converting c++ API struct to c#

Question

I am trying to convert c++ api example to c#. but I can not find the way of struct pointer in struct by the way struct has string types. Here is c++ structs and functions

struct AuthParam { char server_ip[32];  char username[50];  char password[50]; };
struct CameraInfo { int index;  char devicename[100];  char smallrtsp[1000];  char bigrtsp[1000]; };
struct SingleDevice { char deviceid[50];  char devicename[100];  int  flag_onuse;  int  cameralist_size;  CameraInfo* cameralist; };
struct DeviceList { int listsize;  SingleDevice* singledevicelist; };

typedef int (WINAPI capi_init)(void);
typedef int (WINAPI capi_disabled)(void);
typedef int (WINAPI capi_GetServerTimeCode)(char* server_ip, unsigned int* timecode);
typedef int (WINAPI GetDevicelist)(AuthParam auth_para, DeviceList* devicelist);

and this is my c# code but I can not find the way of defining struct pointer in struct I got " Error CS0208 Cannot take the address of, get the size of, or declare a pointer to a managed type ('Form1.CameraInfo')" error.

public struct AuthParam
        {
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
            public string server_ip;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 50)]
            public string username;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 50)]
            public string password;
        };

        [StructLayout(LayoutKind.Sequential)]
        public struct CameraInfo
        {
            public int index;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 100)]
            public string devicename;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 1000)]
            public string smallrtsp;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 1000)]
            public string bigrtsp;
        };

        [StructLayout(LayoutKind.Sequential)]
        public struct SingleDevice
        {
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 50)]
            public string deviceid;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 100)]
            public string devicename;
            public int flag_onuse;
            public int cameralist_size;

            public CameraInfo *cameralist;
        };

        [StructLayout(LayoutKind.Sequential)]
        public unsafe struct DeviceList
        {
            public int listsize;
            public SingleDevice *singledevicelist;
        };

[DllImport("c:\\lib\\api_client.dll")] public static extern int capi_init();
        [DllImport("c:\\lib\\api_client.dll")] public static extern int capi_disabled();
        [DllImport("c:\\lib\\api_client.dll")] public static extern int capi_GetServerTimeCode(string ip, ref uint timecode);
        [DllImport("c:\\lib\\api_client.dll")] public static extern int GetDevicelist (AuthParam auth_para,ref  DeviceList devicelist);

is there any way to achieve this convertion?

Maybe that line should be public ref SingleDevice singledevice? Or you can use IntPtr for a pointer. — Arush Agarampur
– Arush Agarampur, Commented Dec 25, 2019 at 23:12

walid barakat · Accepted Answer · 2019-12-25 23:22:17Z

1

i think this error because of the different nature of c++ (un-managed code) and c# (managed code), so maybe using System.IntPtr as a pointer to your camera struct.

please consider this question here, and you can find about P/Invoke Interop Assistant which is an open source tool to convert your code from the un-managed code to a managed C# code. with a small blog article about C++/C# interoperability

answered Dec 25, 2019 at 23:22

walid barakat

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