double semicolon in front of a function call??

Hi,

I was reading "Inside COM" book published by Microsoft Press, and one of the examples
in the book of client implementation had following codes.

#include <Iface.h>
#include <objbase.h>
...
HRESULT hr = ::CoCreateInstance(...arguments...);

In this code, why was double semicolon "::" placed in front of CoCreateInstance(...)?
I saw this in numerous occasions, but I could not find a good document stating
this issue. I would very much appreciate for your help.

Firstly, it's not semicolon, it's just colon (I think that's what it's called anyway). ; is semicolon.
Anyway, it merely tells the compiler to look for the function inside the global namespace. I doubt it's necessary here; it's more of a programming style.

Oh yeah, I used wrong words there. Thank you for clarifying it for me. Now it's all clear.

I guess it might be useful to clear up ambiguous situations such as the following:

Code:

---

#include <iostream>

namespace my_names
{
    void foo() { std::cout << "my_names::foo()\n"; }
}

void foo() { std::cout << "foo()\n"; }

int main()
{
    using namespace my_names;
    //foo();  //error, which foo() to use?
    ::foo();  //foo()
    my_names::foo(); //my_names::foo()
}

---

In the book it is probably more like a style issue as Elysia says.