PInvoke错误将C ++ dll封送入C＃，将结构传递给方法

Question

Hi all I am trying to compile a C++ project into a DLL and then use the Structs and methods from C#. I made an openCV program and I need to pass data back and forth. For now I am trying simple things to get familiar with the language since it is the first time I touch C++ and C# ...

So in C++ I have :

#pragma pack(push, 2)  
typedef struct 
{
//char *plate;
unsigned int width;
unsigned int height;
//bool hasPlateOn;
//unsigned char *imgData;
} Sframe;
extern "C" Sframe MYCVAPI findPossiblePlates(Sframe& in)

And I try to use it from C# like this :

 [StructLayout(LayoutKind.Sequential)]
    struct Sframe
    {
       // [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]
       // char[] plate;
        [MarshalAs(UnmanagedType.U4)]
        int width;
        [MarshalAs(UnmanagedType.U4)]
        int height;
       // bool hasPlateOn;
      //  [MarshalAs(UnmanagedType.ByValArray, SizeConst = 10)]
      //  char[] imgData;
    }

  [DllImport(@"ALPR_pwv.dll",CallingConvention=CallingConvention.Cdecl,EntryPoint = "findPossiblePlates")]
    static extern Sframe findPossiblePlates(Sframe infoOut);

But no matter what I try I get errors that the method's type signature is not PInvoke compatible.

is there anyone that could help me understand this issue?

Is it even possible to pass and get custom structs among C++ and C# ?

because the end stuct will be much more complex in the end since I have to pass images with data like coordinates etc...

Answer 1

正如@SaniSinghHuttunen所提到的，我错过了ref关键字，不得不使用MarshalAs.U4 ...再次感谢:)