Thread: 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...

Code:

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.

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.