实验1-3 《编译原理》S语言词法分析程序设计方案一、实验目的了解词法分析程序的两种设计方法之一:根据状态转换图直接编程的方式;二、实验内容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、实验要求1.能对任何S语言源程序进行分析在运行词法分析程序时,应该用问答形式输入要被分析的S源语言程序的文件名,然后对该程序完成词法分析任务。
2.能检查并处理某些词法分析错误词法分析程序能给出的错误信息包括:总的出错个数,每个错误所在的行号,错误的编号及错误信息。
本实验要求处理以下两种错误(编号分别为1,2):1:非法字符:单词表中不存在的字符处理为非法字符,处理方式是删除该字符,给出错误信息,“某某字符非法”。
2:源程序文件结束而注释未结束。
注释格式为:/* …… */四、保留字和特殊符号表单词的构词规则:字母=[A-Za-z]数字=[0-9]标识符=(字母|_)(字母|数字)*数字=数字(数字)*(.数字+| )四、S语言表达式和语句说明1.算术表达式:+、-、*、/、%2.关系运算符:>、>=、<、<=、==、!=3.赋值运算符:=,+=、-=、*=、/=、%=4.变量说明:类型标识符变量名表;5.类型标识符:int char float6.If语句:if 表达式then 语句[else 语句]7.For语句:for(表达式1;表达式2;表达式3)语句8.While语句:while 表达式do 语句9.S语言程序:由函数构成,函数不能嵌套定义。
函数格式为:返回值函数名(参数){数据说明语句}五、程序参考结构说明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。
实验中,可以将某些类型的单词识别过程利用DFA算法实现,DFA算法参考如下:DFA(S=S0,MOVE[][],F[],ALPHABET[],ALLS[])/*S为状态,初值为DFA的初态,MOVE[][]为状态转换矩阵,F[] 为终态集,ALPHABET[] 为字母表,其中的字母顺序与MOVE[][] 中列标题的字母顺序一致。
ALLS[]为状态集*/ {Char Wordbuffer[10]=“”//单词缓冲区置空Nextchar=getchar();//读字符i=0;while(nextchar!=NULL)//NULL代表此类单词{ if (nextcha r!∈ALPHABET[]){ERROR(“非法字符”),return(“非法字符”);}S=MOVE[S][nextchar] //下一状态if(S=NULL)return(“不接受”);//下一状态为空,不能识别,单词错误wordbuffer[i]=nextchar ;//保存单词符号i++;nextchar=getchar();}Wordbuffer[i]=‘\0’;If(S∈F)return(wordbuffer);//接受Else return(“不接受”);}六、实验过程说明1.每人单独完成。
2.完成后,由老师验收,并给出成绩。
3.实验完成后,写出实验报告(要求交打印稿)。
报告内容要求如下:七、测试源程序示例://aa.cvoid aa( ){float rate,circle;rate=3;circle=3.14*rate*rate;}输出结果:(1)输出结果文件:(void,-)(id, 0) ((,-) (),-) ({,- ) ( float,-) (id,1)……(2)标识符的符号表:12345(3123实验地点:教10五楼计算机学院软一机房实验时间:第4周周二3单元、周四1单元、第五周周二3单元八、实验代码#include<stdio.h>#include<stdlib.h>#include<ctype.h>#include<string.h>#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);elsefputs(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<NUM;i++){if((Word[i][0]!=NULL)&&strcmp(token,Word[i])==0){Output(16,i);return 0;}if(Word[i][0]==NULL){strcpy(Word[i],token);Output(16,i);return 0;}}return 0;}int Isnumber()//Isnumber函数:consts[NUM][MAX]{int i;for(i=0;i<NUM;i++){if((consts[i][0]!=NULL)&&strcmp(token,consts[i])==0){Output(17,i);return 0;}if(consts[i][0]==NULL){strcpy(consts[i],token);Output(17,i);return 0;}}return 0;}void remove() //扫描指针回退一个字符{fseek(in,-1,SEEK_CUR);}//Isanotation函数:处理除号/和注释void Isanotation() //提示第一个字符已经存为/了{char ch,pre;ch=getc(in);if(ch=='=')// "/="Output(36,-1);else if(ch=='*')// "/*"{ch=getc(in);do{if(feof(in)){num++;printf("\n第(%d)行: 注释错误: /*后面的字符全部当做注释,缺少结束注释*/\n",n);break;}pre=ch;ch=getc(in);}while(pre!='*'||ch!='/');}else// "/"{remove(); //指针回退一个字符Output(21,-1);}}//Isother函数识别其他特殊字符void Isother(){ int i=1;int j=0;if(token[0]=='<'||token[0]=='>'||token[0]=='!'||token[0]=='%'){ch=getc(in);if(ch=='=')token[i++]=ch;elseremove();}else if(token[0]=='|'){ch=getc(in);if(ch=='|')token[i++]=ch;elseremove();}else if(token[0]=='&'){ch=getc(in);if(ch=='&')token[i++]=ch;elseremove();}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;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<NUM;i++){if(Word[i][0]!=NULL)printf("%d,%s\n",i,Word[i]);}printf("\n常数表\n");for(i=0;i<NUM;i++){if(consts[i][0]!=NULL)printf("%d,%s\n",i,consts[i]);}}void main(){Initscanner();Scanner();printf("\n共有%d个错误\n",num);show();fclose(in);fclose(out);}九、实验结果输入文件void aa( ) begin float rate,circle; rate=3;circle=3.14*rate;/******/ end 输出文件(void,-)(id,0)((,-)(),-)(begin,-)(float,-)(id,1)(id,2)(;,-)(id,1)(rlop,=)(num,0)(;,-)(id,2)(rlop,=)(num,0)(num,1)(*,-)(id,1)(;,-)(end,-)十、实验总结经过此次实验,了解了程序的词法构词规则和词法分析过程。