UDP - recvfrom() call

There are two simple programs: A, and B communicating through UDP (socket() called with SOCK_DGRAM). A just bounces all datagrams.
B sends a datagram to A, calls recvfrom and then
examines the sockaddr *from field.

Depedning on:
a) sockaddr_in declaration or allocation
b) recvfrom calling point
c) B's compilation host
I'm getting different results:

Compiled on my machine (RH 6.1):

sockaddr_in  | recvfrom()     | result
-----------------------------
main()          | main()           | A's address
answer0()     | answer0()      | EINVAL
B.c              | answer1()      | 0.0.0.0
malloc()        | answer2()     | EINVAL

Compiled on my university host:

sockaddr_in  | recvfrom()     | result
--------------------------
main()          | main()           | A's address
answer0()     | answer0()      | 0.0.0.0
B.c              | answer1()      | 0.0.0.0
malloc()        | answer2()     | 0.0.0.0

I don't like the idea of putting all my code
in main(), so hope there's someone who has
at least the slightest idea about what's going
on and how to make it work. I'll provide any
additional information, if it is necessary.

Sources of A and B are here: http://rainbow.mimuw.edu.pl/~robson/AB.tgz 
LVL 4
RobsonAsked:
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munsieConnect With a Mentor Commented:
in your get_answer2() routine, you didn't set the length field to be the sizeof(answer).  Actually, you didn't do this in multiple places...

set length before calling recvfrom() will fix your problem.

good luck,
dennis
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munsieCommented:
the code would be very helpful, if you don't mind... i have a few ideas, but I would like to see what A and B are doing.

thanks,
dennis
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RobsonAuthor Commented:
I've put sources of A and B at http://rainbow.mimuw.edu.pl/~robson/AB.tgz
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RobsonAuthor Commented:
Edited text of question.
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RobsonAuthor Commented:
Thank's a lot, dennis!
This requirement isn't mentioned either in man page, nor in Steven's book (I 've nearly broken its cover in anger). Also in example programs given by my network-programming teacher (he's going to score some, too) initialization isn't made.

Last, but not least:
I MISSED GREAT SCI-FI CONVENTION BECAUSE OF THIS EFFING BUG!
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munsieCommented:
glad it helped... sorry about the sci-fi convention, though

dennis
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RobsonAuthor Commented:
NOTE: I was wrong about Stevens' "Un*x Network Programming" - it explains this problem. I promise to read it carefully and with respect - and no more violence, of course :-).  
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