marshal c++ reference to int

[jonpb]

Hi, I cannot find the correct attributes to marshal the following
unmanaged function signature:

void WINAPI GeomVec2AngleD( const Vector2RecD& v1, const Vector2RecD& v2,
double& angle)

I thought this would work:

[DllImport("xfor m400.dll")]
public static extern void GeomVec2AngleD([In] Point2D v1, [In] Point2D
v2, [In, Out] double angle);

Point2D's layout maps directly to Vector2RecD, there is no problem
there, the problem is, as soon as the C++ code attempts to write to
angle it throws a System.AccessVi olationExceptio n.

I tried a few more possible solutions but I cannot find the correct one.

Thanks

[Nicholas Paldino [.NET/C# MVP]]

Re: marshal c++ reference to int

jonpb,

You can not use references through the P/Invoke layer.

Rather, you will have to expose a function which takes pointers instead,
and marshal that function. Then, your function would just make the call to
the original function.


--
- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard. caspershouse.co m

"jonpb" <nospam@nospam. comwrote in message
news:ePlZJWrPJH A.764@TK2MSFTNG P05.phx.gbl...

Hi, I cannot find the correct attributes to marshal the following
unmanaged function signature:
>
void WINAPI GeomVec2AngleD( const Vector2RecD& v1, const Vector2RecD& v2,
double& angle)
>
I thought this would work:
>
[DllImport("xfor m400.dll")]
public static extern void GeomVec2AngleD([In] Point2D v1, [In] Point2D v2,
[In, Out] double angle);
>
Point2D's layout maps directly to Vector2RecD, there is no problem there,
the problem is, as soon as the C++ code attempts to write to angle it
throws a System.AccessVi olationExceptio n.
>
I tried a few more possible solutions but I cannot find the correct one.
>
Thanks

[Ben Voigt [C++ MVP]]

Re: marshal c++ reference to int



"jonpb" <nospam@nospam. comwrote in message
news:ePlZJWrPJH A.764@TK2MSFTNG P05.phx.gbl...

Hi, I cannot find the correct attributes to marshal the following
unmanaged function signature:
>
void WINAPI GeomVec2AngleD( const Vector2RecD& v1, const Vector2RecD& v2,
double& angle)
>
I thought this would work:
>
[DllImport("xfor m400.dll")]
public static extern void GeomVec2AngleD([In] Point2D v1, [In] Point2D v2,
[In, Out] double angle);
>
Point2D's layout maps directly to Vector2RecD, there is no problem there,
the problem is, as soon as the C++ code attempts to write to angle it
throws a System.AccessVi olationExceptio n.
>
I tried a few more possible solutions but I cannot find the correct one.

You should use "ref" on the angle parameter.

>
Thanks