Re: [boost] [endian] Refresh based on comments received

From: Christopher Kohlhoff (chris_at_[hidden])
Date: 2006-06-05 21:42:01

Hi Yuval,

Yuval Ronen <ronen_yuval_at_[hidden]> wrote:
> I see that enum endianness have a 'native' option. This looks
> a bit weird to me. If I want to use native endianness, why
> should I use a class named 'endian'?

You might be writing code that cares about endianness, and need
to use native endianness in some places, and big- or
little-endian integers in others.

One example is receiver makes right protocols, where the message
is always transmitted using the sender's endianness. When a
message is received it could be either big- or little-endian.

> - Is aligned more common than unaligned, or vice-versa? It
> sounds logical to me, that since the POD integers types (int
> and friends) are aligned, it should also be the 'default'
> behavior of any class mimicking them, including of course, the
> endian class. The conclusion is that instead of prefixing 'a'
> or 'aligned_' to the aligned types, the unaligned types should
> get a prefix ('unaligned_'?).

I had a think about this too, and came to the opposite
conclusion that unaligned is the sensible default. The purpose
of these classes is manipulating records for I/O, not mimicking
in memory structures. IMHO defining a structure that uses the
aligned endian types (slightly) increases code fragility due to
the effect of compiler alignment options on the layout, and so
should not be given equal billing. Since the stated motivation
for supporting aligned types is performance, you'd have specific
reasons for choosing them and be more likely to be careful about
using them correctly.

Cheers,
Chris