Thread: my code breaks unique pointer rule?

Sorry Mats,


I do not fully agree.

You mentioned,

"so the function is guaranteed that the data from the "unque" pointer is not reachable from any other pointer"

But the data pointed by ptr1 could be reached by ptr2 in main.

"this is a gurantee that the paraemeter coming into the function is unique"

Not unique, ptr1 and ptr2 point to the same memory.

Any comments?

Originally Posted by matsp

Yes, so the function is guaranteed that the data from the "unque" pointer is not reachable from any other pointer - this is a gurantee that the paraemeter coming into the function is unique, not necessarily that it actually is unique inside the function.

--
Mats

regards,
George

Thanks CornedBee,


I do not think compiler checks anything before passing the parameters. I have modified the sample and posted the code below.

You can see ptr1 and ptr2 are aliasing in main. Compile and run ok, any comments?

Code:

__interface IFoo {

public:

	virtual int foo ([unique] char  *ptr1, [unique] char  *ptr2) = 0;
};

class Foo : public IFoo {

public:

	int foo (char  *ptr1, char  *ptr2)
	{
		char array1[] = "Hello";

		ptr1 = array1;
		ptr2 = array1; // should be wrong, no aliasing allowed, but compile and run ok
		
		return 0;
	}
};


int main()
{
	char buf1[] = "Hello World! \n";
	char* ptr1 = buf1;
	char* ptr2 = ptr2;

	Foo f;
	// f.foo(ptr1, ptr2);
	f.foo(ptr1, ptr1);

	return 0;
}

Originally Posted by CornedBee

The compiler only checks what happens when you pass the pointers. It doesn't care what you do with them afterwards.

regards,
George

Thanks Mats,


You mean it is just an indicator to developer of function and the user of the function to be aware more of the attribute of parameter/return value, but compiler/linker/runtime will never force anything more than the situation when you do not put any additional attibute, right?

If yes, let me know if you have found any formal documents from MSDN or something else where which indicates the above points. I am also looking for the documents, but have not found any formal ones. :-)

Originally Posted by matsp

Yes, so I don't think the compiler checks - you are just obliged to follow the rules.

--
Mats

have a good weekend,
George