How to get ip address associated with an interface

ro0tless · 02-04-2005, 07:55 AM

Title says it all.

/sbin/ifconfig does it, but I want to do it in a C (or any other compiler) programs, without /sbin/ifconfig. I just want to get IPv4 address from an interface name (eth0,eth1, etc.) in a program to inform my dns service automatically (I hope you know what I mean

)

TIA

ro0tless · 02-04-2005, 10:32 AM

Never mind. I got it.

ramnpathy76 · 02-07-2005, 12:34 AM

ro0tless, Could you update us with your findings...

Thanks

ro0tless · 02-07-2005, 02:59 AM

I found it in a source file of a client of another dns service (www.no-ip.com). It's not directly associated with network, but with the "interface" as a device.

see this code....

struct ifreq ifr;
........(omitted)
if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
.........(omitted)
strcpy(ifr.ifr_name, device);
if (ioctl(fd, SIOCGIFFLAGS, &ifr) < 0)

"struct ifreq" is defined in /usr/include/linux/if.h so it can hold ip address, netmask, etc, and interface name.

It's cool, isn't it?

But I myself haven't made my own yet

John Lumby · 10-03-2011, 12:18 PM

In case anyone else reads this, ro0tless's post has an incorrect ioctl parameter -

where he says
ioctl(fd, SIOCGIFFLAGS, &ifr)
it should read

ioctl(fd, SIOCGIFADDR, &ifr)