Problem with C++ DLL returning bool

[Thorsten Dittmar]

Hi there,

we have this C++ DLL we wrote some time ago to do some Win32 native
stuff for us.

The function we're calling in the DLL returns a boolean value (type
bool) indicating success of the operation.

We declare the import in C# like follows:

DllImport("xyz.dll")]
private static extern bool DoSomething(...);

We call the function like this:

bool result = DoSomething(...);

Now: we're using this in Visual Studio 2008. When we set the target
framework version to 2.0 everything works fine - the function returns
false, the result-variable has the value false.

As soon as we switch the target framework version to 3.5 (no other
changes to the project), the C++ function still returns false, but the
result-variable is set to true!

How could that be?

As a workaround we've change the result type from bool to int, returning
defined values for success or failure, but this is not very satisfactory...

Any advice?

Thanks
Thorsten

[Willy Denoyette [MVP]]

"Thorsten Dittmar" <td******@altenbrand.dewrote in message
news:O1**************@TK2MSFTNGP03.phx.gbl...

Hi there,

we have this C++ DLL we wrote some time ago to do some Win32 native stuff
for us.

The function we're calling in the DLL returns a boolean value (type bool)
indicating success of the operation.

We declare the import in C# like follows:

DllImport("xyz.dll")]
private static extern bool DoSomething(...);

We call the function like this:

bool result = DoSomething(...);

Now: we're using this in Visual Studio 2008. When we set the target
framework version to 2.0 everything works fine - the function returns
false, the result-variable has the value false.

As soon as we switch the target framework version to 3.5 (no other changes
to the project), the C++ function still returns false, but the
result-variable is set to true!

How could that be?

As a workaround we've change the result type from bool to int, returning
defined values for success or failure, but this is not very
satisfactory...

Any advice?

Thanks
Thorsten

If you are sure that the C function returns a bool, and not a BOOL, then it
should work, else you should marshal the return value using:

[return: MarshalAs(UnmanagedType.Bool)]
Willy.