C Program to validate an IP address

In this program we will see how to validate an IP address using C. The IPv4 addresses are represented in dot-decimal notation. There are four decimal numbers (all are ranging from 0 to 255). These four numbers are separated by three dots.

An example of a valid IP is: 192.168.4.1

To validate the IP address we should follow these steps

• Tokenize the string (IP address) using the dot “.” delimiter

• If the sub strings are containing any non-numeric character, then return false

• If the number in each token is not in range 0 to 255, then return false

• If there are exactly three dots and four parts then it is a valid IP address

Example Code

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <ctype.h> int validate_number(char *str) {    while (*str) {       if(!isdigit(*str)){ //if the character is not a number, return          false          return 0;       }       str++; //point to next character    }    return 1; } int validate_ip(char *ip) { //check whether the IP is valid or not    int i, num, dots = 0;    char *ptr;    if (ip == NULL)       return 0;       ptr = strtok(ip, "."); //cut the string using dor delimiter       if (ptr == NULL)          return 0;    while (ptr) {       if (!validate_number(ptr)) //check whether the sub string is          holding only number or not          return 0;          num = atoi(ptr); //convert substring to number          if (num >= 0 && num <= 255) {             ptr = strtok(NULL, "."); //cut the next part of the string             if (ptr != NULL)                dots++; //increase the dot count          } else         return 0;     } if (dots != 3) //if the number of dots are not 3, return false return 0; return 1; } int main() { char ip1[] = "192.168.4.1"; char ip2[] = "172.16.253.1"; char ip3[] = "192.800.100.1"; char ip4[] = "125.512.100.abc"; validate_ip(ip1)? printf("Valid
"): printf("Not valid
"); validate_ip(ip2)? printf("Valid
"): printf("Not valid
"); validate_ip(ip3)? printf("Valid
"): printf("Not valid
"); validate_ip(ip4)? printf("Valid
"): printf("Not valid
"); }

Output

Valid Valid Not valid Not valid