如何从C#中PInvoke C++DLL函数

我正试图从C#应用程序中访问显微镜。SDK是用C++编写的，我不能在应用程序中添加Dlls作为引用（因为它们是非托管代码）。因此，我发现我需要使用DllImport才能使用C#中的函数。

不幸的是，这似乎超出了我的想象。

举个例子，一些C++代码（来自SDK中的一个示例应用程序）：

interface Camera;
typedef Camera * CameraHandle;
struct CameraInfo
{
  wchar_t               camera_name[64];        // camera head type
  wchar_t               controller_name[64];    // controller type
  wchar_t               firmware_version[64];   // firmware version
  long                  lib_id;                 // library ID
  long                  controller_id;          // controller ID
  long                  camera_id;              // camera ID
  CameraHandle          handle;                 // handle to opened camera
  long                  status;                 // status (0 = available)
  CameraInfo()
  {
    memset(this,0,sizeof(*this));
  }
};
typedef struct CameraInfo CameraInfo;
CamDiscoverCameras(OUT const struct CameraInfo ** info, OUT long * count);

这就是它以后的使用方式：

CamResult               result;          //enum CamResult{...}
const CameraInfo*       camera_info  = NULL;
long                    camera_count = 0, pre_lib_id, pre_controller_id;
result = CamDiscoverCameras(&camera_info, &camera_count);

如何将其转换为C#代码？我已经尝试过类似的东西：

    [StructLayout(LayoutKind.Sequential)]
    struct CameraInfo
    {
        string              camera_name;            // camera head type
        string              controller_name;        // controller type
        string              firmware_version;       // firmware version
        int                 lib_id;                 // library ID
        int                 controller_id;          // controller ID
        int                 camera_id;              // camera ID
        public IntPtr       handle;                 // handle to opened camera
        int                 status;                 // status (0 = available)
    }
    [DllImport("Cam.dll", EntryPoint = "CamDiscoverCameras")]

但基本上我不知道我在做什么，下一步需要做什么（比如需要如何定义函数，如何处理C++代码中的"接口"，结构是否正确转换等等）。

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
struct CameraInfo
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 64)]
    string camera_name;            // camera head type
...

[DllImport("Cam.dll", EntryPoint = "CamDiscoverCameras")]
// you can create enum of ints here and return it
static extern int CamDiscoverCameras(out IntPtr info, out int count);
CameraInfo DiscoverCameraInfos()
{
    IntPtr info; int count;
    int camResult = CamDiscoverCameras(out info, out count);
    var camInfo = (CameraInfo) Marshal.PtrToStructure(info, typeof(CameraInfo));
    // cleanup code - pass your IntPtr to C++ code
    // for it to delete the struct as it seems it was allocated there
    return camInfo;
}