Get ip address from hostname in C using Linux sockets

最新推荐文章于 2024-05-24 17:15:20 发布

weixin_34007906

最新推荐文章于 2024-05-24 17:15:20 发布

阅读量95

点赞数

本文介绍两种方法来获取主机名对应的IP地址：一种是使用传统的gethostbyname函数，另一种是使用getaddrinfo函数。这两种方法均通过C语言实现，并提供了完整的代码示例及运行结果。

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

 
    1#include<stdio.h> //printf

    2#include<string.h> //memset

    3#include<stdlib.h> //for exit(0);

    4#include<sys/socket.h>

    5#include<errno.h> //For errno - the error number

    6#include<netdb.h> //hostent

    7#include<arpa/inet.h>

    8 

    9int hostname_to_ip(char *  , char *);

    10 

    11int main(int argc , char *argv[])

    12{

    13    if(argc <2)

    14    {

    15        printf("Please provide a hostname to resolve");

    16        exit(1);

    17    }

    18     

    19    char *hostname = argv[1];

    20    char ip[100];

    21     

    22    hostname_to_ip(hostname , ip);

    23    printf("%s resolved to %s" , hostname , ip);

    24     

    25    printf("\n");

    26     

    27}

    28/*

    29    Get ip from domain name

    30 */

    31 

    32int hostname_to_ip(char * hostname , char* ip)

    33{

    34    struct hostent *he;

    35    struct in_addr **addr_list;

    36    int i;

    37         

    38    if ( (he = gethostbyname( hostname ) ) == NULL)

    39    {

    40        // get the host info

    41        herror("gethostbyname");

    42        return 1;

    43    }

    44 

    45    addr_list = (struct in_addr **) he->h_addr_list;

    46     

    47    for(i = 0; addr_list[i] != NULL; i++)

    48    {

    49        //Return the first one;

    50        strcpy(ip , inet_ntoa(*addr_list[i]) );

    51        return 0;

    52    }

    53     

    54    return 1;

    55}

Compile and Run

 
    1$ gcc hostname_to_ip.c && ./a.out www.google.com

    2www.google.com resolved to 74.125.235.16

    3 

    4$ gcc hostname_to_ip.c && ./a.out www.msn.com

    5www.msn.com resolved to 207.46.140.34

    6 

    7$ gcc hostname_to_ip.c && ./a.out www.yahoo.com

    8www.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>

    5#include<errno.h> //For errno - the error number

    6#include<netdb.h> //hostent

    7#include<arpa/inet.h>

    8 

    9int hostname_to_ip(char *  , char *);

    10 

    11int main(int argc , char *argv[])

    12{

    13    if(argc <2)

    14    {

    15        printf("Please provide a hostname to resolve");

    16        exit(1);

    17    }

    18     

    19    char *hostname = argv[1];

    20    char ip[100];

    21     

    22    hostname_to_ip(hostname , ip);

    23    printf("%s resolved to %s" , hostname , ip);

    24     

    25    printf("\n");

    26     

    27}

    28/*

    29    Get ip from domain name

    30 */

    31 

    32int hostname_to_ip(char *hostname , char *ip)

    33{

    34    int sockfd; 

    35    struct addrinfo hints, *servinfo, *p;

    36    struct sockaddr_in *h;

    37    int rv;

    38 

    39    memset(&hints, 0, sizeof hints);

    40    hints.ai_family = AF_UNSPEC; // use AF_INET6 to force IPv6

    41    hints.ai_socktype = SOCK_STREAM;

    42 

    43    if ( (rv = getaddrinfo( hostname , "http" , &hints , &servinfo)) != 0)

    44    {

    45        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));

    46        return 1;

    47    }

    48 

    49    // loop through all the results and connect to the first we can

    50    for(p = servinfo; p != NULL; p = p->ai_next)

    51    {

    52        h = (struct sockaddr_in *) p->ai_addr;

    53        strcpy(ip , inet_ntoa( h->sin_addr ) );

    54    }

    55     

    56    freeaddrinfo(servinfo); // all done with this structure

    57    return 0;

    58}

Compile and Run

 
    1$ gcc hostname_to_ip.c && ./a.out www.google.com

    2www.google.com resolved to 74.125.235.19

    3 

    4$ gcc hostname_to_ip.c && ./a.out www.yahoo.com

    5www.yahoo.com resolved to 72.30.2.43

    6 

    7$ gcc hostname_to_ip.c && ./a.out www.msn.com

    8www.msn.com resolved to 207.46.140.34