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<p class="MsoNormal">Hi, <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I think the getlogin function works without a full function declaration since it is a system call that is run by the shell as a privileged call. The manual for getlogin specifies:
<o:p></o:p></p>
<p class="MsoNormal" style="text-indent:.5in">“The name is normally associated with a login shell at the time a session is created, and is inherited by all processes descended from the login shell.”<o:p></o:p></p>
<p class="MsoNormal" style="text-indent:.5in"><o:p> </o:p></p>
<p class="MsoNormal">This leads me to believe that the underlying implementation of getlogin is written in the OS itself and C code will only have to declare the function either through unistd.h or writing “char * getlogin(void);”.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I could be wrong, looking forward to hearing what other people think!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best Regards, <o:p></o:p></p>
<p class="MsoNormal">Tim<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">cs631apue-bounces@lists.stevens.edu <cs631apue-bounces@lists.stevens.edu> on behalf of Jan Schaumann <jschauma@stevens.edu><br>
<b>Date: </b>Wednesday, September 8, 2021 at 12:46 PM<br>
<b>To: </b>cs631apue@lists.stevens.edu <cs631apue@lists.stevens.edu><br>
<b>Subject: </b>[cs631apue] function forward declarations<o:p></o:p></span></p>
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<p class="MsoNormal">Hello,<br>
<br>
In the Week 01 checkpoint, one of you asked:<br>
<br>
---<br>
Why does the program of welcome.c work after we<br>
declare the getlogin function in the front without<br>
providing an 'include' for the header file of unistd.h<br>
as told in the manual page?<br>
<br>
It should not work without implementation of getlogin<br>
function! <br>
---<br>
<br>
Can one of you help answer this question?<br>
<br>
-Jan<br>
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