# Program to validate an IP address

Write a program to Validate an IPv4 Address.

According to Wikipedia, IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1

## Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

Following are steps to check whether a given string is valid IPv4 address or not:

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.

```// 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 */
int is_valid_ip(char *ip_str)
{
int i, num, dots = 0;
char *ptr;

if (ip_str == NULL)
return 0;

// See following link for strtok()
// http://pubs.opengroup.org/onlinepubs/009695399/functions/strtok_r.html
ptr = strtok(ip_str, DELIM);

if (ptr == NULL)
return 0;

while (ptr) {

/* after parsing string, it must contain only digits */
if (!valid_digit(ptr))
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
return 0;
}

/* valid IP string must contain 3 dots */
if (dots != 3)
return 0;
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_ip(ip1)? printf("Valid\n"): printf("Not valid\n");
is_valid_ip(ip2)? printf("Valid\n"): printf("Not valid\n");
is_valid_ip(ip3)? printf("Valid\n"): printf("Not valid\n");
is_valid_ip(ip4)? printf("Valid\n"): printf("Not valid\n");
return 0;
}
```

Output:

```Valid
Valid
Not valid
Not valid```

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