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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
Updated on: 30-Jul-2019
6K+ Views
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