peter.kourzanov@xxxxxxxxx wrote:
> Dear gcc users and developers,
>
> This might be a stupid question, nevertheless...
>
> I've been wondering for a long time, why the behaviour of
> variable-length arrays w.r.t. the sizeof operator is different
> for local/auto variables and for function arguments (in C99):
>
> #include <stdio.h>
> void foo(int s, int a[s]) {
> printf("%u\n",sizeof a);
> }
> int main()
> {
> int s=10,a[s];
> printf("%u\n",sizeof a);
> foo(sizeof a/sizeof a[0],a);
> }
>
> The printf's produce very different results: the first one
> returns "40" the other one returns 4, implying that the compiler
> forgets that the size of the array is actually "s", not the size
> of the pointer argument. Is it so difficult to make "sizeof a"
> return "s" in both cases?
That's C for you, I'm afraid: arrays always decay to pointers to the
first element when passed as arguments. The size of a VLA is not passed.
Andrew.
