Hello,

I'm having the following problem and I need some help from you:

I've a dll writen in C that has one function that has a parameter that's an
array  of structures of type T_MyStruct.

The structure T_MyStruct has just one field, being an array of 7 stuctures
of type T_A.

The structure T_A has 2 fields. One is an integer and the other one is a
union of structures (T_StructUnion).

The union T_StructUnion is composed by 2 structures: structure T_B and
structure T_C.

Booth structures, T_B and T_C, have one field that is a byte array of size 50.

I declared it in C# as follows:

[StructLayout(LayoutKind.Sequential)]
public struct T_B{

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 100)]
    byte[] fieldB1;
}

[StructLayout(LayoutKind.Sequential)]
public struct T_C{

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 100)]
    byte[] fieldC1;

}

[StructLayout(LayoutKind.Explicit)]
public struct T_StructUnion{

    [System.Runtime.InteropServices.FieldOffset(0)]
    public T_B fieldUnion1;

    [System.Runtime.InteropServices.FieldOffset(0)]
    public T_C fieldUnion2;
}

[StructLayout(LayoutKind.Sequential)]
public struct T_A{

    public int fieldA1;

    public StructUnion fieldA2;
}

[StructLayout(LayoutKind.Sequential)]
public T_MyStruct{

    [MarshalAs(UnmanagedType.ByValArray,SizeConst = 7)]
    public T_A[] myField;
}

[DllImport("mylib.dll", EntryPoint = "MyMethod", SetLastError = true)]
public static extern int MyMethod([In,Out] T_MyStruct[] myStructures);

The declaration in C languag is equivalent. The only difference is that the
fields of structures T_B and T_C are char[100], but I declared
them as byte[] in C#. The problem is not coming from this because i've other
structures defined like this and working good.

The problem is that when I invoke the method I've this error written in the
console:
"Cannot marshal field 'myField' of type 'T_MyStruct': There is no marshaling
support for this type.
Failing when marshaling from C# to C.

But if I declare the field in structure T_B and T_C as integers the error
disapears, failing then internally in the DLL because the
types are not correct.

Can someone waste some time helping me?
This is very imporant to me and I don't know why it's not working.