Thread: understanding macro __SOCKADDR_COMMON (sa_);

  1. #1
    Registered User
    Join Date
    Jan 2009

    understanding macro __SOCKADDR_COMMON (sa_);

    Hi all:

    Can someone help me to understand this piece of code please? its part of the TCP/IP api. What's the purpose of the macro __SOCKADDR_COMMON in the sockaddr struct ? does that macro apply to the data menbers of the struct ?

    Further more, what should I read to understand this coding format ? I've been reading C books but every time I get into Linux libraries I find myself in front of code that I can not understand...

    typedef unsigned short int sa_family_t;
    #define	__SOCKADDR_COMMON(sa_prefix) \
    sa_family_t   sa_prefix
    struct sockaddr
            __SOCKADDR_COMMON (sa_);	/* Common data: address family and length.  */
            char sa_data[14];		        /* Address data.  */
    Thanks to all.

  2. #2
    Join Date
    Jan 2009
    To put it in over-simplified terms: since C does not support inheritence, this is the closest thing you can do to achieving that result.

  3. #3
    Kernel hacker
    Join Date
    Jul 2007
    Farncombe, Surrey, England
    Why it is done like that, I have no answer to , but what it really means is that the struct looks like this:
    struct sockaddr
            sa_family_t   sa_;
            char sa_data[14];		        /* Address data.  */
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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