How can we get the ip address like ifconfig using C program?

How can we get the ip address like ifconfig using C program?
The question is not the same as what I asked.
The Ip I got was not same as the ifconfig.
I beleive that using ifconfig can get the true ip address
and can ping the IP.
So gethostent(),gethostbyname(), maybe retrieve the ip
address from /etc/hosts,....
Can you help me to write a code like ifconfig
which is not use gethostent with reading /etc/hosts,
(Because /etc/hosts is wrong in my computer.)
 




Because I use rc.inet1 to set the IP of mycomputer,
These files /etc/hosts , /etc/hostname  was not corrected.
That is to say,for example ,
the ip /etc/hosts is 192.168.0.1,
but in the rc.inet1 192.168.0.3,
when using ifconfig , I find the eth0 is 192.168.0.3.
I used Slakware 7.0 distribution.