Get ip address from hostname in C using Linux sockets-白红宇的个人博客

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                    
       
                  9           int hostname_to_ip(char *  , char *);          
       
                  10                    
       
                  11           int 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                    
       
                  32           int 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         
       
                  2          www.google.com resolved to 74.125.235.16         
       
                  3                    
       
                  4          $ gcc hostname_to_ip.c && ./a.out www.msn.com         
       
                  5          www.msn.com resolved to 207.46.140.34         
       
                  6                    
       
                  7          $ gcc hostname_to_ip.c && ./a.out www.yahoo.com         
       
                  8          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>         
       
                  5          #include<errno.h> //For errno - the error number         
       
                  6          #include<netdb.h> //hostent         
       
                  7          #include<arpa/inet.h>         
       
                  8                    
       
                  9           int hostname_to_ip(char *  , char *);          
       
                  10                    
       
                  11           int 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                    
       
                  32           int 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         
       
                  2          www.google.com resolved to 74.125.235.19         
       
                  3                    
       
                  4          $ gcc hostname_to_ip.c && ./a.out www.yahoo.com         
       
                  5          www.yahoo.com resolved to 72.30.2.43         
       
                  6                    
       
                  7          $ gcc hostname_to_ip.c && ./a.out www.msn.com         
       
                  8          www.msn.com resolved to 207.46.140.34

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