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

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.

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e.g.ptr = strtok(str, DELIM);

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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.











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// Program to check if a given string is valid IPv4 address or not 


#include <stdio.h> 


#include <stdlib.h> 


#include <string.h> 


  


#define DELIM "." 


  


/* function to check whether the string passed is valid or not */


bool valid_part(char* s) 


{ 


    int n = strlen(s); 


    // if length of passed string is more than 3 then it is not valid 


    if (n > 3) 


        return false; 


    // check if the string only contains digits 


    // if not then return false 


    for (int i = 0; i < n; i++) 


        if ((s[i] >= '0' && s[i] <= '9') == false) 


            return false; 


    string str(s); 


    // if the string is "00" or "001" or "05" etc then it is not valid 


    if (str.find('0') == 0 && n > 1) 


        return false; 


    stringstream geek(str); 


    int x; 


    geek >> x; 


    // the string is valid if the number generated is between 0 to 255 


    return (x >= 0 && x <= 255); 


} 


  


/* return 1 if IP string is valid, else return 0 */


int is_valid_ip(char* ip_str) 


{ 


    // if empty string then return false 


    if (ip == NULL) 


        return 0; 


    int i, num, dots = 0; 


    int len = strlen(ip); 


    int count = 0; 


    // the number dots in the original string should be 3 


    // for it to be valid 


    for (int i = 0; i < len; i++) 


        if (ip[i] == '.') 


            count++; 


    if (count != 3) 


        return false; 


    // See following link for strtok() 


    // http:// pubs.opengroup.org/onlinepubs/009695399/functions/strtok_r.html 


    char *ptr = strtok(ip_str, DELIM); 


    if (ptr == NULL) 


        return 0; 


  


    while (ptr) { 


  


        /* after parsing string, it must be valid */


        if (valid_part(ptr)) { 


            /* parse remaining string */


            ptr = strtok(NULL, "."); 


            if (ptr != NULL) 


                ++dots; 


        } 


        else


            return 0; 


    } 


  


    /* valid IP string must contain 3 dots */


    // this is for the cases such as 1...1 where originally the 


    // no. of dots is three but after iteration of the string we find it is not valid 


    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; 


} 



















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Output: 


Valid
Valid
Not valid
Not valid


This article is compiled by Narendra Kangralkar. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.


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