How to arrange C structure / function declarations that use each other?

Question

I am trying to create a structure called "IExampleVtbl" that will contain a pointer to my functions (SetStringPtr, GetStringPtr) and will be part of another "IExample" structure .

But I want to pass another "IExample" structure as a parameter to the functions (SetStringPtr, GetStringPtr) .

This is the code:

#include <windows.h>
#include <stdio.h>

typedef struct {
    SetStringPtr *SetString;
    GetStringPtr *GetString;
} IExampleVtbl;

typedef struct {
    IExampleVtbl *lpVtbl;
    DWORD   count;
    char    buffer[80];
} IExample;

typedef long SetStringPtr(IExample *, char *);
typedef long GetStringPtr(IExample *, char *, long);

long SetString(IExample *this, char * str)
{
    ...

    return(0);
}

long GetString(IExample *this, char *buffer, long length)
{
    ...

    return(0);
}

As you can see, the first structure must know about the functions, the functions must know about the second structure, which must know about the first structure.

How can i solve this?

Answer 1

,

• typedefs
• typedefs

, :

typedef struct IExampleVtblTag IExampleVtbl;
typedef struct IExampleTag IExample;
typedef long SetStringPtr(IExample *, char *);
typedef long GetStringPtr(IExample *, char *, long);

struct IExampleVtblTag {
    SetStringPtr *SetString;
    GetStringPtr *GetString;
};

struct IExampleTag {
    IExampleVtbl *lpVtbl;
    DWORD   count;
    char    buffer[80];
};

long SetString(IExample *this, char * str)
{
    return(0);
}

long GetString(IExample *this, char *buffer, long length)
{
    return(0);
}

Answer 2

alias:

// Forward declaration of the structure IExample
// And at the same time definition of the type-alias IExample
typedef struct IExample IExample;

typedef long SetStringPtr(IExample *, char *);
typedef long GetStringPtr(IExample *, char *, long);

// Now the definition of the structures
typedef struct { ... } IExampleVtbl;

// Because the previous type-alias definition, we need to specify a structure tag
struct IExample { ... };

Answer 3

typedef , typedef'd, , .

typedef struct IExample IExample;

typedef long SetStringPtr(IExample *, char *);
typedef long GetStringPtr(IExample *, char *, long);

typedef struct {
    SetStringPtr *SetString;
    GetStringPtr *GetString;
} IExampleVtbl;

struct IExample {
    IExampleVtbl *lpVtbl;
    long   count;
    char    buffer[80];
};