
Title	COM with smart pointers (Within single function)
Summary	Use this method to instanciate a COM object without having to call CoCreateInstance. This is suitable only if the object is created and destroyed withing the same function.
Contributor	John McTainsh
Published	9-Sep-2000
Last updated	2-Aug-2001

Page rating	82% for 15 votes	Useless Brilliant

Description.

Smart pointers are a relatively simple method of accessing COM objects. They encapsulate much of the tricky code required to instantiate and use a COM object.

Where do the names come from?

The name of the items in this example can be found in the tlh file and class factory as follows;

Name here	Purpose	How to find
`TrickyCom.exe`	Name of the file containing the object. May be a DLL or EXE.	Path and name of file.
`TRICKYCOMLib`	This is the Library name space	The namespace is located in `.tlh` and begins with `namespace` and ends with `...Lib {`
`ICtrlFlasherPtr`	Smart pointer name	Look in `.tlh` and add `Ptr` to the end of the first parameter in `_COM_SMARTPTR_TYPEDEF(ICtrlFlasher,`
`CtrlFlasher`	The coclass name	Look in `.tlh` and use the name defines in `struct /* coclass */ CtrlFlasher;`
`Increment()` and `Count`	The methods and properties	Look in `.tlh` for the `// Property data` and `// Wrapper methods for error-handling` sections

Solution.

In StdAfx.h add.

//Reference Com object to create *.tlh and *.tli
#import "C:\Temp\TrickyCom\Debug\TrickyCom.exe"
//The namespace is located in *.tlh and ends in ...Lib {
using namespace TRICKYCOMLib;

In Gizzmo.cpp in BOOL CGizzmoApp::InitInstance(); or any simular startup function that is called only once.

    //Initialise the application for use with COM objects
    HRESULT hr = CoInitialize( NULL );
    if( FAILED( hr ) )
    {
        AfxMessageBox( "CoInitialize failed\n");
        return FALSE;
    }

    //TODO Call CoUninitialize(); in the Destructor or other location
    //when all COM activity is completed.

Place this code where you want to access the object. ie In a button handler.

    //
    //Load Com object and use it
    //
    try
    {
        //Create the Common Object Model.
        ICtrlFlasherPtr pFlash( __uuidof(CtrlFlasher) );

        //Use the smart pointer
        TRACE( _T("Inital count = %d\n"), pFlash->Count );
        pFlash->Increment();
    }
    catch( _com_error e )
    {
        //Catch and display errors
        TRACE( _T("Com Error %x, %s\n"), e.Error, e.ErrorMessage() );
    }

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