Hi,
Ian Lance Taylor <i...@google.com> skribis:
> ludovic.cour...@inria.fr (Ludovic Courtès) writes:
>
>> I understand. However, I’m concerned about keeping the information at
>> compile-time. For example:
>>
>> extern void foo (int a, int x[a]);
>> static void bar (void) {
>> int x[123];
>> foo (456, x);
>> }
>>
>> Here the compiler could emit a diagnostic in ‘bar’.
Oh, and within ‘foo’ itself:
int foo (int a, int x[a])
{
return foo[a + 23]; /* <- warning here */
}
> I see. That seems to have some potential. It would be a gcc extension,
> of course. Perhaps something like
>
> extern void foo (int a, int x[__attribute__ ((dim (a)))])
>
> could be implemented.
Why use special syntax for this? It seems to me that ‘int x[a]’ conveys
the exact same information.
> This would issue an error if foo were called such that the length of
> the x were not at least a. A serious problem with this approach would
> be that it is not reliable, since the caller of foo might not know the
> length of the array being passed as a pointer.
In that case the call site could just be ignored, or a “cannot determine
array size” warning could be issued.
> I suppose it would be possible to issue runtime checks when static
> checks don't work, and issue a compilation error in cases were no
> runtime check is possible. Without those checks I think the extension
> would be ill advised. With those checks I don't know how often it
> would usable in practice.
Yes.
Thanks,
Ludo’.
