Re: "A diagram of C23 basic types"

On 03/04/2025 05:43, Janis Papanagnou wrote:

On 02.04.2025 09:32, Kaz Kylheku wrote:

On 2025-04-02, Janis Papanagnou <janis_papanagnou+ng@hotmail.com> wrote:

On 02.04.2025 07:59, Alexis wrote:

>
Thought people here might be interested in this image on Jens Gustedt's
blog, which translates section 6.2.5, "Types", of the C23 standard
into a graph of inclusions:
>
   https://gustedt.wordpress.com/2025/03/29/a-diagram-of-c23-basic-types/

>
A nice overview. - I have questions on some of these types...
>
The _Decimal* types - are these just types with other implicit
encodings, say, BCD encoded, or some such?

>
IEEE 754 defines decimal floating point types now, so that's what
that is about. The spec allows for the significand to be encoded
using Binary Integer Decimal, or to use Densely Packed Decimal.

 Thanks for the hint and keywords. It seems my BCD guess was not far
from what these two IEEE formats actually are.
 Does that now mean that every conforming C23 compiler must support
yet more numeric types, including multiple implementation-versions
of the whole arithmetic functions and operators necessary?
 

They are an optional feature (as are the other floating point and complex types beyond the basics of float, double and long double).

I wonder why these variants had been introduced.

I presume that some people want them.  They are in the ISO 60559 standard, along with things like "interchange" floating point types intended to be maximally consistent between different systems.

 In many other languages you have abstractions of numeric types, not
every implicitly encoding variant revealed an the programming level.
 

That's often fine within a program, but sometimes you need to exchange data with other programs.  In particular, C is the standard language for common libraries - being able to reliably and consistently exchange data with other languages and other machines is thus very important.