项目要用到C#调用C++代码，折腾了好久，终于搞定了。总结一下。
问题的复杂性在于C++是非托管代码(unmanaged/native code)，C#是托管代码(managed code)，不可直接调用。这里先讲一下C#调用C++中的函数。这个相对简单一些，网上现成的代码也比较多，这里的就是转自http://tech.ddvip.com/2009-03/1236764166111066_1.html的方法。
有两种方法：静态调用和动态调用。
静态调用
假设有C++代码nativeCPP.cpp：
1 extern "C" __declspec(dllexport) int add(int x, int y)
2 {
3 return x + y;
4 }
5
编译生成nativeCPP.dll，将其放在C#工程的bin目录下。C#代码如下：
1 using System;
2 using System.Collections.Generic;
3 using System.Text;
4 using System.Runtime.InteropServices; //一定要有
5
6 namespace InteropDemo
7 {
8 class Program
9 {
10 [DllImport("nativeCPP.dll", EntryPoint = "add", ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
11 public static extern int add(int a, int b); //正常声明即可
12 static void Main(string[] args)
13 {
14 Console.WriteLine(add(1, 2));
15 Console.Read();
16 }
17 }
18 }
19
动态调用
1 using System;
2 using System.Collections.Generic;
3 using System.Text;
4 using System.Runtime.InteropServices; //一定要有
5
6 namespace InteropDemo
7 {
8 class Program
9 {
10 [DllImport("nativeCPP.dll", EntryPoint = "add", ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
11 public static extern int add(int a, int b); //正常声明即可
12 static void Main(string[] args)
13 {
14 Console.WriteLine(add(1, 2));
15 Console.Read();
16 }
17 }
18 }
19
1 using System;
2 using System.Collections.Generic;
3 using System.Text;
4 using System.Runtime.InteropServices;
5
6 namespace InteropDemo
7 {
8 //封装kernel32中的几个方法（虽然我觉得没什么必要）
9 public static class NativeMethod
10 {
11 [DllImport("kernel32.dll", EntryPoint = "LoadLibrary")]
12 public static extern int LoadLibrary(
13 [MarshalAs(UnmanagedType.LPStr)] string lpLibFileName);
14
15 [DllImport("kernel32.dll", EntryPoint = "GetProcAddress")]
16 public static extern IntPtr GetProcAddress(int hModule,
17 [MarshalAs(UnmanagedType.LPStr)] string lpProcName);
18
19 [DllImport("kernel32.dll", EntryPoint = "FreeLibrary")]
20 public static extern bool FreeLibrary(int hModule);
21 }22 class Program
23 {
24 static void Main(string[] args)
25 {
26 //1. 动态加载C++ Dll
27 int hModule = NativeMethod.LoadLibrary(@"c:nativeCPP.dll");
28 if (hModule == 0) return;
29
30 //2. 读取函数指针
31 IntPtr intPtr = NativeMethod.GetProcAddress(hModule, "Add");
32
33 //3. 将函数指针封装成委托
34 Add addFunction = (Add)Marshal.GetDelegateForFunctionPointer(intPtr, typeof(Add));
35
36 //4. 测试
37 Console.WriteLine(addFunction(1, 2));
38 Console.Read();
39 }
40
41 /// <summary>
42 /// 函数指针
43 /// </summary>
44 /// <param name="a"></param>
45 /// <param name="b"></param>
46 /// <returns></returns>
47 delegate int Add(int a, int b);
48
49 }
50
51 }
我不懂动态调用与静态调用的原理，只知道从表相来看，静态调用C++的dll必须放在C#工程目录bin下，而动态的话只要在C#中指定路径即可。
