BUG: Exception error when you use a declare function that returns a date type in Visual Basic .NET 2003 and in Visual Basic .NET 2002 (327113)

SYMPTOMS

When a function in a DLL returns a date type and you call the function from a Microsoft .NET application by using PInvoke, you receive the following error message:

System.Runtime.InteropServices.MarshalDirectiveException : This method's type signature is not PInvoke compatible.

RESOLUTION

To work around this problem, you can declare the function to return a double value instead of returning a date, and you can then use the following method to get the date:

System.DateTime.FromOADate(ByVal d As Double) As DateTime

MORE INFORMATION

Steps to Reproduce the Behavior

Create a new Microsoft Visual C++ Win32 project named fnTest.
On the Application Settings tab, change Application type to DLL.

Paste the following code in Fntest.cpp:

extern "C"
{

	__declspec(dllexport) double fnTest(double d)
	{
		return d;
	}
}

Compile the project and get the Fntest.dll file.
Create a new Microsoft Visual Basic .NET Console Application project.

Paste the following code in Module1.vb:

Module Module1

    Declare Function fnTest Lib "fnTest.dll" (ByVal d As Date) As Date

    Sub Main()
        Dim m As Date
        m = fnTest(System.DateTime.Now)
        System.Console.WriteLine(m)
    End Sub

End Module

Compile the project.
Put the fnTest.dll in the same folder as the executable (.exe) file, and then run the .exe file. You receive the exception error message.

To work around this problem, use the following code:

Module Module1

    Declare Function fnTest Lib "fnTest.dll" (ByVal d As Date) As Double

    Sub Main()
        Dim m As Double
        Dim d As Date
        m = fnTest(System.DateTime.Now)
        d = DateTime.FromOADate(m)
        System.Console.WriteLine(d)
    End Sub

End Module