C# 和 C++，out 参数在方法中不返回任何内容

Question

I need help with a method, it is a method imported from a dll, the method is in C++ and it is the following:

DECLSPEC int WINAPI I15693_Inventorys(HID_DEVICE device, BYTE *pData, BYTE *pLen);

The correct translation to C# is this (Provided by the manufacturer):

public static extern int I15693_Inventorys(IntPtr device, byte[] pData, ref byte pLen);

The problem is that the method has 2 OUT parameters (The pData and pLen ones), one of which has a ref and the other does not, I need the value of the second parameter's out but I can't get it, does not return anything, if I modify the method and add a ref for that parameter the program crashes, any ideas? This is my code:

byte[] chip = Array.Empty<byte>();
byte longitud = 0;
_ = RFIDReader.Sys_SetAntenna(g_hDevice, 0);
_ = RFIDReader.Sys_InitType(g_hDevice, 1);
_ = RFIDReader.Sys_SetAntenna(g_hDevice, 1);
int resultado = RFIDReader.I15693_Inventorys(g_hDevice, chip, ref longitud);

Oh, and the method returns me an error code of 0, which executes correctly, but without returning anything from the second parameter. Also say that the method in c++ seems that both parameters have a pointer, so in its translation both should have a ref, right?

EDIT:

Answer 1

You should pin the value for handling in unmanaged memory.

byte longitud = 0;
GCHandle gch = GCHandle.Alloc(longitud, GCHandleType.Pinned);

// Call your function
int resultado = RFIDReader.I15693_Inventorys(g_hDevice, chip, ref longitud);

gch.Free();