWords(buff);if(a!=-1&&i>0){strcpy(Table1[count].value,KeyWords[a].value);Table1[count].number=KeyWords[a].number;strcpy(Table1[count].description,KeyWords[a].description); 第8页共12页count++;//计数器加一i=0;//清空缓冲区}else if(i>0){if(isChar(buff[0])){//是标识符strcpy(Variable[count1].value,buff);Variable[count1].number=count1;strcpy(Variable[count1].description,"标识符"); count1++;//计数器加一i=0;//清空缓冲区}else if(isDigit(buff[0])){//是常量strcpy(Const[count2].value,buff);Const[count2].number=count2;strcpy(Const[count2].description,"常量"); count2++;//计数器加一i=0;//清空缓冲区}}else{//缓冲区为空～}//处理运算符op[0]=nextchar[0];nextchar[0]=fgetc(in);if(nextchar[0]!='@'){if(isOperation(nextchar)!=-1){op[1]=nextchar[0];if((a=isOperation(op))!=-1){//输出双目运算符strcpy(Table1[count].value,Operation[a].value);Table1[count].number=Operation[a].number;strcpy(Table1[count].description,Operation[a].description); count++;//计数器加一//读取下一个字符nextchar[0]=fgetc(in);第9页共12页}else{//错误的双目运算符strcpy(Table1[count].value,op);Table1[count].number=-1;strcpy(Table1[count].description,"未定义的运算符");count++;//计数器加一//读取下一个字符nextchar[0]=fgetc(in);}}else{//输出一元运算符op[1]='\0';a=isOperation(op);strcpy(Table1[count].value,Operation[a].value);Table1[count].number=Operation[a].number;strcpy(Table1[count].description,Operation[a].description); count++;//计数器加一}}}}return count;}void main(){inputKeyWords(WordsBuff,MaxSize1); inputOperation(OperationBuff,MaxSize2); inputEndOperation(EndOperationBuff,MaxSize3); FILE *in,*out;bool Flag=true;while(Flag){printf("源文件的位置:C:\\input.txt\n");if((in=fopen("C:\\input.txt","r"))==NULL) {printf("读取源文件失败～\n");exit(0);}if((out=fopen("C:\\out.txt","w"))==NULL){printf("打开文件失败～\n");第10页共12页exit(0);}int MaxSize=start1(in);printf("关键字及运算符\n");fprintf(out,"关键字及运算符\n"); outputInfo(Table1,MaxSize); outInfoToFile(Table1,MaxSize,out); printf("标识符表:\n");fprintf(out,"标识符表:\n"); outputInfo(Variable,count1); outInfoToFile(Variable,count1,out); printf("常量表:\n");fprintf(out,"常量表:\n"); outputInfo(Const,count2); outInfoToFile(Const,count2,out); Flag=false;fclose(in);fclose(out);}}3.测试用例:int a=3;double b=4;int c;if(a>b)c=a;elsec=b;4.测试结果:第11页共12页5.心得体会:通过这次实验，我对编译原理这门专业必修课有了进一步的深层次了解，把理论知识应用于实验中，实验过程中对于转义字符，结束符、欠缺了考虑，在多次的调试和改进中最终完善了程序，而在调试过程中学习的知识得到了完善和补充，对词法分析器的理解更进一步。
