Question

I have the following recursive type definitions in C and I am wondering how to get it to work:

typedef int (*foo) (bar *);
typedef foo *bar;

The sizes of the pointers are well known so this should be OK.

I somehow need to forward declare bar as some anonymous type that I can then typedef correctly. Not sure how to do this in C since it isn’t a struct

I want to avoid declaring foo as:

typedef int (*foo) (void *)

because then I lose some type checking properties.

Answer 1

There is no forward declaration for typedefs in C, unfortunately.

UPD.

You can create indirectly recursive type as follows:

struct bar;
typedef int (*foo)(struct bar *);

struct bar {
    foo f;
};

And then get pointer to function through the field of the argument. But this requires the structure to be allocated somewhere (may be on stack) and additional pointer dereferencing.

int boo(struct bar *bar) {
    return (bar->f)(bar); // infinite loop
}

int main(void) {
    struct bar baz = { &boo };
    return boo(&baz);
}