词法分析之浮点数分析

来源：互联网发布：js控制span显示隐藏编辑：程序博客网时间：2024/06/06 23:19

#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;
}