how to get local ip adress

wwwnuwan · 03-25-2009, 10:50 PM

Hi,
How can I get local IP adress within a C program?

I tried this with gethostname function but it can not be helped since i dnt know the host name of the machine.

Thanks

vart · 03-25-2009, 10:57 PM

Quote:

Originally Posted by wwwnuwan

Hi,
How can I get local IP adress within a C program?

I tried this with gethostname function but it can not be helped since i dnt know the host name of the machine.

Thanks

read about gethostname

wwwnuwan · 03-25-2009, 11:07 PM

i tried with gethostname.
but it returns the hostname like "myLaptop".
I just need the ip like 192.168.10.10
my prev code was like as follows

Code:

    memset( hostname , 0 , MAXHOSTNAMELEN );
    gethostname( hostname,MAXHOSTNAMELEN );
    printf("MAXHOSTNAMELEN = %i \n " , MAXHOSTNAMELEN);

bithub · 03-25-2009, 11:38 PM

Passing your hostname to gethostbyname() should work. Depending on how your system is set up though, this may just return "127.0.0.1".

vart · 03-26-2009, 12:06 AM

Quote:

Originally Posted by bithub

Passing your hostname to gethostbyname() should work. Depending on how your system is set up though, this may just return "127.0.0.1".

you get a list of IPs - one of it could be 127.0.0.1, you should iterate through the list to find all local IPs

wwwnuwan · 03-26-2009, 01:01 AM

could you please give a some code example for this?

now my programe is as follows.

Code:

    char *hostname = malloc(MAXHOSTNAMELEN );
    memset( hostname , 0 , MAXHOSTNAMELEN );
    gethostname( hostname,MAXHOSTNAMELEN );
    struct hostent hostn = mallock(sizeof(struct hostent));
    gethostbyname(hostname);

here then how can i get the ip and print it onto the console?

vart · 03-26-2009, 01:11 AM

Quote:

Originally Posted by wwwnuwan

could you please give a some code example for this?

now my programe is as follows.

Code:

    char *hostname = malloc(MAXHOSTNAMELEN );
    memset( hostname , 0 , MAXHOSTNAMELEN );
    gethostname( hostname,MAXHOSTNAMELEN );
    struct hostent hostn = mallock(sizeof(struct hostent));
    gethostbyname(hostname);

here then how can i get the ip and print it onto the console?

There is a lot of samples in the net...

Winsock Programmer's FAQ: Get the Local IP Address(es) - for example

wwwnuwan · 03-26-2009, 05:07 AM

Hi,
Finaly i found the fellowing programs to obtain the local ip .
but it returns 127.0.1.1
please advice what goes wrong with this?

Code:

struct hostent *he;
struct in_addr a;

  int main (int argc)
{
    char *hostname = malloc(MAXHOSTNAMELEN );
    memset( hostname , 0 , MAXHOSTNAMELEN );
    gethostname( hostname,MAXHOSTNAMELEN );
    printf("hostname = %s \n " , hostname) ;
  he = gethostbyname (hostname);
  if (he)
  {
    printf("name: %s\n", he->h_name);
    while (*he->h_aliases)
      printf("alias: %s\n", *he->h_aliases++);
    while (*he->h_addr_list)
    {
      bcopy(*he->h_addr_list++, (char *) &a, sizeof(a));
      printf("address: %s\n", inet_ntoa(a));
    }
  }
  else
  printf("error \n");
    //herror(argv[0]);
  return 0;
}

Thanks.

wwwnuwan · 03-26-2009, 05:47 AM

I think this has no way to work out since my machine name (which I get by gethostname() method) is not in a DNS.
so I think it returns 127.0.0.1

any ideas about it?

Thanks.

wwwnuwan · 03-26-2009, 05:48 AM

sory its 127.0.1.1

bithub · 03-26-2009, 12:39 PM

Are you on windows or linux?

On linux, gethostbyname() will just return whatever is in /etc/hosts. You can always add a line to the hosts file which has your correct IP address.

Another option is to run "ipconfig" or "ifconfig" (depending on your OS), and parse out the result.

brewbuck · 03-26-2009, 12:51 PM

What you want is the address of the actual interface. You can't really get at this information in a portable way.

gethostbyname() is portable, but if it returns multiple answers you have no way of knowing which one is correct.

Honestly, I'd bite the bullet and use a non-portable method to query the network interface and obtain its address directly.

slingerland3g · 03-31-2009, 08:07 AM

Going with bithub's suggestion will be your best bet, especially if you have many interfaces, say a dual homed server with tied up vlans to them.

03-25-2009, 10:50 PM	#1
wwwnuwan Registered User Join Date: Mar 2009 Posts: 22	how to get local ip adress Hi, How can I get local IP adress within a C program? I tried this with gethostname function but it can not be helped since i dnt know the host name of the machine. Thanks
wwwnuwan is offline

03-25-2009, 11:07 PM	#3
wwwnuwan Registered User Join Date: Mar 2009 Posts: 22	i tried with gethostname. but it returns the hostname like "myLaptop". I just need the ip like 192.168.10.10 my prev code was like as follows Code: memset( hostname , 0 , MAXHOSTNAMELEN ); gethostname( hostname,MAXHOSTNAMELEN ); printf("MAXHOSTNAMELEN = %i \n " , MAXHOSTNAMELEN);
wwwnuwan is offline

03-25-2009, 11:38 PM	#4
bithub Registered User Join Date: Sep 2004 Location: California Posts: 3,020	Passing your hostname to gethostbyname() should work. Depending on how your system is set up though, this may just return "127.0.0.1".
bithub is offline

03-26-2009, 01:01 AM	#6
wwwnuwan Registered User Join Date: Mar 2009 Posts: 22	could you please give a some code example for this? now my programe is as follows. Code: char *hostname = malloc(MAXHOSTNAMELEN ); memset( hostname , 0 , MAXHOSTNAMELEN ); gethostname( hostname,MAXHOSTNAMELEN ); struct hostent hostn = mallock(sizeof(struct hostent)); gethostbyname(hostname); here then how can i get the ip and print it onto the console?
wwwnuwan is offline

03-26-2009, 05:47 AM	#9
wwwnuwan Registered User Join Date: Mar 2009 Posts: 22	I think this has no way to work out since my machine name (which I get by gethostname() method) is not in a DNS. so I think it returns 127.0.0.1 any ideas about it? Thanks.
wwwnuwan is offline

03-26-2009, 05:48 AM	#10
wwwnuwan Registered User Join Date: Mar 2009 Posts: 22	sory its 127.0.1.1
wwwnuwan is offline

03-26-2009, 12:39 PM	#11
bithub Registered User Join Date: Sep 2004 Location: California Posts: 3,020	Are you on windows or linux? On linux, gethostbyname() will just return whatever is in /etc/hosts. You can always add a line to the hosts file which has your correct IP address. Another option is to run "ipconfig" or "ifconfig" (depending on your OS), and parse out the result.
bithub is offline

03-26-2009, 12:51 PM	#12
brewbuck Senior software engineer Join Date: Mar 2007 Location: Portland, OR Posts: 5,768	What you want is the address of the actual interface. You can't really get at this information in a portable way. gethostbyname() is portable, but if it returns multiple answers you have no way of knowing which one is correct. Honestly, I'd bite the bullet and use a non-portable method to query the network interface and obtain its address directly. __________________ "Congratulations on your purchase. To begin using your quantum computer, set the power switch to both off and on simultaneously." -- raftpeople@slashdot
brewbuck is offline

03-31-2009, 08:07 AM	#13
slingerland3g Registered User Join Date: Jan 2008 Location: Seattle Posts: 575	Going with bithub's suggestion will be your best bet, especially if you have many interfaces, say a dual homed server with tied up vlans to them.
slingerland3g is offline

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