What's un.h? (About network programming...)

[Shridhar Daithankar <shridhar_daithankar@xxxxxxxxxx>]

Hi all

 I was fiddling a bit with socket programming, having stevens handy. I tried 
unix domain sockets. But the examples didn't worked.

 gcc gave an error for 'struct sockaddr_un'  that unknown size etc. 

I did a grep -r on /usr/include(My fevourite ...:-)) fro 'struct sockaddr_un' 
and included <sys/un.h> and it worked...

 Any idea why so? I though whatever files listed by man of every system call 
in program should suffice.... What does this file do?

 Shridhar