How do I wrap several C++ unmanaged classes into a single COM Object?
This might seem like a silly question, but it's been a (long) while since I've been in the world of Microsoft COM.
I've got a couple of classes (FooA and FooB) which are part of a static unmanaged C++ library.
Rather than figuring out the nightmare of header file inclusion resolution, I'd like to wrap this library in a COM object.
Doing so would make the library available for consumption by C# (managed) clients.
The 1st pass of the COM object is to be single thread apartment (we might switch to multi thread later).
This is where I'm a little rusty and get a little confused.
I have classes FooA and FooB contained in the library.
FooA and FooB have methods which I'd like to expose to clients.
class FooA {
Method1;
Method2;
}
class FooB {
Method3;
Method4;
}
How do I expose those classes and methods their methods through a COM interface?
Ultimately I need an instantiation of the class (an object) to reference methods on that object.
Do I need to return and pass around a ptr to the instantiated object to interfaces exposed on the COM object?
A lot of the examples I've seen are pretty standard: add/multiply two integers
Can someone shed some light on this for me and perhaps point me towards a useful example?
Thanks,
JohnB
I've got a couple of classes (FooA and FooB) which are part of a static unmanaged C++ library.
Rather than figuring out the nightmare of header file inclusion resolution, I'd like to wrap this library in a COM object.
Doing so would make the library available for consumption by C# (managed) clients.
The 1st pass of the COM object is to be single thread apartment (we might switch to multi thread later).
This is where I'm a little rusty and get a little confused.
I have classes FooA and FooB contained in the library.
FooA and FooB have methods which I'd like to expose to clients.
class FooA {
Method1;
Method2;
}
class FooB {
Method3;
Method4;
}
How do I expose those classes and methods their methods through a COM interface?
Ultimately I need an instantiation of the class (an object) to reference methods on that object.
Do I need to return and pass around a ptr to the instantiated object to interfaces exposed on the COM object?
A lot of the examples I've seen are pretty standard: add/multiply two integers
Can someone shed some light on this for me and perhaps point me towards a useful example?
Thanks,
JohnB
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Hard to say anything about performance overhead, which could be from marginal to significant depending on the usage pattern among other things. Marshaling and Apartments would definitely be a lot slower than direct native calls.
In most cases a benchmark would help develop a sense of performance overhead.
In most cases a benchmark would help develop a sense of performance overhead.
ASKER
Given the existing architecture, I'm stuck using unmanaged C++.
This COM object is to be consumed by other unmanaged C++ libraries.
My thought was to encapsulate the implementation through COM.
I could have always included the full blown integrated library (and all it's supporting libraries) directly
with the other libraries.
My idea was that the performance overhead of calling a COM object from an unmanaged C++ client
should be only marginally worse than including the library directly (I guess that this depends on the marshaling
of the parameters). Thoughts?