Default Marshaling for Characters 

When a managed Char type, which has Unicode formatting by default, is passed to unmanaged code, the interop marshaler converts the character set to ANSI. You can apply the DllImportAttribute attribute to platform invoke declarations and the StructLayoutAttribute attribute to a COM interop declaration to control which character set a marshaled Char type uses.

See Also

Concepts

Blittable and Non-Blittable Types
Directional Attributes
Copying and Pinning
Specifying a Character Set

Other Resources

Default Marshaling Behavior