延續上篇(C# 使用C++ DLL檔)之後，一般使用DLL時，除了將參數提供給DLL演算法做使用，也需將演算法結果從DLL回傳回去，所以這次就來說明如何回傳結果給C#吧。
目前我了解到如果要從DLL回傳結果給C#，都會使用指標做回傳，而我先前測試經驗，C++撰寫上比較不會遇到問題，但在接收端C#有遇過接不到數值、接錯值、或是跑久還造成程式當掉，重點是DLL除錯還不怎麼容易，像是瞎子摸象的感覺，如果有人知道怎樣較快除DLL的Bug，再歡迎留言告訴我，感謝!!!經過一番的測試之後，我目前可正常回傳的資訊分別為字串與float陣列資訊。
Extern.cpp
#ifdef SYSALGORITHM_EXPORTS
#define SYSALGORITHM_API __declspec(dllexport)
#include "SysAlgorithm.h"
extern "C" SYSALGORITHM_API int add(int a, int b)
{
Calculator Calculator;
return Calculator.add(a, b);
}
extern "C" SYSALGORITHM_API int subtract(int a, int b)
{
Calculator Calculator;
return Calculator.subtract(a, b);
}
extern "C" SYSALGORITHM_API void getDLLValue(float * DLLvalue)
{
Calculator Calculator;
return Calculator.getDLLValue(DLLvalue);
}
extern "C" SYSALGORITHM_API void getDLLInfo(char * DLLInfo)
{
Calculator Calculator;
return Calculator.getDLLInfo(DLLInfo);
}
#endif
SysAlgorithm.h
#pragma once
#ifndef SYSALGORITHM_H
#define SYSALGORITHM_H
#include <fstream>
#include <string>
class Calculator
{
public:
Calculator();
~Calculator();
int add(int a, int b);
int subtract(int a, int b);
void getDLLValue(float * DLLvalue);
void getDLLInfo(char * DLLInfo);
};
#endif // !SYSALGORITHM_H
SysAlgorithm.cpp
#include "SysAlgorithm.h"
Calculator::Calculator()
{
}
Calculator::~Calculator()
{
}
int Calculator::add(int a, int b)
{
return(a + b);
}
int Calculator::subtract(int a, int b)
{
return(a - b);
}
void Calculator::getDLLValue(float * DLLvalue)
{
DLLvalue[0] = 0;
DLLvalue[1] = 1.2;
DLLvalue[2] = -1.2;
}
void Calculator::getDLLInfo(char * DLLInfo)
{
char Info[20] = "return DLLInfo";
strcpy_s(DLLInfo, strlen(Info) + 1, Info);
}
C#
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace SysUI
{
public partial class Form1 : Form
{
[DllImport("SysAlgorithm.dll", EntryPoint = "add", CallingConvention = CallingConvention.Cdecl)]
private static extern int add(int a, int b);
[DllImport("SysAlgorithm.dll", EntryPoint = "subtract", CallingConvention = CallingConvention.Cdecl)]
private static extern int subtract(int a, int b);
[DllImport("SysAlgorithm.dll", EntryPoint = "getDLLValue", CallingConvention = CallingConvention.Cdecl)]
private static extern void getDLLValue([MarshalAs(UnmanagedType.LPArray)]float[] value);
[DllImport("SysAlgorithm.dll", EntryPoint = "getDLLInfo", CallingConvention = CallingConvention.Cdecl)]
private static extern void getDLLInfo(StringBuilder DLLInfo);
private StringBuilder DLLInfo = new StringBuilder(20);
private float[] DLLvalue = new float[3];
public Form1()
{
InitializeComponent();
label1.Text = add(3, 5).ToString();
label2.Text = subtract(3, 5).ToString();
getDLLValue(DLLvalue);
getDLLInfo(DLLInfo);
label6.Text = DLLvalue[0].ToString() + "," + DLLvalue[1].ToString("F2") + "," + DLLvalue[2].ToString("F2");
label8.Text = DLLInfo.ToString();
}
}
}
為了可以正確取得從DLL演算法回傳參數，C#的DllImport這邊很重要!!記得要注意
結果圖：
