gethostbyname() only returns the address of local host on linux

I'm trying to portably (Windows & Linux) find all of the IP addresses of the local machine. The method I am using is to first call gethostname(), and then pass the result of that to gethostbyname(), whic开发者_Python百科h returns an array of ip addresses.

The problem is that on linux, the only address I get back is 127.0.0.1. This works on Windows, and I've seen a few people state that this will not work on Linux if your network was configured by DHCP (don't know if that's a true statement).

Is this not the correct way to do this on Linux?

It is not the correct way on unix/linux. The correct way involves ioctls to pull the necessary information.

struct ifreq ifc_buffer[MAX_NUM_IFREQ];
ioctl(s, SIOCGIFCONF, &ifc)  # Interface list
num_ifreq = ifc.ifc_len / sizeof(struct ifreq);
for(cnt=0;cnt<num_ifreq;cnt++)
  struct ifreq *ifr = &ifc.ifc_req[cnt]
  ioctl(s, SIOCGIFADDR, ifr); # get ip address

There are also more modern methods involving:

if_nameindex()

Doing a SO search for if_nameindex and SIOCGIFCONF will yield a number of questions similar to this one.

This happens because on most distributions you have this in /etc/hosts:

127.0.0.1       localhost.localdomain   localhost aiur

gethostbyname simply resolves the hostname (aiure in this example) to an address. If it finds it in /etc/hosts it's more than happy to give you that.

Back to the question. Unfortunately I don't believe you can get all the addresses of your machine in a portable way. You can do it in a Unix-portable way, like ifconfig does. Open a socket s and do an ioctl(..., SIOCGIFCONF, ...).

By the way, gethostbyname is obsolete if you believe kernel.org and deprecated if you believe MSDN.