Calling endhostent(), when such a call is not needed,
ends up closing fd 0 by accident.

main()
{
        endhostent();
}

Breakpoint 2, 0x281a8dc0 in close () from /lib/libc.so.7
(gdb) where
#0  0x281a8dc0 in close () from /lib/libc.so.7
#1  0x28152518 in __res_nclose () from /lib/libc.so.7
#2  0x2817c585 in __dns_getanswer () from /lib/libc.so.7
#3  0x080485b3 in main () at endhostent_bug.c:4

hopo $ truss ./a.out
...
close(0)                                         = 0 (0x0)
...
process exit, rval = 0

Except the usual runtime chores, close(0) is the only visible systemcall.