Here are 2 methods to get the ip address of a hostname :
The first method uses the traditional gethostbyname function to retrieve information about a hostname/domain name.
Code
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#include<stdio.h> //printf |
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#include<string.h> //memset |
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#include<stdlib.h> //for exit(0); |
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#include<sys/socket.h> |
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#include<errno.h> //For errno - the error number |
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#include<netdb.h> //hostent |
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#include<arpa/inet.h> |
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int hostname_to_ip(char * , char *); |
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int main(int argc , char *argv[]) |
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{ |
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if(argc <2) |
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{ |
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printf("Please provide a hostname to resolve"); |
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exit(1); |
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} |
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|
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char *hostname = argv[1]; |
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char ip[100]; |
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|
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hostname_to_ip(hostname , ip); |
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printf("%s resolved to %s" , hostname , ip); |
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|
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printf("\n"); |
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|
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} |
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/* |
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Get ip from domain name |
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*/ |
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int hostname_to_ip(char * hostname , char* ip) |
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{ |
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struct hostent *he; |
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struct in_addr **addr_list; |
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int i; |
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|
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if ( (he = gethostbyname( hostname ) ) == NULL) |
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{ |
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// get the host info |
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herror("gethostbyname"); |
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return 1; |
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} |
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addr_list = (struct in_addr **) he->h_addr_list; |
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|
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for(i = 0; addr_list[i] != NULL; i++) |
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{ |
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//Return the first one; |
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strcpy(ip , inet_ntoa(*addr_list[i]) ); |
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return 0; |
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} |
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|
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return 1; |
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} |
Compile and Run
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$ gcc hostname_to_ip.c && ./a.out www.google.com |
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www.google.com resolved to 74.125.235.16 |
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$ gcc hostname_to_ip.c && ./a.out www.msn.com |
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www.msn.com resolved to 207.46.140.34 |
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$ gcc hostname_to_ip.c && ./a.out www.yahoo.com |
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www.yahoo.com resolved to 98.137.149.56 |
The second method uses the getaddrinfo function to retrieve information about a hostname/domain name.
Code
1 |
#include<stdio.h> //printf |
2 |
#include<string.h> //memset |
3 |
#include<stdlib.h> //for exit(0); |
4 |
#include<sys/socket.h> |
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#include<errno.h> //For errno - the error number |
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#include<netdb.h> //hostent |
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#include<arpa/inet.h> |
8 |
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int hostname_to_ip(char * , char *); |
10 |
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int main(int argc , char *argv[]) |
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{ |
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if(argc <2) |
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{ |
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printf("Please provide a hostname to resolve"); |
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exit(1); |
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} |
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|
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char *hostname = argv[1]; |
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char ip[100]; |
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|
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hostname_to_ip(hostname , ip); |
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printf("%s resolved to %s" , hostname , ip); |
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|
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printf("\n"); |
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|
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} |
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/* |
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Get ip from domain name |
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*/ |
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int hostname_to_ip(char *hostname , char *ip) |
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{ |
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int sockfd; |
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struct addrinfo hints, *servinfo, *p; |
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struct sockaddr_in *h; |
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int rv; |
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memset(&hints, 0, sizeof hints); |
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hints.ai_family = AF_UNSPEC; // use AF_INET6 to force IPv6 |
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hints.ai_socktype = SOCK_STREAM; |
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if ( (rv = getaddrinfo( hostname , "http" , &hints , &servinfo)) != 0) |
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{ |
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fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv)); |
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return 1; |
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} |
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// loop through all the results and connect to the first we can |
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for(p = servinfo; p != NULL; p = p->ai_next) |
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{ |
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h = (struct sockaddr_in *) p->ai_addr; |
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strcpy(ip , inet_ntoa( h->sin_addr ) ); |
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} |
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|
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freeaddrinfo(servinfo); // all done with this structure |
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return 0; |
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} |
Compile and Run
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$ gcc hostname_to_ip.c && ./a.out www.google.com |
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www.google.com resolved to 74.125.235.19 |
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$ gcc hostname_to_ip.c && ./a.out www.yahoo.com |
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www.yahoo.com resolved to 72.30.2.43 |
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$ gcc hostname_to_ip.c && ./a.out www.msn.com |
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www.msn.com resolved to 207.46.140.34 |
