C#调用DLL

第一个是C#程序；第二个是测试用的dll，没有头文件但已经导出了一个函数。两个代码都可以直接编译。

C# code

using System;
using System.Runtime.InteropServices;
[StructLayout(LayoutKind.Sequential)]
struct NSP
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
public string serverAddress;
public Int16 numLicAvail;
}
class Program
{
[DllImport("MyDll.dll")]
static extern int EnumServer(
byte[] nsps,              // <--- just marshaled as byte array
        ref int size);
static void Main(string[] args)
{
int sizeArray = 4;
int sizeNSP = Marshal.SizeOf(typeof(NSP));
//
// allocate storage and PInvoke
//
        byte[] buf = new byte[4 * sizeNSP];
int result = EnumServer(buf, ref sizeArray);
//
// get results, using Marshal class to unpack
//
        GCHandle pinned = GCHandle.Alloc(buf, GCHandleType.Pinned);
for(int i=0; i<sizeArray; i++)
{
IntPtr ptr = new IntPtr(pinned.AddrOfPinnedObject().ToInt64() + i * sizeNSP);
NSP nsp = (NSP) Marshal.PtrToStructure(ptr, typeof(NSP));
Console.WriteLine(nsp.serverAddress + ": " + nsp.numLicAvail);
}
pinned.Free();
Console.ReadLine();
}
}

C/C++ code

// MyDll.cpp
//
#include <windows.h>
typedef struct tag_nsproServerInfo{
char   serverAddress[32];
short  numLicAvail;
}NSP;
extern "C"
{
__declspec(dllexport) int EnumServer(NSP* pNSP, int* size)
{
strcpy(pNSP[0].serverAddress, "hello");
pNSP[0].numLicAvail = 888;
strcpy(pNSP[1].serverAddress, "world");
pNSP[1].numLicAvail = 999;
*size = 2;
return 1234;
}
}