.NET Framework Platform Invoke Marshaling unions
Example
Value-type fields only
C++ declaration
typedef union
{
char c;
int i;
} CharOrInt;
C# declaration
[StructLayout(LayoutKind.Explicit)]
public struct CharOrInt
{
[FieldOffset(0)]
public byte c;
[FieldOffset(0)]
public int i;
}
Mixing value-type and reference fields
Overlapping a reference value with a value type one is not allowed so you cannot simply use the FieldOffset(0) text; FieldOffset(0) i;
typedef union
{
char text[128];
int i;
} TextOrInt;
and generally you would have to employ custom marshaling. However, in particular cases like this simpler technics may be used:
[StructLayout(LayoutKind.Sequential)]
public struct TextOrInt
{
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 128)]
public byte[] text;
public int i { get { return BitConverter.ToInt32(text, 0); } }
}
