what does "::functionName()" imply in c++?

Question

I came across a piece of code which looks like this:

::GetSystemDirectory(buffer, MAX_PATH);

I've never seen a function call preceded by an empty ::. I've always seen them being used with namespaces.

Can someone please explain me what does an empty :: mean ?

@Rapptz What if I just call the function without it ? Will it only restrict it to current namespace ? — brainydexter, Jun 10 '13 at 08:51

score 8 · Accepted Answer · answered Jun 10 '13 at 08:51

8

It's the scope resolution operator. With nothing in front of it, it indicates global scope.

So for instance, suppose you have a class that defines its own GetSystemDirectory method. Within the code of a method of that class, to call the global one, you'd need the :: in front of it, otherwise by default you'd get the one specific to the class. (And similarly for namespaces.)

answered Jun 10 '13 at 08:51

T.J. Crowder

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I believe, it would make most sense to call the system functions with the `::` then ? – brainydexter Jun 10 '13 at 08:57
@brainydexter: I haven't done enough C++ in the last 15 years to really have an opinion on that. *Sounds* reasonable. :-) – T.J. Crowder Jun 10 '13 at 08:59

what does "::functionName()" imply in c++?

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