C#封装C++DLL(特别是char*对应的string)

1、新建一个C#-Windows-类库（用于创建C#类库(.dll)的项目）类型的工程

2、对于普通C++函数

XXXX_API void cppFun(int i);

在cs代码中添加

[DllImport("c++xxxx.dll")]

public static extern void cppFun(int i);

3、对于C++中的结构体，因为C++中结构体默认访问控制为public，而C#中结构体默认为private，所以要显示指定一下

typedef struct {
　　　　 char sDVRIP[16]; /* DVR IP地址 */
　　　　 char sDVRIPMask[16]; /* DVR IP地址掩码 */
　　　　 DWORD dwNetInterface; /* 10M/100M自适应,索引 */
　　　　 WORD wDVRPort; /* 端口号 */
　　　　 BYTE byMACAddr[MACADDR_LEN]; /* 服务器的物理地址 */
　}NET_POSA_ETHERNET;

C#对应

public struct NET_POSA_ETHERNET
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)]
public string sDVRIP; //DVR IP地址
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)]
public string sDVRIPMask; // DVR IP地址掩码
public uint dwNetInterface; //网络接口 1-10MBase-T 2-10MBase-T全双工 3-100MBase-TX 4-100M全双工 5-10M/100M自适应
public uint wDVRPort; //端口号
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 6)]
public byte[] byMACAddr; //[MACADDR_LEN]; //PPPoE用户名//服务器的物理地址
}

将string转为IntPtr：IntPtr System.Runtime.InteropServices.Marshal.StringToCoTaskMemAuto(string)

将IntPtr转为string：string System.Runtime.InteropServices.MarshalPtrToStringAuto(IntPtr)

类型对照：

BSTR ---------  StringBuilder

LPCTSTR --------- StringBuilder

LPCWSTR ---------  IntPtr

handle---------IntPtr

hwnd-----------IntPtr

char *----------string

int * -----------ref int

int &-----------ref int

void *----------IntPtr

unsigned char *-----ref byte

Struct需要在C#里重新定义一个Struct

CallBack回调函数需要封装在一个委托里

typedef void(* CallbackResult)(int progress, char *result);
extern"C" _declspec(dllexport)
void subscribe0(char* eventName, CallbackResult callback)
{
    callback(8, "AAABBB");
}

C#
public delegate void CallBack(int progress, string lParam);
[DllImport("deepstream_for_csharp")]
public static extern void subscribe0(string eventName, CallBack func);
CallBack myCallBack = new CallBack(ReportView);
subscribe0("adsm", myCallBack);
public static void ReportView(int progress, string lParam)
    {
        Debug.Log("AAAAAA");
    }

C++:
EXPORTS_U3DDLL
void subscribe(char* eventName,void(*func)(const char*))
{
    if (client == 0)
    {
        std::cout << "client has not been created!!";
        return;
    }
    const deepstream::SubscriptionId event_sub_id =
        client->event.subscribeForUnity(eventName, func);
    subEventID[eventName] = event_sub_id;
}

SubscriptionId subscribeForUnity(const std::string &name, std::function<void(const char* data)> callback)
{
Buffer name_buff(name);
Event::SubscribeFn core_callback([callback, this](const Buffer &prefixed_buff) {
const json &data = type_serializer_.prefixed_to_json(prefixed_buff);
const std::string &data_string(data);
callback(data_string.c_str());
});
SubscriptionId subscription_id = client_.event.subscribe(name_buff, core_callback);
return subscription_id;
}

C#:
[DllImport("deepstream_for_csharp")]
public static extern void subscribe(string eventName, SubscribeCallBack callback);
public delegate void SubscribeCallBack(string data);
public static void eventPosCallBack(string data)
{
    Debug.Log("pos:" + data+data.Length);
}
subscribe("pos", new SubscribeCallBack(eventPosCallBack));