On Tue, Feb 22, 2011 at 12:34 AM, prabhu [off-list ref] wrote:

Jose Celestino wrote:

On Seg, 2011-02-21 at 21:41 +0530, prabhu wrote:


Hi all,

Could anyone please explain the use sin_zero in sockaddr_in?



Padding to allow for casting.



Hi Jose,

Could u please elaborate little more... why we? need this 8 byte padding.

My complete Question:
1. Actually total size of sockaddr_in is 16 byte and out of 16 byte why we
have to use 8 byte for padding.?
2. Do we use these 8 byte for any other usage for real time?

Unix network programming chapter 3.2 says that, "The POSIX specification
requires only three members in the structure: sin_family, sin_addr, and
sin_port. It is acceptable for a POSIX-compliant implementation to define
additional structure members, and this is normal for an Internet socket address
structure. Almost all implementations add the sin_zero member so that all socket
address structures are at least 16 bytes in size. "

It's kinda like structure padding, maybe reserved for extra fields in the
future. You will never use it, just as commented.