Finding subnet mask on Linux in C

Question

I am interested in finding the subnet mask of the local host programatically in Linux preferably through the native C api.

Answer 1

getifaddrs() will give you a list of your network interfaces and the field ifa_netmask should be the mask for each.

Answer 2

The ifconfig utility uses ioctl() with the SIOCGIFNETMASK command to get the netmask. But I think Duck's answer is more user-friendly.