When do you #include <stdlib.h>?

[Rodrigo Murillo]

I realized today that you can call functions that are in stdlib.h
without actually including them in your file.  But on the otherhand
you can include them.  Is there a hard fast rule?  Let me give an
example:

     printf("foo: %dl",atol(argv[1]));

The prototype for atol() resides in stdlib.h.  The above code compiles
without an #include <stdlib.h>, but the expresion yields rubbish.  When
the stdlib.h is included, it works fine.  What gives?  Why doesn't the 
compiler barf when it encounters atol() when the stdlib.h is NOT included?

-- 
_______________________________________________________________________________
 Rodrigo Murillo, University of Colorado - Boulder  (303) 761-0410 
 murillo at boulder.colorado.edu | ..{hao|nbires}!boulder!murillo
 ( Machines have less problems.  I'd like to be a machine. -- Andy Worhol )