Question

In my header file I have a function pointer and a struct:

typedef struct _CONTINUE_STATE {
    DWORD CurrentCycle;
    CommandProc* CommandFunc;
    void* Resered;
} CONTINUE_STATE, *PCONTINUE_STATE;

—

typedef HRESULT (*CommandProc)(SOCKET client, char* command, char* response, CONTINUE_STATE* continueProc);

The problem is that CommandProc and CONTINUE_STATE both use each other. The function uses the struct as a argument and the struct uses the function as a member. This causes issues because whichever type is at the top of the header isn’t able to find the type it uses.

Thanks in advance.

Edit: I know I can use void* for the func type in the struct then cast it later on but I’m wondering if there’s a better way.

Answer 1

Firstly:

typedef struct _CONTINUE_STATE {
    DWORD CurrentCycle;
    CommandProc* CommandFunc;
    void* Resered;
} CONTINUE_STATE, *PCONTINUE_STATE;

No need for typedefs, and you should not typedef pointers. So lets make that:

struct _CONTINUE_STATE {
    DWORD CurrentCycle;
    CommandProc* CommandFunc;
    void* Resered;
};

Next, names begining with an underscorea and an uppercase letter are reserved, so:

struct CONTINUE_STATE {
    DWORD CurrentCycle;
    CommandProc* CommandFunc;
    void* Resered;
};

And, if you really do need mutually referenced type names, which isn’t obvious from your code, and isn’t very commonly needed then:

struct CONTINUE_STATE {
    DWORD CurrentCycle;
    struct CommandProc * CommandFunc;   // forward declaration
    void* Resered;
};

Lastly, by convention type names in C++ are in mixed case, with uppercase being reserved for constants, so:

struct ContinueState {
    DWORD CurrentCycle;
    struct CommandProc * CommandFunc;   // forward declaration
    void* Resered;
};