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

Beej's Guide to Network Programming

2、9.14. inet_ntop(), inet_pton()

3、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,比如192.168.3.100, 如果是 8、192.167.8等這種非常規的,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

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