C 判斷IP地址的合法性

#include <stdio.h>

int is_valid_ip(const char *ip) 
{ 
    int section = 0;  //每一節的十進制值 
    int dot = 0;       //幾個點分隔符 
    int last = -1;     //每一節中上一個字符 
    while(*ip)
    { 
        if(*ip == '.')
        { 
            dot++; 
            if(dot > 3)
            { 
                return 0; 
            } 
            if(section >= 0 && section <=255)
            { 
                section = 0; 
            }else{ 
                return 0; 
            } 
        }else if(*ip >= '0' && *ip <= '9')
        { 
            section = section * 10 + *ip - '0'; 
            if(last == '0')
            { 
                return 0; 
            } 
        }else{ 
            return 0; 
        } 
        last = *ip; 
        ip++;        
    }

    if(section >= 0 && section <=255)
    { 
        if(3 == dot)
        {
        section = 0; 
        printf ("IP address success!\n");       
        //printf ("%d\n",dot);
        return 0;
      }
    } 
    return 1; 
}

int main()
{
    is_valid_ip("192.249.23.123");
}