C#调用C++类库的几种方式

1、  直接调用C++类库中的公共方法

使用DllImport特性对方法进行调用，比如一个C++类库SampleCppWrapper.dll中的公共方法：

extern "C" __declspec(dllexport) int __stdcall Add(int n1, int n2);

__stdcall表示调用约定：参数都是从右向左通过堆栈传递， 函数调用在返回前要由被调用者清理堆栈。

在C#中，调用如下：

[DllImport("SampleCppWrapper.dll")]private static extern int Add(int n1, int n2);

注意参数的类型，之后，可直接在C#编程中使用这个方法。

 

2、  调用C++类库中的类的方法

C#不能直接调用C++类库中的类，需要一种变通的解决方式，通过再做一个C++类库把要调用的类成员方法暴露出来，比如下面这个C++类：

SampleCppClass.h

#pragma onceclass __declspec(dllexport) SampleCppClass{public:    SampleCppClass(void);    ~SampleCppClass(void);        int Add(int n1, int n2);    int Sub(int n1, int n2);};

SampleCppClass.cpp

#include "SampleCppClass.h"SampleCppClass::SampleCppClass(void){}SampleCppClass::~SampleCppClass(void){}int SampleCppClass::Add(int n1, int n2){    return n1 + n2;}int SampleCppClass::Sub(int n1, int n2){    return n1 - n2;}

我们要调用SampleCppClass中的Add和Sub两个方法，所以我们再写一个C++类库，通过公共方法间接调用类成员方法：

SampleCppWrapper.h

#pragma once#include "..\SampleCppClass\SampleCppClass.h"namespace SampleCppWrapper{    extern "C" __declspec(dllexport) int __stdcall Add(int n1, int n2);    extern "C" __declspec(dllexport) int __stdcall Sub(int n1, int n2);}

SampleCppWrapper.cpp

#include "SampleCppWrapper.h"namespace SampleCppWrapper{    SampleCppClass* g_pObj = new SampleCppClass();    int __stdcall Add(int n1, int n2)    {        return g_pObj->Add(n1, n2);    }    int __stdcall Sub(int n1, int n2)    {        return g_pObj->Sub(n1, n2);    }}

在C#中，再调用SampleCppWrapper.dll中的公共方法：

[DllImport("SampleCppWrapper.dll")]private static extern int Add(int n1, int n2);[DllImport("SampleCppWrapper.dll")]private static extern int Sub(int n1, int n2);

3、  使用C++类库中的回调函数

C++的回调函数是一种事件响应机制，和C#的委托相似，比如一个C++类中的回调函数：

SampleCppClass.h

#pragma oncetypedef void (*LoopCallback)(void* pContext);class __declspec(dllexport) SampleCppClass{public:    SampleCppClass(void);    ~SampleCppClass(void);        void SetCallbackFunc(LoopCallback callback);    void SetCallbackContext(void* pContext);    void Loop();private:    LoopCallback m_callback;    void* m_pContext;};

SampleCppClass.cpp

#include "SampleCppClass.h"SampleCppClass::SampleCppClass(void){}SampleCppClass::~SampleCppClass(void){}void SampleCppClass::SetCallbackFunc(LoopCallback callback){    m_callback = callback;}void SampleCppClass::SetCallbackContext(void* pContext){    m_pContext = pContext;}void SampleCppClass::Loop(){    for (int i=0; i<10; i++)    {        if (m_callback != NULL)        {            m_callback(m_pContext);        }    }}

我们通过C++再写一个类库进行封装，把类中的方法暴露出来：

SampleCppWrapper.h

#pragma once#include "..\SampleCppClass\SampleCppClass.h"namespace SampleCppWrapper{    typedef void (__stdcall *LoopCallbackWrapper)(void* pContext);    extern "C" __declspec(dllexport) void __stdcall SetCallbackFunc(LoopCallbackWrapper callback);    extern "C" __declspec(dllexport) void __stdcall SetCallbackContext(void* pContext);    extern "C" __declspec(dllexport) void __stdcall Loop();}

SampleCppWrapper.cpp

#include "SampleCppWrapper.h"namespace SampleCppWrapper{    LoopCallbackWrapper g_callbackWrapper;    SampleCppClass* g_pObj = new SampleCppClass();    void LoopCallbackFunc(void* pContext);    void __stdcall SetCallbackFunc(LoopCallbackWrapper callback)    {        g_callbackWrapper = callback;        g_pObj->SetCallbackFunc(LoopCallbackFunc);    }    void __stdcall SetCallbackContext(void* pContext)    {            g_pObj->SetCallbackContext(pContext);    }    void __stdcall Loop()    {        g_pObj->Loop();    }    void LoopCallbackFunc(void* pContext)    {        if (g_callbackWrapper != NULL)        {            g_callbackWrapper(pContext);        }    }}

然后，在C#中进行调用：

using System;using System.Runtime.InteropServices;using System.Windows.Forms;namespace SampleCsTest{    public partial class Form1 : Form    {        [StructLayout(LayoutKind.Sequential)]        private class Context        {            public Form1 Form { get; set; }        }        private delegate void LoopCallbackHandler(IntPtr pContext);        private static LoopCallbackHandler callback = LoopCallback;        [DllImport("SampleCppWrapper.dll")]        private static extern void SetCallbackFunc(LoopCallbackHandler callback);        [DllImport("SampleCppWrapper.dll")]        private static extern void SetCallbackContext(IntPtr pContext);        [DllImport("SampleCppWrapper.dll")]        private static extern void Loop();        private Context ctx = new Context();        public Form1()        {            InitializeComponent();        }        private void Form1_Load(object sender, EventArgs e)        {            SetCallbackFunc(callback);            ctx.Form = this;            IntPtr ptr = Marshal.AllocHGlobal(Marshal.SizeOf(ctx));            Marshal.StructureToPtr(ctx, ptr, false);            SetCallbackContext(ptr);        }        private void button1_Click(object sender, EventArgs e)        {            Loop();        }        private static void LoopCallback(IntPtr pContext)        {            Context ctx = (Context)Marshal.PtrToStructure(pContext, typeof(Context));            ctx.Form.textBox1.Text += "callback" + Environment.NewLine;        }    }}