I think it is off-topic for SG16 to discuss this proposal at all.
There are no encoding concerns beyond those already answered for
std::format, and what the components of a std::fpos<T> are and
which sequence of characters is used to represent it and whether
you can (hypothetically) parse the representation to recover a
std::fpos<T> are all good questions --- that belong to LEWG, not SG16.

And a data point: The convertibility requirement for std::fpos to
std::streamoff (C++98) predates the introduction of explicit conversion
operations (C++11), thus the only way to reasonably satisfy the explicit
conversion requirement was for implementations to provide an implicit
conversion.

Jens


On 23/10/2024 02.06, 梁家铭 via SG16 wrote:
> Hi Corentin,
>
> The first version of draft (D3374R0) is to format the `fpos` as an integer directly, which can be confirmed by Victor. The reason why I finally add the state type is that Tom reminds me that it's not proper to neglect such a basic component by default and I think that really makes sense. This also makes me reflect that it's possibly not robust for stream to only output the integer, and that's why `.offset` is not thought as the solution. There is no difference for me to cast explicitly or call `.offset`.
>
> In today's talk, I'd like to share something about:
> + briefly cover what mbstate_t should do, as you may be already familiar with;
> + why C++ programmers generally think it's enough to use the integer, as a result of illusion from the implementations of streams that do text encoding;
> + we could provide such facility in the standard library for those programmers who concern the state, as long as we think mbstate_t is not a deprecated feature.
>
> For the formatting specification, there could be some better representations if `(pos, mbstate)` is not considered as a good one or even not the default one, and I'd like to discuss with you :). I know that mbstate_t couldn't be expected to be formatted in any meaning way, but it's enough to make it recoverable by the implementation. For me doing a round-trip is possibly the most thing we could do in the standard.
>
> Thanks for the feedback,
> Liang Jiaming
>
>