Question

struct mystruct
{
    int   i;
    double f;
} ;

typedef mystruct myotherstruct;

//the other .cpp file
struct mystruct;  //OK,this is a correct forward declaration.
struct myotherstruct; // error C2371（in vc2k8）: 'myotherstruct' : redefinition; different basic types

Hi all.
Why can’t I forward declare myotherstruct?

Answer 1

The myotherstruct identifier is not a struct tag, it is a type name in its own rights. You use it without the struct keyword. Once defined, the name cannot be reused for a struct tag. In your example, you are not forward-declaring myotherstruct type, you are forward-declaring a struct with the tag myotherstruct, which gives you an error because the name myotherstruct has already been taken for the typedef.