This program will read an IP address in String and check whether it is a valid IPv4 address or not. IPv4 is an IP format of xxx.xxx.xxx.xxx and each octet has value between 0 to 255.
/*C program to check given string is a valid IPv4 address or not.*/ #include <stdio.h> #include <string.h> #include <stdlib.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; 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[] = "128.0.0.251"; char ip2[] = "128.16.100.1"; char ip3[] = "128.512.100.1"; char ip4[] = "125.512.200.cde"; 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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Checking String is Valid IPv4 address or not
Output:
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