Difference between @H and @H[0]

Question

I have

 var H: array of THandle;

then in a loop I create multiple threads, and assign thread handles to the elements of H, and then wait on them. Passing @H[0] as the 2nd parameter to WFMO below works.

WaitForMultipleObjects(Length(H), @H[0], True, INFINITE) <-- Works

But passing @H as below Fails with WAIT_FAILED. GetLastError returns "Invalid Handle".

WaitForMultipleObjects(Length(H), @H, True, INFINITE)  <--- Fails.

Why is @H different from @H[0] ?

Archipelago

Answer 1

1. Because it is a dynamic array, H is already a pointer and it points to the first element, so
2. @H[0] is the same as H - pointer to the first element
3. and now @H is equals to @@H[0] - pointer to pointer to the first element.

Lorrianelorrie

Thank you. So, if H was declared as H: array[0..10] of THandle then @H and @H[0] would be the same, I suppose. I can check it. – Archipelago

@Archipelago Yes, if H is a static array, than you need to get its address via @ operator and then @H is equals to @H[0]. – Lorrianelorrie

You can slso use POINTER(H) to get a pointer to the first element of the dynamic array. – Kurrajong