C++/CX Header file can't find Microsoft namespace - visual-studio-2013

Question

I have a header file with the following code:
Microsoft::WRL:ComPtr<ID3D11Device2> m_device;
inside a class definition. Visual Studio 2013 is saying that Microsoft is not a namespace, if I take the code and cut it out and put it in another class in another file unchanged it works just fine!
Any ideas?
Philip
EDIT: All of a sudden (without me having changed anything) Intelissense now accepts Microsoft::WRL::ComPtry as valid but when I compile it still gives me errors that it does not exists.

Answer 1

You need to
#include <wrl.h>
or
#include <wrl/client.h>
To get Microsoft::WRL::ComPtr in your module.
When you say "Visual Studio 2013 is saying that Microsoft is not a namespace" do you mean you get a compiler error or is just Intellisense? When dealing with headers, Intellisense can get a bit out of sync until you build again. For example:
//Test.h
class A { Microsoft::WRL::ComPtr<T> a; };
//Test.cpp
#include <wrl/client.h>
#include "Test.h"
If you just added the #include <wrl/client.h> to the Test.cpp, Intellisense might not know yet it is in scope for the header. It's perfectly valid C++ already, but a better practice is to include in your headers the ones it needs like:
//Test.h
#pragma once
#include <wrl/client.h>
class A { Microsoft::WRL::ComPtr<T> a; };
The other way this sync issue can manifest itself is if you are doing:
//Test.h
class A { Microsoft::WRL::ComPtr<T> a; };
//Test.cpp
#include "pch.h"
#include "Test.h"
//pch.h
#include <wrl/client.h>
Again, fully valid C++ that will build. Intellisense knows it works when you build, but might not until then.
Note: WRL is traditional C++ and is not using C++/CX language extensions. They both exist to make it easier to consume WinRT APIs from C++, and you will see the Microsoft::WRL::ComPtr used inside C++/CX applications when dealing with non-WinRT COM APIs like Direct3D. And you can mix C++/CX with WRL in the same application taking advantage of the fact that you can use reinterpret_cast<> between C++/CX ref ^ and ABI COM pointers. You can use Microsoft::WRL::ComPtr in old-school Windows desktop apps on Windows 7 or Windows Vista too.
With all that said, WRL and C++/CX are two distinct things.
Update: For consuming Windows Runtime APIs, you can also use C++/WinRT which is also 'standard' C++ without any need for the C++/CX extensions. See Microsoft Docs. You can use Microsoft::WRL::ComPtr for C++/WinRT applications, or you can use their variant wrl::com_ptr