Re: [lwip-users] struct ip_addr VS struct in_addr

[Jonathan Larmour]

Ceresoli Luca wrote:
> For this I am trying to remove lwIP-specific code where possible from
> the API of my code. The most notable part of this work seems to be
> removing any usage of struct ip_addr (lwIP-specific), perhaps in favor
> of struct in_addr (portable).
[snip]
> int my_api_call(const struct in_addr *dst_in_addr, ...)
> {
>   struct ip_addr dst_ip_addr;
>   ...
>   memcpy(&dst_ip_addr, &dst_in_addr->s_addr, sizeof(dst_ip_addr.addr)); // 
> <---- look here
>   ret = udp_sendto(pcb, p, &dst_ip_addr, dst_port);
>   ...
> }
>
> I wonder if my approach is correct and if something better than
> memcpy() can be done (my CPU does not support unaligned access).

dst_in_addr will already be aligned, so does not need memcpy. You can just do:
dst_ip_addr.addr = dst_in_addr->addr;

However in the other direction - if there's an ip_addr you need to convert 
back to a struct in_addr, then you /would/ need memcpy, to safely 
guarantee alignment.

> A more fancy idea: rename the unique field of ip_addr from addr to
> s_addr, so one struct can be simply be type-cast to the other. I bet
> there's some packing issue about this
> (http://savannah.nongnu.org/bugs/?21664#comment4) but I'm quite unaware
> of API implementation so I can't judge.

Yes there would be a packing issue.

Jifl
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