How do I set up a CAutoPtr to call a class method in C++ from my dll?

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C++

ATL

I used the Visual C++ > ATL Project wizard to create a COM dll in Visual Studio 2013. I then used the ATL Simple Object Wizard to create an object in that dll with the following names.

C++
Short name: "PT2_B_db" .h file: "PT2_B_db.h"
Class: "CPT2_B_db" .cpp file: "PT2_B_db.cpp"
COM
Coclass: "PT2_B_db" Type: "PT2_B_db Class"
Interface: "IPT2_B_db"

I want to use a CAutoPtr to call methods from my dll class in C++. I was thinking of something like this from my C++ calling project:

CPT2_B_db* pClassObject = new PT2_B_db();
CAutoPtr<cpt2_b_db> spClassObject(pClassObject);
spClassObject->SomeClassMethod();

How do I set this up in the C++ project from which I want to do the calling?
Where do I reference what header files, etc.?

The dll works from my projects that use VBA. I'm searching for the C++ implementation that's analogous to this:
1.) From VBA, I set the Tools > References to include "PT2_BLib".
2.) Then I include the code:

Dim objPT2_B As Object
Set objPT2_B = New PT2_BLib.PT2_B_db
strDoubleValue = objPT2_B.DoubleValueString(dblInputValue, strFormatString)

-and it works just fine. Any help you could give in porting this same VBA functionality to C++ would be appreciated.

Thanks!
Carl Olen