[cs631apue] function forward declarations

[Jan Schaumann]

Hello,

In the Week 01 checkpoint, one of you asked:

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Why does the program of welcome.c work after we
declare the getlogin function in the front without
providing an 'include' for the header file of unistd.h
as told in the manual page?

It should not work without implementation of getlogin
function! 
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Can one of you help answer this question?

-Jan