How linux displays the network interfaces

[maheshgupta024]

Hi, I have question in the ifconfig command,
1. When I do an ifconfig command I see the some interfaces, but when i give ifconfig -a command I see complete list of interfaces. How linux knows what interfaces is inactive and which is active device. Is have did some googling and got to know that /sys/class/net/lo/operstate is the file. Is my understanding true or linux does some other stuff to find that..

2. Also how ifconfig gets the full details.

Because I have write a method in our project to get the complete list of interfaces and their respective details like ip, gatway, route, arp table etc.. I dont want to shell command in the c program to get the dtails becoz i have to do a grep and hell of stuff is required.. I want to use thing like ioctl to get the details
Can anyone help me in that..

Thanks in advance..