Question

I’m programming Windows COM in C++ and I see that a lot of functions get prefixed with :: so that the global namespace version got called. Why is that?

I understand that there may be conflicts with namespaces, but does it happen so often in COM that everyone has become so paranoid that every single function now has to be resolved explicitly?

Here are some examples that I see often:

wStrLen = ::SysAllocStringLen(NULL, wStr);
::SysFreeString(str);
::CoTaskMemFree(item);

And many others.

It just puzzles me why the programmers chose to resolve namespace explicitly and why they didn’t just write:

wStrLen = SysAllocStringLen(NULL, wStr);
SysFreeString(str);
CoTaskMemFree(item);

Any ideas?

Answer 1

No, that’s not common in COM programming, not in any I wrote or studied anyway. COM itself adds few names to the global namespace, there are not that many helper functions. A common way to implement a COM interface is to use a C++ class, you can stick it in any namespace you like since it doesn’t get exposed at all outside of the module. I suspect that it is just something the team whose code you saw preferred. If you saw it in a book then that’s a good way to increase the odds that the book code sample can drop into an existing program without too much trouble. There’s otherwise nothing wrong with it.