Re: about struct in_addr

[Guy Harris <guy () alum mit edu>]

Lan Qing wrote:
> hello,
> I read the fllowing words in the c header file <netinet/in.h>

I.e., the header that came with your OS, not the header that comes with 
tcpdump?

> /* Internet address.  */
> typedef uint32_t in_addr_t;
> struct in_addr
>  {
>    in_addr_t s_addr;
>  };"
> the struct in_addr have only one variable in it, is there any necessary to
> define a struct like that?
> why not use "typedef in_addr_t in_addr;" directly?

In BSD, it was originally a union that also included arrays of bytes so 
that code could look at the bytes, for dealing with class A, B, and C 
Internet addresses - as the comment in OS X, and other BSDs, says, it's 
"a structure for historical reasons", because code depended on there 
being an "s_addr" member (which was one of the members of the union).
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