IP address/地址 檢查

一、Determine if a string is a valid IP address in C

Beej's Guide to Network Programming
二、9.14. inet_ntop(), inet_pton()

三、Program to validate an IP address

step 1) Parse string with 「.」 as delimiter using 「strtok()」 function.
e.g. ptr = strtok(str, DELIM);

step 2)
……..a) If ptr contains any character which is not digit then return 0
……..b) Convert 「ptr」 to decimal number say ‘NUM’
……..c) If NUM is not in range of 0-255 return 0
……..d) If NUM is in range of 0-255 and ptr is non-NULL increment 「dot_counter」 by 1
……..e) if ptr is NULL goto step 3 else goto step 1

step 3) if dot_counter != 3 return 0 else return 1.

方法Ⅰ

// Program to check if a given string is valid IPv4 address or not
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#define DELIM "."
 
/* return 1 if string contain only digits, else return 0 */
int valid_digit(char *ip_str)
{
    while (*ip_str) {
        if (*ip_str >= '0' && *ip_str <= '9')
            ++ip_str;
        else
            return 0;
    }
    return 1;
}
 
/* return 1 if IP string is valid, else return 0 */
/* Check whether ip_address conforms to xxx.xxx.xxx.xxx, and there are 3 dots/'.'  */
/* 暫時只能檢查符合常規IP地址的字符串，好比192.168.3.100， 若是是 八、192.167.8等這種很是規的，則處理不了。 */
int is_valid_IPV4(char * ip_str)
{
    int i, num, dots = 0;
    char *ptr;

    if(ip_str == NULL)
        return 0;

    // 15+1 can't be replace by sizeof(ip_str), as the sizeof(*ip_str) is 4.
    char *tmpstr = (char *)malloc(15+1);
    memset(tmpstr, 0, sizeof(tmpstr));
    memcpy(tmpstr, ip_str, 15);
    printf("tmpstr is %s\n", tmpstr);

    // See following link for strtok()
    // http://pubs.opengroup.org/onlinepubs/009695399/functions/strtok_r.html
    //ptr = strtok(ip_str, DELIM);
    ptr = strtok(tmpstr, DELIM);
 
    if (ptr == NULL){
        free(tmpstr);
        return 0;
    }
 
    while (ptr) {
 
        /* after parsing string, it must contain only digits */
        if (!valid_digit(ptr)){
            free(tmpstr);
            return 0;
        }
 
        num = atoi(ptr);
 
        /* check for valid IP */
        if (num >= 0 && num <= 255) {
            /* parse remaining string */
            ptr = strtok(NULL, DELIM);
            if (ptr != NULL)
                ++dots;
        } else{
            free(tmpstr);
            return 0;
        }
    }
 
    /* valid IP string must contain 3 dots */
    if (dots != 3){
        free(tmpstr);
        return 0;
    }


    free(tmpstr);
    return 1;
}
 
// Driver program to test above functions
int main()
{
    char ip1[] = "128.0.0.1";
    char ip2[] = "125.16.100.1";
    char ip3[] = "125.512.100.1";
    char ip4[] = "125.512.100.abc";
    is_valid_IPV4(ip1)? printf("Valid\n"): printf("Not valid\n");
    is_valid_IPV4(ip2)? printf("Valid\n"): printf("Not valid\n");
    is_valid_IPV4(ip3)? printf("Valid\n"): printf("Not valid\n");
    is_valid_IPV4(ip4)? printf("Valid\n"): printf("Not valid\n");
    
    printf("ip4 is %s\n", ip4);
    return 0;
}

結果是：

Valid
Valid
Not Valid
Not Valid

方法Ⅱ

#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int isValidIpAddress(char *ipAddress)
{
    struct sockaddr_in sa;
    /* 函數 inet_pton會同時將 ipAddress複製到 函數的第3個參數上區，格式爲 struct sock_addr_in* */
    int result = inet_pton(AF_INET, ipAddress, &(sa.sin_addr));
    
    return result != 0;
}

void main()
{
    char ip1[]="192.168.3.1";
    char ip2[]="192.168.3.a";
    char ip3[]="192.168.3";
    isValidIpAddress(ip1) ? printf("Valid\n"): printf("Not valid\n");
    isValidIpAddress(ip2) ? printf("Valid\n"): printf("Not valid\n");
    isValidIpAddress(ip3) ? printf("Valid\n"): printf("Not valid\n");

    return;
}

結果是：

Valid
Not Valid
Not Valid