Combining C ++ links in C API

Question

I have a header file for what needs to be combined with C ++ and C API. Part C is wrapped in extern "C" , but the declarations themselves are very different from C; eg:

 foo::Bar& Foo_Baz_GetBarOfQux(void *_self, const foo::Qux &qux); 

Is there a way to use it in plain C form? I obviously can't use this header, but maybe I can redo it somehow:

 /* type? */ Foo_Baz_GetBarOfQux(void*, const /* type? */); 

What puzzles me is how to declare the types of these links (if possible).

PS I know that I can write my own C-shell on top of this: I declare classes as opaque structures:

 typedef struct foo_bar foo_bar_t; typedef struct foo_baz foo_baz_t; typedef struct foo_qux foo_qux_t; 

and then write a C-like function that wraps the above function:

 extern "C" foo_bar_t* foo_baz_get_bar_of_qux( foo_baz_t* baz, foo_qux_t* qux) { return (foo_bar_t*) Foo_Baz_GetBarOfQux(baz, *(foo::Qux*)qux); } 

But I am wondering if I can directly use the original Foo_Baz_GetBarOfQux() .

Answer 1

No, you cannot directly use Foo_Baz_GetBar() , calls to a member function in c++ implicitly pass the this pointer, which does not exist in your c code.

Answer 2

In general, it would be better to use opaque structures.

In the "C" interface of the code, never try to look inside an opaque structure, just dutifully pass pointers.

In the "C ++" part, you should define the structure and actually fill it accordingly (I would avoid blind type casting).

Of course, the “C ++” part should not appear in the “C” header so that it does not confuse the C compiler.