如何用C语言封装 C++的类，在 C里面使用

本文给出了一种方法。基本思想是，写一个 wrapper文件，把 C++类封装起来，对外只提供C语言的接口，和 C++i相关的都在 wrapper的实现文件里实现。

1. apple.h

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#ifndef __APPLE_H__

#define __APPLE_H__

class Apple

{

public:

enum

{

APPLE_COLOR_RED,

APPLE_COLOR_BLUE,

APPLE_COLOR_GREEN,

};

Apple();

int GetColor(void);

void SetColor(int color);

private:

int m_nColor;

};

#endif

apple.cpp:

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#include "apple.h"

Apple::Apple():m_nColor(APPLE_COLOR_RED)

{

}

void Apple::SetColor(int color)

{

m_nColor = color;

}

int Apple::GetColor(void)

{

return m_nColor;

}

2. AppleWrapper.h

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#ifndef _APPLE_WRAPPER_H__

#define _APPLE_WRAPPER_H_

struct tagApple;

#ifdef __cplusplus

extern "C" {

#endif

struct tagApple *GetInstance(void);

void ReleaseInstance(struct tagApple **ppInstance);

extern void SetColor(struct tagApple *pApple, int color);

extern int GetColor(struct tagApple *pApple);

#ifdef __cplusplus

};

#endif

#endif

AppleWrapper.cpp

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#include "AppleWrapper.h"

#include "apple.h"

#ifdef __cplusplus

extern "C" {

#endif

struct tagApple

{

Apple apple;

};

struct tagApple *GetInstance(void)

{

return new struct tagApple;

}

void ReleaseInstance(struct tagApple **ppInstance)

{

delete *ppInstance;

*ppInstance = 0;

}

void SetColor(struct tagApple *pApple, int color)

{

pApple->apple.SetColor(color);

}

int GetColor(struct tagApple *pApple)

{

return pApple->apple.GetColor();

}

#ifdef __cplusplus

};

#endif

3. test.c

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#include "AppleWrapper.h"

#include <assert.h>

int main(void)

{

struct tagApple * pApple;

pApple= GetInstance();

SetColor(pApple, 1);

int color = GetColor(pApple);

printf("color = %d\n", color);

ReleaseInstance(&pApple);

assert(pApple == 0);

return 0;

}

可以用 GCC编译：

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g++ -c apple.cpp

g++ -c apple.cpp AppleWrapper.cpp

gcc test.c -o test AppleWrapper.o apple.o -lstdc++

其实， wrapper里的 struct 完全可以不要，定义一个 handle更好：

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#ifndef _APPLE_WRAPPER_H__

#define _APPLE_WRAPPER_H_

#ifdef __cplusplus

extern "C" {

#endif

int GetInstance(int *handle);

void ReleaseInstance(int *handle);

extern void SetColor(int handle, int color);

extern int GetColor(int handle);

#ifdef __cplusplus

};

#endif

#endif

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#include "AppleWrapper.h"

#include "apple.h"

#include <vector>

#ifdef __cplusplus

extern "C" {

#endif

static std::vector<Apple *> g_appleVector;

int GetInstance(int * handle)

{

g_appleVector[0] = new Apple;

*handle = 0;

return 1;

}

void ReleaseInstance(int *handle)

{

delete g_appleVector[*handle];

*handle = -1;

}

void SetColor(int handle, int color)

{

g_appleVector[handle]->SetColor(color);

}

int GetColor(int handle)

{

return g_appleVector[handle]->GetColor();

}

#ifdef __cplusplus

};

#endif