Marshaling Classes, Structures, and Unions

Classes and structures are similar in the .NET Framework. Both can have fields, properties, and events. They can also have static and nonstatic methods. One notable difference is that structures are value types and classes are reference types.

The following table lists marshaling options for classes, structures, and unions; describes their usage; and provides a link to the corresponding platform invoke sample.

Type	Description	Sample
Class by value.	Passes a class with integer members as an In/Out parameter, like the managed case.	SysTime
Structure by value.	Passes structures as In parameters.	Structs
Structure by reference.	Passes structures as In/Out parameters.	OSInfo
Structure with nested structures (flattened).	Passes a class that represents a structure with nested structures in the unmanaged function. The structure is flattened to one big structure in the managed prototype.	FindFile
Structure with nested structures (not flattened).	Passes a structure with an embedded structure.	Structs
Structure with a pointer to another structure.	Passes a structure that contains a pointer to a second structure as a member.	Structs
Array of structures with integers by value.	Passes an array of structures that contain only integers as an In/Out parameter. Members of the array can be changed.	Arrays
Array of structures with integers and strings by reference.	Passes an array of structures that contain integers and strings as an Out parameter. The called function allocates memory for the array.	OutArrayOfStructs
Unions with value types.	Passes unions with value types (integer and double).	Unions
Unions with mixed types.	Passes unions with mixed types (integer and string).	Unions
Null values in structure.	Passes a null reference (Nothing in Visual Basic) instead of a reference to a value type.	HandleRef

See Also

Marshaling Data with Platform Invoke | Platform Invoke Data Types | Marshaling Strings | Marshaling Arrays of Types | Miscellaneous Marshaling Samples