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Ints versus Shorts in C# Apollo Wrapper

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Dan Noel (VIP)

I am working on project that involves numerous calls to a COM C++ program
that declares numerous parameters and return types as 16 bit shorts.

When we automatically generated a C# wrapper using tlibimp those short
parameters show up as int16 declarations.

When writing our C# wrapper, a colleague insists that we can use (ints) for
these 16 bit values in all of our wrapper code ... I am somewhat skeptical.
So far, we have not tested all the code, but apparently the marshaller is
able to translate from C++ shorts to ints.

My colleague wants ints on the C# end of the world because, he does not want
the C# programmer to need to worry about short declarations. The code is
easier to work with when everything takes an int. I agree with him on this
point, but I worry that we will get into trouble at some point with this type
of coding practice. Perhaps, we are just lucky that we have not had a problem
up to this point by using ints for our C# wrappers for our C++ shorts.

I would greatly appreciate some commentary from some C# interop gurus on
this point.

How do you declare your C# code which references C++ 16 bit integer values ?
Will we eventually run into problems by declaring our C++ shorts as C# ints ?

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Robert Jordan

Hi Dan,

[Original message clipped]

AFAIK, that kind of "retyping" will only work, when you apply
the appropiate marshalling attributes:

C++:
short method(short arg);

C#
[return: MarshallAs(UnmanagedType.I2)]
int method(
[MarshallAs(UnmanagedType.I2)] int arg
);

bye
Rob

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Robert Jordan

[Original message clipped]

MarshalAs ;-)

bye
Rob

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Dan Noel (VIP)

Thanks for the response

Is there any chance this type of Marshaling happens implicitly ?

I am trying to figure out why we have not seen any problems doing this type
of conversion.

Dan

"Robert Jordan" wrote:

[Original message clipped]

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Dot Net Guruias Sjögren

Robert,

[Original message clipped]

You can't change the way an int is marshaled with MarshalAs, it's a
blittable type that will always be copied as 32 bites of data (for
performance reasons, among other things). If you try it you get a
MarshalDirectiveException.

Dot Net Guruias

--
Dot Net Guruias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

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	System.Runtime.InteropServices.MarshalDirectiveException
	System.Runtime.InteropServices.UnmanagedType

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