Re: "span"

Em 3/22/2024 9:19 PM, Ben Bacarisse escreveu:

Thiago Adams <thiago.adams@gmail.com> writes:
 

On 22/03/2024 08:30, Stefan Ram wrote:

    Some people suggested to introduce a feature "span" (probably a
    type) into C++, so that when one has an int array "a" and calls
    "f( a )", the length of a is being transferred to "f", which "f"
    is defined using "void f(span<int> a)". The "span" in "f" then
    knows the length of "a". This is supposed to be less error prone
    than passing a pointer with a separate length argument.
    Of course, I immediately wondered whether one could implement
    such a "span" for C, and here's a draft:
#include <stdio.h>
#define SPAN_PARAM(x,a,n) x*a,size_t const n
#define SPAN(a) a,(sizeof a/sizeof 0[a])
void print( SPAN_PARAM( int, a, n ))
{ for( size_t i = 0; i < n; ++i )
    printf( "%lld: %d\n", i, a[ i ]); }
int main( void )
{ int a[ 3 ]={ 4, 6, 8 };
    print( SPAN(a) ); }
    . But since C is another language, there are other forces at work,
    which means that the overall usability of such macros in C might not
    make their definition and use worthwhile. Of course, the "smart" span
    type in C++ surely can do more than my simple macros can do in C!

>
>
(
C++ proposals use new type<T> instead of qualifiers. This creates a big
mess on the type system and incompatibility with C.
I don't have idea how/why they do this constantly.
)
>
C does not need this for parameters since the current array syntax already
cover that.
>
void f(int n, int a[n])

 Although you can't rely on this anymore since it's now an optional part
of the language.

I think it is back in c23.
But not vlas.

...

C already have a syntax for pointer to array
>
int (*)[2] p;

 I think you mean
    int (*p)[2];
 

yes.