[FFmpeg-devel] [PATCH][RFC] -std=c99

Luca Abeni lucabe72
Thu Aug 21 12:04:29 CEST 2008

Hi all,

Luca Abeni wrote:
>>  Does anyone know a standardised way of doing whatever this code does?
> I cannot speak about standards, but it seems to me that this is the same 
> code used by all the other programs that need to join multicast groups 
> and/or to receive/send multicast traffic.
> I cannot reproduce the build failure here, but maybe the problem can be 
> fixed by defining _BSD_SOURCE at the top of the file?

Ok, I studied the problem a little bit more, and:
1) IPv4 multicast does not seem to be standardised in POSIX, single unix
    specification, & friends (only IPv6 multicast seems to be standard!)
2) however, IPv4 multicast is supported by BSD systems
3) in a recent "namespace cleanup" glibc removed some of the definitions
    needed for IPv4 multicast, unless the user is asking for GNU extensions,
    BSD compatibility, or System V
    However, this removal has been done in a funny way: the ip_mreq structure
    is not defined, but IP_ADD_MEMBERSHIP is still defined. I call this
    "funny" because setsockopt(IP_ADD_MEMBERSHIP) always wants a parameter
    of type ip_mreq, so I think it does not make any sense to define
    IP_ADD_MEMBERSHIP if ip_mreq is not provided (BTW, this is the reason
    why the compilation is failing).
    The first libc affected by this funny behaviour should be 2.8.
4) I believe that adding "#define _BSD_SOURCE" at the top of udp.c (before
    all the "#include"s) should fix the compilation (can anyone test? I do
    not see the compilation failure, so I cannot test). And asking fro BSD
    compatibility when using sockets looks like a good idea, so I think
    this could be an acceptable solution...



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