C#调用的C++库的使用（三种方式）
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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 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：个人感觉与方法二大同小异，没有深入去探究，所以也就不太清楚功能上的优劣。
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;
}
}
}