关于C# C++ 函数指针可以相互调用吗

问题：在C++和C#之中都有很多callback method,可以相互调用吗,怎么传递？

答案：

 1.定义c++ dll ,导出方法

    // sort.cpp : 定义 DLL 应用程序的导出函数。

    //

    #include "stdafx.h"

    #include "sort.h"

    #include "stdlib.h"

    #include "iostream"

    // 这是导出函数的一个示例。

    typedef  int (__cdecl *compare )(const void *elem1, const void *elem2 ) ;

    void fnsort(int arr[],int size,compare fuccsharp)

    {

    std::cout<<"\r\narray length:"<<size<<"\r\n";

    std::cout << "entry fnsort in cpp\r\n";

    for(int index=0; index<size;index++){

    std::cout << arr[index] << " ";

    }

    qsort(arr,size,sizeof(int),fuccsharp);

    std::cout<<"\r\n sort end\r\n";

    for(int index=0; index<size;index++){

    std::cout << arr[index] << " ";

    }

    return ;

    }

    定义导出文件sort.def

    LIBRARY  BTREE

    EXPORTS

    fnsort

    现在我们期待c#能呼叫fnsort,并实现funccsharp来实现排序算法,在c#中LoadLibrary,GetProcAddress,FreeLibrary当然是必不可少的.另外定义接口实现compare ,传入两个const void *,传出int

    static int SortASC(IntPtr a, IntPtr b) {

    int va = System.Runtime.InteropServices.Marshal.ReadInt32(a);

    int vb = System.Runtime.InteropServices.Marshal.ReadInt32(b);

    return va - vb;

    }

    static int SortDESC(IntPtr a, IntPtr b)

    {

    int va = System.Runtime.InteropServices.Marshal.ReadInt32(a);

    int vb = System.Runtime.InteropServices.Marshal.ReadInt32(b);

    return vb - va;

    }

    同时定义委托

    [UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]

    public delegate int INTARRAYSORT(IntPtr a, IntPtr b);

    现在我们认为我们实现了int (__cdecl *compare )(const void *elem1, const void *elem2 ) ;现在没事了,一切顺利了,Marshal.GetDelegateForFunctionPointer会将一个intptr转换为一个委托 ,new delegate(pfunc)可以将一个csharp func转换为一个函数指针传绘cpp,依上例,完整实现

    using System;

    using System.Text;

    using System.Runtime.InteropServices;

    namespace callDLL

    {

    class Program

    {

    [DllImport("kernel32")]

    public static extern IntPtr LoadLibrary(string lpFileName);

    [DllImport("Kernel32")]

    public static extern bool FreeLibrary(IntPtr handle);

    [DllImport("Kernel32")]

    public static extern IntPtr GetProcAddress(IntPtr handle, String funcname);

    [UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]

    public delegate int INTARRAYSORT(IntPtr a, IntPtr b);

    [UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]

    public delegate void CPPSORT(int[] arr, int size, INTARRAYSORT callback);

    static int SortASC(IntPtr a, IntPtr b) {

    int va = System.Runtime.InteropServices.Marshal.ReadInt32(a);

    int vb = System.Runtime.InteropServices.Marshal.ReadInt32(b);

    return va - vb;

    }

    static int SortDESC(IntPtr a, IntPtr b)

    {

    int va = System.Runtime.InteropServices.Marshal.ReadInt32(a);

    int vb = System.Runtime.InteropServices.Marshal.ReadInt32(b);

    return vb - va;

    }

    static void Main(string[] args)

    {

    IntPtr dll = LoadLibrary("sort.dll");

    IntPtr func=GetProcAddress(dll, "fnsort");

    CPPSORT cppsort = (CPPSORT)Marshal.GetDelegateForFunctionPointer(func, typeof(CPPSORT));

    int[] arr = new int[] { 1, 7, 4 };

    //回叫函数可以使用委托实现

    cppsort(arr,arr.Length,new INTARRAYSORT(SortASC));

    cppsort(arr, arr.Length, new INTARRAYSORT(SortDESC));

    FreeLibrary(dll);

    Console.WriteLine("\r\nend");

    Console.Read();

    }

    }

    }

    输出如下

    array length:3

    entry fnsort in cpp

    1 7 4

    sort end

    1 4 7

    array length:3

    entry fnsort in cpp

    1 4 7

    sort end

    7 4 1

    end

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