Question

I have a DLL and its header file, which were written in Visual C++. I need to use the following function in a C# project:

LIBSPEC int
CprFindDevices(
  PCprDeviceInfo *ppDevInfo,
  int *pNumDevices,
  DWORD timeout
  );

I am able to import it with a DllImport, but I cannot figure out how to implement the following structure in C#:

typedef struct _CprDeviceInfo
{
  unsigned char id[ID_LEN];
  unsigned char macAddr[MAC_LEN];
  in_addr       inAddr;
  char          ipAddr[IP_LEN];
  char          devName[INFO_NAME_LEN];
  char          port1Name[INFO_NAME_LEN];
  char          port2Name[INFO_NAME_LEN];
  int           tcpPort1;
  int           tcpPort2;
  char          interfaceIpAddr[IP_LEN];
} CprDeviceInfo, *PCprDeviceInfo;

The all-upper-case variables are all known constants which I can use in my C# project.

I know I must use [StructLayout(LayoutKind.Sequential)], but am not sure what the equivalent types are for each of the structure’s members, and what the function signature would be when I import it. It’s been a while since my C++ days.

Answer 1

This should do the job for you:

struct CprDeviceInfo
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = ID_LEN)]
    string id;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = MAC_LEN)]
    string macAddr;
    uint inAddr;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = IP_LEN)]
    string ipAddr;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = INFO_NAME_LEN)]
    string devName;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = INFO_NAME_LEN)]
    string port1Name;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = INFO_NAME_LEN)]
    string port2Name;
    int tcpPort1;
    int tcpPort2;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = IP_LEN)]
    string interfaceIpAddr;
}

Make sure you are using Charset.ASCII in your DLLImport which is the default.