> On 03 Dec 2015, at 1:43, Jens Alfke <[email protected]> wrote:
>
> If x is a value of class/struct X, and y is a non-virtual method, then x.y()
> turns into X::y(&x).
>
> So putting the two together, if x is a pointer to X, then x->y() turns into
> X::y(x). There’s no pointer dereference involved, and no issue if x is NULL.
> All that happens is that in the implementation of y(), `this` will be NULL.
Is that standard-mandated behaviour or an optimization? If it is legal for any
member function call to go via the this pointer, then the check is illegal. As
a practical consideration, in this example (modified from the viva64 post to
add a data member to the second base class), Xcode 7.1.1 produces a non-null
this pointer from a null pointer call:
#include <stdio.h>
class FirstBase {
int firstBaseData;
};
class SecondBase {
int secondBaseData;
public:
void Method()
{
if( this == 0 ) {
printf( "this == 0\n");
} else {
printf( "this != 0 (value: %p)\n", this );
}
}
};
class Composed1 : public FirstBase, public SecondBase {
};
int main()
{
Composed1* object = 0;
object->Method();
}
-a
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