On Wed, Jan 27, 2021 at 5:50 PM Steve Downey <sdowney@gmail.com> wrote:

The basic execution character set is the basic source execution character set plus the mandatory control codes, and is what you need to express the mandatory C characters in the execution space, without discussing what the encoding actually is. When there was much wider variance in what character sets included which characters it was far more important in figuring out how to port the language. 

If there was a theoretical encoding that had no bell for example, would that break C++ in anyway?

 

On Wed, Jan 27, 2021 at 4:04 AM Corentin via SG16 <sg16@lists.isocpp.org> wrote:

On Wed, Jan 27, 2021 at 9:59 AM Peter Brett <pbrett@cadence.com> wrote:

Hi Corentin,

 

This certainly seems like a possible simplification to me. Out of interest, did you manage to find out *why* the concept of the basic execution character set was added to the standard in the first place?

Alas I didn't, but it goes back to at least C89

 

 

                      Peter

 

From: SG16 <sg16-bounces@lists.isocpp.org> On Behalf Of Corentin via SG16
Sent: 27 January 2021 08:57
To: SG16 <sg16@lists.isocpp.org>
Cc: Corentin <corentin.jabot@gmail.com>
Subject: [SG16] Is the concept of basic execution character sets useful?

 

EXTERNAL MAIL

Hello,

 

Very quick reminder, using C++20 terminology

We have:

 

- basic source character set, which, while of limited use in the core language is used quite a bit in the library as a proxy for  "displayable characters available in all encodings", which removal would then be slightly more involved.

 

- The execution character set(s) which describe actual character sets used during evaluation and are therefore necessary.

 

- The basic execution character set, which is a super set of the basic source character set

and a subset of all execution character sets.

 

It's strictly basic source character set +  alert +  backspace + carriage return + NULL

 

Nowhere is it used in the library.

It is not used in the core language either, except of course that we need to prescribe that NULL is encoded as 0 and that digits are encoded sequentially.

 

While  alert +  backspace + carriage return are mentioned in escape sequences, if a theoretical encoding would miss these characters, there would be no further ill-effect on the behavior of the standard.

 

The main change on top of the C++20 wording would be as follow

 

The basic execution character set and the basic execution wide-character set shall each contain all the members of the basic source character set, plus control characters representing alert, backspace, and carriage return, plus a null character (respectively, null wide character), whose value is 0. For each basic execution character set, the values of the members shall be non-negative and distinct from one another. In both the source and execution basic character sets, the value of each character after 0 in the above list of decimal digits shall be one greater than the value of the previous. The execution character set and the execution wide-character set are implementation-defined supersets of the basic execution character set and the basic execution wide-character set, respectively. The values of the members of the execution character sets and the sets of additional members are locale-specific.

 

Any reason why we should not do this?

 

(As always, I'm interested in having a simple model with no unnecessary terminology as, as observed these past few months, it has a tendency to hinder our collective understanding)

 

Corentin

 

 

 

 

 

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