Re: "span"

ram@zedat.fu-berlin.de (Stefan Ram) writes:

  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])

The usual reason given for writing 0[a] in a macro is so that
parentheses are not needed as they would be (recommended) for *(a) or
(a)[0].  But since you don't seem to care about writing a rather than
(a) I don't see why you wrote 0[a] rather than either *a or a[0].

void print( SPAN_PARAM( int, a, n ))
{ for( size_t i = 0; i < n; ++i )
  printf( "%lld: %d\n", i, a[ i ]); }

What happens when print wants to pass 'a' to another function that takes
a span?

int main( void )
{ int a[ 3 ]={ 4, 6, 8 };
  print( SPAN(a) ); }

--
Ben.