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 <assert.h>

int main(void)
{
    struct tagApple * pApple;
    pApple= GetInstance();
    SetColor(pApple, 1);
    int color = GetColor(pApple);
    printf("color = %d
", 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 <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