C# DLLImport C++ dll 几点注意事项

这两天工作当中需要用到c++写的DLL文件，使用过程当中遇到些注意事项，记录下来

1 ：正常情况下C++写好的文件当中有.dll,.lib,.h,.exp   用VS 打开.h c++头文件以后会看到DLL文件当中提供的function 如下所示

int __cdecl verifyTransResponse(char MerId[15], char OrdId[16], char TransAmt[12], char CuryId[3], char TransDate[8], char TransType[4], char OrdStat[4], char ChkValue[256]);
int __cdecl verifySignData(char *SignData, char ChkValue[256]);
int __cdecl signOrder(char MerId[15], char OrdId[16], char TransAmt[12], char CuryId[3], char TransDate[8], char TransType[4], char ChkValue[256]);
int __cdecl signData(char MerId[15], char *SignData, char ChkValue[256]);
void __cdecl setMerKeyFile(char keyFile[256]);
void __cdecl unsetMerKeyFile();
void __cdecl setPubKeyFile(char keyFile[256]);
void __cdecl unsetPubKeyFile();
int __cdecl digitalSign(char *MerId, char *SignData, char *keyFile, char *ChkValue)
int __cdecl validateSign(char *MerId, char *PlainData, char *ChkValue, char *keyFile);

2 : 新建C# 项目，将 C++ DLL文件放到BIN目录下边，如果用DLLImport方法会按照先BIN目录，然后系统文件夹顺序找DLL文件，当然也可自己放置到指定文件夹，然后DLLImport的时候指文件所在路径也可以,如c:\test.DLL,在DLLImport的时候写上该路径即可，如[DllImport("c:\test.DLL")]

3 : C#使用DLL文件示例如下

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.Web;
using System.IO;
using System.Net;
using System.Collections;
using System.Configuration;
using System.Data;


namespace zyc.NetPay
{
    public class NetPay
    {
        [DllImport("netpay.dll", EntryPoint = "?digitalSign@@YGHQADPAD00@Z")]
        public static extern int digitalSign(string MerId, string SignData, string keyFile, StringBuilder chkValue);

        [DllImport("netpay.dll", EntryPoint = "?validateSign@@YGHQADPAD00@Z")]
        public static extern int validateSign(string MerId, string PlainData, StringBuilder chkValue, string keyFile);
       
              public int GetSign(string MerId, string SignData, string keyFile, ref StringBuilder ChkValue)
        { 
           
            //string Result = "";
            ////  digitalSign
            //string pa1 = "123";
            //string pa2 = "123";
            //string pa3 = "123";
            //string pa4 = "123";
            //Byte[] chkValue = null;
            //chkValue = new Byte[100];
            //chkValue = System.Text.Encoding.Default.GetBytes("808080290000001");
            //  string i = digitalSign(pa1, pa1, pa1, pa1);
            int returValue = digitalSign(MerId, SignData, keyFile, ChkValue);
            return returValue; 
        }

            public int GetValidateSign(string MerId, string PlainData,ref StringBuilder chkValue, string keyFile)
        {
            int Result = validateSign(MerId, PlainData, chkValue, keyFile);
            return Result;
        }


    
    }
}

4 : 注意事项

   4.1 必须引用 System.Runtime.InteropServices 命名空间

   4.2  [DllImport("netpay.dll", EntryPoint = "?digitalSign@@YGHQADPAD00@Z")]

        public static extern int digitalSign(string MerId, string SignData, string keyFile, StringBuilder chkValue);

        原先C++ DLL文件当中方法名是 digitalSign ，之前我用这个方法，程序会提示找不到入口点的错误，后来在以前同事肖艳杰的帮助下找到了问题，用dependercy walker软件打开DLL文件以后看到的方法名变成了?digitalSign@@YGHQADPAD00@Z

   所以EntryPoint属性写成这样，他表示要调用C++的哪个方法

 4.3 ：关于传递参数问题，有时候C++ DLL方法当中是指针参数，且需要返回值的，类似于C#当中传址调用 这时候可以用StringBuilderw类型传递,如

[DllImport("netpay.dll", EntryPoint = "?digitalSign@@YGHQADPAD00@Z")]

        public static extern int digitalSign(string MerId, string SignData, string keyFile, StringBuilder chkValue);这是DLLImport部份

C#中使用该方法的示例程序如下

int returValue = digitalSign(MerId, SignData, keyFile, ChkValue);

这样当在C++ DLL方法当中如果改变了ChkValue变量的值，那么原先C#当中的ChkValue值也改变了 更多的的关于参数传递部份学习自网址http://blog.csdn.net/jame_peng/archive/2009/07/28/4387906.aspx的一篇文章

    

int 类型
[DllImport(“MyDLL.dll")]
//返回个int 类型
public static extern int mySum (int a1,int b1);
//DLL中申明
extern “C” __declspec(dllexport) int WINAPI mySum(int a2,int b2)
{
//a2 b2不能改变a1 b1
//a2=..
//b2=...
return a+b;
}

//参数传递int 类型
public static extern int mySum (ref int a1,ref int b1);
//DLL中申明
extern “C” __declspec(dllexport) int WINAPI mySum(int *a2,int *b2)
{
//可以改变 a1, b1
*a2=...
*b2=...
return a+b;
}


DLL 需传入char *类型
[DllImport(“MyDLL.dll")]
//传入值
public static extern int mySum (string astr1,string bstr1);
//DLL中申明
extern “C” __declspec(dllexport) int WINAPI mySum(char * astr2,char * bstr2)
{
//改变astr2 bstr 2 ，astr1 bstr1不会被改变
return a+b;
}


DLL 需传出char *类型
[DllImport(“MyDLL.dll")]
// 传出值
public static extern int mySum (StringBuilder abuf, StringBuilder bbuf );
//DLL中申明
extern “C” __declspec(dllexport) int WINAPI mySum(char * astr,char * bstr)
{
//传出char *　改变astr　bstr -->abuf, bbuf可以被改变
return a+b;
}