Structs can be passed and returned by value, or by reference.
If a parameter is declared with a struct type, the parameter is passed by value. To pass a struct by reference, declare a parameter with a pointer to struct type.
C functions returning structs If a C function is declared as returning a struct type, the struct is returned by value, and wrapped in an instance of the correct struct class automatically. If a C function is declared as returning a pointer to a struct, it will return an alien instance. This is because there is no way to distinguish between a pointer to a single struct and a pointer to an array of zero or more structs. It is up to the caller to wrap it in a struct using memory>struct, or a specialized array of structs using <direct-T-array>, respectively.
An example of a struct declaration:
USING: alien.c-types classes.struct ;
STRUCT: Point
{ x int }
{ y int }
{ z int } ;
A C function which returns a struct by value:
USING: alien.syntax ;
FUNCTION: Point give_me_a_point ( c-string description )
A C function which takes a struct parameter by reference: