cifabianyi.cpp

词法分析,给定状态转换图,写出对应的词法分析程序

#include <stdio.h>
#include <ctype.h>
#include <string.h>

char *nexttoken();
char nextchar();
void next();
void back();
char *gettoken();

char cbuf[]="12.3*********klj12.2e2jj778";
int forward=-1;
int main(){
    while(1){
        printf("%s\n",nexttoken());
        if (forward >=strlen(cbuf)-1){
            getchar();
            return 0;
          }
    }
 }
 int state;
 int start;
 
 char *nexttoken(){
    char c;
    state =12;
    while(1){
        switch(state){
            case 12:
                c=nextchar();
                start=forward;
                if(isdigit(c)){
                    state=13;
                }else {
                    next();
                 }
                 break;
             case 13:
                c=nextchar();
                if(isdigit(c))
                    state=13;
                else if(c=='e'||c=='E')
                    state=16;
                else if(c=='.')
                    state=14;
                else
                    state=19;
                break;
             case 14:
                c=nextchar();
                if(isdigit(c))
                    state=15;
                break;
             case 15:
                c=nextchar();
                if(isdigit(c))
                    state=15;
                else if(c=='e'||c=='E')
                    state=16;
                else
                    state=19;
                break;
             case 16:
                c=nextchar();
                if(isdigit(c))
                    state=18;
                else if(c=='+'||c=='-')
                    state=17;
                break;
             case 17:
                c=nextchar();
                if(isdigit(c))
                    state=18;
                break;
             case 18:
                c=nextchar();
                if(isdigit(c))
                    state=18;
                else
                    state=19;
                break;
             case 19:
                back();
                return gettoken();
                }
        }
    }

            char nextchar(){
            forward++;
            return cbuf[forward];
             }
         
            void back(){
                forward--;
             }
             
             void next(){
                forward++;
              }
              
              char token_buf[128];
              char *gettoken(){
                int i,j=0;
                for(i=start;i<=forward;i++){
                    token_buf[j++]=cbuf[i];
                }
                token_buf[j]='\0';
                return token_buf;
               }