编组结构数组的指针

Question

I am trying to invoke a driver dll for a force sensor thats been written for c/cpp. The working Cpp code looks like this:

I the header file that was delivered with the dll, the struct is defined like this

typedef struct
{
  DWORD usb_hid_idx;
  int open;
  char vid_pid[256];
  char dev_info[256];
  char sn_info[256];
  int hw_info;
  unsigned char hw_var;
  int fw_vers;
} t_DeviceInfo;

And the function I need to call is defined like this:

extern "C" DLL_API int Search(t_DeviceInfo *p_dev_info);

In the main code I just create an array of the former defined t_DeviceInfo struct and a pointer to the first element and call the function Search with this pointer:

t_DeviceInfo deviceInfo[16];
t_DeviceInfo* deviceInfoPtr = &deviceInfo[0];
int ret = search(deviceInfoPtr);

At least there, everything works fine. With C# it currently looks like this:

unsafe public struct t_DeviceInfo
{
    long usb_hid_idx;
    int open;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
    char[] vid_pid;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
    char[] dev_info;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
    char[] sn_info;
    int hw_info;
    char hw_var;
    int fw_vers;
}

unsafe public class ASTAS
{
    [DllImport("ASTAS_DLL.dll")]
    public extern static int Search(t_DeviceInfo* devInfPtr);
}

And in the main:

t_DeviceInfo[] devInfo = new t_DeviceInfo[16];

But thats about it. How do I marshal the array of structs to a fixed memory location and pass the corresponding pointer to Search() ?

Answer 1

There's no need for unsafe here. You may as well remove that. And your struct declaration is incorrect. Some of the types are wrong. An C++ DWORD is a unsigned 32 bit value. AC# long is a signed 64 bit value. A C++ unsigned char is an unsigned 8 bit value. AC# char is a 16 bit character. Typically unsigned char maps to byte .

The struct should be:

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi)]
public struct t_DeviceInfo
{
    uint usb_hid_idx;
    int open;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
    string vid_pid;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
    string dev_info;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 256)]
    string sn_info;
    int hw_info;
    byte hw_var;
    int fw_vers;
}

The function declaration should then be:

[DllImport("ASTAS_DLL.dll")]
public extern static int Search([In] t_DeviceInfo[] devInfPtr);

This assumes that the calling convention is stdcall. It looks to me as though it is actually cdecl. In which case you need:

[DllImport("ASTAS_DLL.dll", CallingConvention=CallingConvention.Cdecl)]
public extern static int Search([In] t_DeviceInfo[] devInf);

I've used [In] marshalling. You may need to modify that depending on the semantics, which I cannot discern from the information provided.

Answer 2

在unsafe上下文中使用fixed语句 。