Question

Recently I saw following piece code:

if ((rgb = (fp16 *)malloc(width*height*sizeof (*rgb)*3)) == NULL)

rgb is declared as a pointer of some class type.
In the above code, malloc() is taking arguments which is width*height*sizeof(*rgb)

So it is some kind of self referential initialization(If i may call it by giving this name!)
i.e. belore rgb pointer is allocated by malloc, it is dereferencing it in call to malloc.

In this particular code, i saw that the pointer rgb is not initialized to NULL or anything.

What would be the behaviour of such code.

• Normal functioning or

• Crash due to null pointer dereference, or a

• Garage pointer dereference

thanks,

-AD.

Answer 1

sizeof does not evaluate its operand, so in this case sizeof(*rgb) will return the size of rgb‘s type, which I assume is fp16 *.

Completely valid C code.

If it did evaluate it and the pointer was just some declared pointer with no initialized value, then you would get undefined behavior.