converting host to ip by sockaddr_in gethostname etc

Question

i need help converting hostname to ip and inserting to sockaddr_in->sin_addr to be able assign to char. For example i input: localhost and it gives me 127.0.0.1

I found code, but i dont know why it gives me wrong numbers

//---
#include <sys/types.h>
#include <netinet/in.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <time.h>
#include <sys/fcntl.h>
#include <netdb.h>
//---

///CZY WPISANO HOST

        struct in_addr inaddr;
        inaddr.s_addr = inet_addr(argv[1]);
        if( inaddr.s_addr == INADDR_NONE) //if sHost is name and not IP
        {
            struct hostent* phostent = gethostbyname( argv[1]);
            if( phostent == 0)
                bail("gethostbyname()");

            if( sizeof(inaddr) != phostent->h_length)
                bail("problem z inaddr"); // error something wrong,

            puts(argv[1]);
            inaddr.s_addr = *((unsigned long*) phostent->h_addr);

            //strdup( inet_ntoa(inaddr));
            srvr_addr = inet_ntoa(adr_srvr.sin_addr);
            puts(srvr_addr);
        }

I also wrote own code but i dont know how transfer from sockaddr to sockaddr_in data:

///CZY WPISANO HOST
    if(argv[1][0]>=(char)'a' && argv[1][0]<=(char)'Z')
    {
        struct hostent *hent;
        hent = gethostbyname(argv[1]);
        adr_srvr.sin_addr =  (struct in_addr*)hent->h_addr_list;

    }

adr_srvr is a char* type

I really need help, thanks!

Solution 1

Try something like this:

  struct hostent        *he;
  struct sockaddr_in  server;
  int                 socket;

  const char hostname[] = "localhost";

  /* resolve hostname */
  if ( (he = gethostbyname(hostname) ) == NULL ) {
      exit(1); /* error */
  }

  /* copy the network address to sockaddr_in structure */
  memcpy(&server.sin_addr, he->h_addr_list[0], he->h_length);
  server.sin_family = AF_INET;
  server.sin_port = htons(1337);

  /* and now  you can connect */
  if ( connect(socket, (struct sockaddr *)&server, sizeof(server) ) {
      exit(1); /* error */
  }

I wrote this code straight from my memory so I cannot guarantee that it works but I am pretty sure it should be OK.

Solution 2

This shell script compiles correct C code, which I believe will do what you want it to:

rm -f 1; cat > 1.c <<EOD; gcc -Wall -Werror 1.c -o 1; ./1

#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>

void
do_one(char *the_name,int port_number)
{
  int                  my_socket;

  char               **pointer_pointer;

  char                 answer[INET_ADDRSTRLEN];

  struct hostent      *returned_host;

  struct sockaddr_in   outgoing_address;

  printf("==========\n");

  printf("destination         : %s:%d\n",the_name,port_number);

  returned_host=gethostbyname(the_name);

  if(returned_host==NULL)
  {
    fprintf(stderr,"error %d\n",h_errno);

    return;
  }

  printf("host's official name: %s\n",returned_host->h_name);

  for(pointer_pointer=returned_host->h_aliases;
      *pointer_pointer;
      pointer_pointer++
     )
  {
    printf("alias               : %s\n",*pointer_pointer);
  }

  for(pointer_pointer=returned_host->h_addr_list;
      *pointer_pointer;
      pointer_pointer++
     )
  {
    inet_ntop(AF_INET,(void *)*pointer_pointer,answer,sizeof(answer));

    printf("IP address          : %s\n",answer);

    my_socket=socket(AF_INET,SOCK_STREAM,0);

    if(my_socket<0)
    {
      perror("socket()");

      return;
    }

    memset(&outgoing_address,0,sizeof(outgoing_address));
    outgoing_address.sin_family=AF_INET;
    outgoing_address.sin_port=htons(port_number);

    memmove(&outgoing_address.sin_addr,
            *pointer_pointer,
            sizeof(&outgoing_address.sin_addr)
           );

    if(connect(my_socket,(struct sockaddr*)&outgoing_address,sizeof(outgoing_address)))
    {
      perror("connect()");

      return ;
    }

    printf("connection established on file descriptor %d\n",my_socket);
  }

} /* do_one() */

int
main(void)
{
  do_one("localhost",80);
  do_one("localhost",81);
  do_one("127.0.0.1",80);
  do_one("tiger",80);
  do_one("www.google.com",80);

  return 0;

} /* main() */

EOD

The output I got was this:

==========
destination         : localhost:80
host's official name: localhost
IP address          : 127.0.0.1
connection established on file descriptor 3
==========
destination         : localhost:81
host's official name: localhost
IP address          : 127.0.0.1
connect(): Connection refused
==========
destination         : 127.0.0.1:80
host's official name: 127.0.0.1
IP address          : 127.0.0.1
connection established on file descriptor 5
==========
destination         : tiger:80
host's official name: tiger.x441afea5.org
alias               : tiger
IP address          : 10.0.0.1
connection established on file descriptor 6
==========
destination         : www.google.com:80
host's official name: www.l.google.com
alias               : www.google.com
IP address          : 74.125.229.50
connection established on file descriptor 7
IP address          : 74.125.229.52
connection established on file descriptor 8
IP address          : 74.125.229.48
connection established on file descriptor 9
IP address          : 74.125.229.49
connection established on file descriptor 10
IP address          : 74.125.229.51
connection established on file descriptor 11

Hope this helps.

Comments

[Bill Evans at Mariposa]

That's actually pretty good, coming straight from memory. I couldn't do it from memory like that. One must remember the socket() call, and also to zero out the sockaddr_in struct before filling it, because there are fields which you don't want accidentally set nonzero.

[R.. GitHub STOP HELPING ICE]

gethostbyname is deprecated and will be extremely problematic with the imminent transition to ipv6. Always use the modern getaddrinfo interface instead.

[Athabaska Dick]

Yeah thats true. I second that.

[Bill Evans at Mariposa]

I actually third that. W. Richard Stevens of happy memory says the same thing,but my answer (below) was intended not to give a turnkey solution, but to suggest an answer to "I don't know why it gives me wrong numbers".