The Weird and The Wonderful

Nemanja Trifunovic wrote:

NULL only if you explicitly set it to NULL - an unitialized pointer is not going to be NULL

PIEBALDconsult wrote:

If you don't assign NULL to pointer variables when freed then you're on your own.

PIEBALDconsult wrote:

C99 and C# initialize pointers (references) to NULL

Dave Kreskowiak wrote:

what's the default for a newly created, but uninitialized pointer??

PIEBALDconsult wrote:

But I expect that if it isn't NULL already it soon will be.

Nemanja Trifunovic wrote:

why checking for 0 only?

ASSERT(0 == ((DWORD_PTR)pAddress & 3));

PDWORD pAddress = (PDWORD)&SomeFunction;
DWORD_PTR pInstructions = *pAddress;

MEMORY_BASIC_INFORMATION mbi;
if(VirtualQueryEx(GetCurrentProcess(),(LPVOID)pInstructions,&mbi,sizeof(MEMORY_BASIC_INFORMATION)))
{
	if(mbi.Protect & PAGE_EXECUTE_READ &&
		mbi.State & MEM_COMMIT &&
		mbi.AllocationProtect & PAGE_EXECUTE_WRITECOPY &&
		mbi.Type & MEM_IMAGE)
	{
		(*this.*SomeFunction)(val);
	}
}

Nemanja Trifunovic wrote:

I think I already demonstrated

PIEBALDconsult wrote:

But in that example you didn't set the pointer to NULL and you know it.

PIEBALDconsult wrote:

A called method should not free something that was passed in, or if it's expected to, you'll need double indirection.

Find a better example, that one's a coding horror on its own.

{
  int arr[5];
  int *p;
  int i;

  p=arr;
  for (i=0; i<5; i++)
    *p++ = i;
}

PIEBALDconsult wrote:

I think it's more a question of, if you write a function (perhaps a library function) that takes one or more pointers, do you check them for null or let them blow up? And why?

1. Is the operation in the null-pointer situation defined by the interface standard?
   
   
2. Would the null-pointer situation have a logical meaning (e.g. it may be useful for a function that reads data from a stream to have an option to simply throw away some data; allowing the function to take a null pointer for such usage may be more elegant than requiring the use of a separate function)?
   
   
3. Are there any circumstances that could case a null pointer to be passed in accidentally?
   
   
4. How would the probable consequence of passing in a null pointer compare with the best result one could achieve?