declaration/definition and instantiation of COM objects with visual c++?

Question

i need to instantiate com object which is .dll and on local machine in visual c++,i know that it can be done by using CoCreateInstance("clsid") ,but i am confused about declaration.so can anyone explain all steps involved? for late binding as well as early binding

is any import/inclusion required
how to declare com object ?
any other steps required before createinstance (e.g CoInitialize?)

or provide any specific reference involving step by step code

thanks LihO and Seva both of your answers are really helpful, both shows two different ways, #import is more efficient but i can't find typelib of one of object,i am confused which answer i should accept as both are correct. — user1176743, Feb 02 '12 at 07:10

LihO · Accepted Answer · 2012-01-31T22:25:05.767

0

First you have to call CoInitialize and don't forget to callCoUnitialize if initialization was successful.

So your code will have the following structure:

HRESULT hr = CoInitialize(NULL); 
if (SUCCEEDED(hr))
{
    try
    {
        CoCreateInstance(...)
        // ...
    }
    catch (_com_error &e)
    {
        //...
    }
    CoUninitialize();
}

For more information visit MSDN. I recommend you to start with The COM Library and then you should read something about CoInitialize and CoCreateInstance functions before you use them.

This tutorial could help you too: Introduction to COM - What It Is and How to Use It.

edited Jan 31 '12 at 22:25

answered Jan 31 '12 at 19:55

LihO

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I remember the pair CoInitialize/CoUninitialize should be used, say, in main. If CoInitialize fails, there is little point in further process. Your answer suggests to call before each CoCreateInstance. – CapelliC Feb 01 '12 at 14:55
Yes, it is initialization of COM Library, that allows you to create instance of COM and work with it. – LihO Feb 01 '12 at 15:35

Seva Alekseyev · Answer 2 · 2017-10-14T19:39:51.127

#import is very much recommended. if you import the typelib with #import, you'll be using the Native COM framework, which isolates some gritty details and makes life generally easier.
In Native COM, something like this:

LibName::IMyInterfacePtr pInterface;

In raw C++:

IMyInterface *pInterface;

But see above.

Call CoInitialize() in the beginning of the program, CoUninitialize() in the end. if running inside a DLL, then it's much more complicated.

declaration/definition and instantiation of COM objects with visual c++?

2 Answers2