一个基本的C问题，循环依赖中的声明 [英] A Basic C question, declarations in cyclic dependency

问题描述

我在纯C中执行 COM [

I was doing COM in plain C[^] tutorial. I have the following header file:

#ifndef EXAMPLE_H
#define EXAMPLE_H

#define BUF_SIZE 80

typedef long SetStrPtr(IExample *, char *);
typedef long GetStrPtr(IExample *, char *, long);

typedef struct {
    SetStrPtr * SetString;
    GetStrPtr * GetString;
} IExampleVtbl;

typedef struct {
    IExampleVtbl * lpVtbl;
    DWORD          count;
    char           buffer[BUF_SIZE];
} IExample;
#endif

现在，这给了我一个编译错误.因为..

1.声明结构IExample，我需要先声明IExampleVtbl
2. ..需要声明SetStrPtr和GetStrPtr
3. ..需要声明IExample

如您所见，这是一个循环依赖性.

Now this gives me a compile error. Because..

1. to declare the structure IExample, I need to first declare IExampleVtbl
2. ..which needs the declaration of SetStrPtr and GetStrPtr
3. ..which needs the declaration of IExample

Now as you can see, it''s a cyclic dependency. How to get through this?

推荐答案

尝试一下:

try this:

#ifndef EXAMPLE_H
#define EXAMPLE_H
 
#define BUF_SIZE 80

struct _IExample;
typedef struct _IExample IExample;

typedef long SetStrPtr(IExample *, char *);
typedef long GetStrPtr(IExample *, char *, long);

 
typedef struct {
    SetStrPtr * SetString;
    GetStrPtr * GetString;
} IExampleVtbl;
 
struct _IExample{
    IExampleVtbl * lpVtbl;
    DWORD          count;
    char           buffer[BUF_SIZE];
};

#endif

这很讨厌，但是唯一的方法是更改​​IExample指针使指针无效:

It''s nasty, but the only way to do it is you change the IExample pointers to void pointers:

typedef long SetStrPtr(void *, char *);
typedef long GetStrPtr(void *, char *, long);

因为所有指针的长度都是相同的，所以它会完美地工作，但是不会被强类型化.

It will work perfectly happily because all pointers are the same length, but it won''t be strongly typed.

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