C#調用C++類庫的幾種方式

1、  直接調用C++類庫中的公共方法

使用DllImport特性對方法進行調用，比如一個C++類庫SampleCppWrapper.dll中的公共方法：

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

__stdcall表示調用約定：參數都是從右向左通過堆棧傳遞， 函數調用在返回前要由被調用者清理堆棧。

在C#中，調用如下：

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

注意參數的類型，之后，可直接在C#編程中使用這個方法。

 

2、  調用C++類庫中的類的方法

C#不能直接調用C++類庫中的類，需要一種變通的解決方式，通過再做一個C++類庫把要調用的類成員方法暴露出來，比如下面這個C++類：

SampleCppClass.h

#pragma once

class __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;
}

我們要調用SampleCppClass中的Add和Sub兩個方法，所以我們再寫一個C++類庫，通過公共方法間接調用類成員方法：

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，再調用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++類庫中的回調函數

C++的回調函數是一種事件響應機制，和C#的委托相似，比如一個C++類中的回調函數：

SampleCppClass.h

#pragma once

typedef 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);
        }
    }
}

我們通過C++再寫一個類庫進行封裝，把類中的方法暴露出來：

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#中進行調用：

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;
        }
    }
}