C# C++ 傳遞函數指針

C#和c++之間相互傳遞函數指針

在C++和C#之中都有很多callback method,可以相互調用嗎,怎麼傳遞,是我表弟的問題.

1.定義c++ dll ,導出方法

// sort.cpp : 定義 DLL 應用程序的導出函數。

//

#include "stdafx.h"
#include "sort.h"
#include "stdlib.h"
#include "iostream"
// 這是導出函數的一個示例。
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 ;
}

定義導出文件sort.def

LIBRARY  BTREE

EXPORTS
  fnsort

現在我們期待c#能呼叫fnsort,並實現funccsharp來實現排序算法,在c#中LoadLibrary,GetProcAddress,FreeLibrary當然是必不可少的.另外定義接口實現compare ,傳入兩個const void *,傳出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;
}

同時定義委托

[UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]
public delegate int INTARRAYSORT(IntPtr a, IntPtr b);

現在我們認為我們實現了int (__cdecl *compare )(const void *elem1, const void *elem2 ) ;現在沒事了,一切順利了,Marshal.GetDelegateForFunctionPointer會將一個intptr轉換為一個委托 ,new delegate(pfunc)可以將一個csharp func轉換為一個函數指針傳繪cpp,依上例,完整實現

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 };
            //回叫函數可以使用委托實現
            cppsort(arr,arr.Length,new INTARRAYSORT(SortASC));
            cppsort(arr, arr.Length, new INTARRAYSORT(SortDESC));
            FreeLibrary(dll);
            Console.WriteLine("\r\nend");
            Console.Read();
        }
    }
}

輸出如下

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 

相關閱讀：C++中使用模板傳遞函數類型 http://www.linuxidc.com/Linux/2012-11/73809.htm