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

#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:

#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

#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

#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

#include "AppleWrapper.h"
#include 
 
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：

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：

#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

#include "AppleWrapper.h"
#include "apple.h"
#include 
 
#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