Call VC++ dll in C# Application

Question

HI we are using one c++ dll to read data from Hardware. Following is the function defination from C++ dll. LRESULT CALLBACK MT_Read_Holding_Reg(long llSocketHandleUCHAR lucDevIDUSHORT lunAddressUSHORT lunQuantity USHORT* lunHLData); To Call this from C# I have written following code: [DllImport(MT_TCP_Read.dll CharSet = CharSet.Ansi SetLastError = true ExactSpelling = true)] public static extern int MT_Read_Input_Reg(int llSocketHandle byte lucDevID short lunAddress short lunQuantity ref short lunHLData); and while calling this function I have writtten following code: short[] arr_hg = new short[3]; int ret = -1; ret = MT_Read_Coils(handle 1 100 3 ref arr_coils[0]); This function return no data where as same dll used in VB6 return correct data. Is there any problem in above code. Any help appreciated. Regards Vikram

Sam Hobbs · Answer

In C++ LRESULT can be either 32-bits or 64-bits so we need to use IntPtr for it. So change the type that is returned from int to IntPtr .

Vulpes · Answer

See if you have any better luck with this C# signature: [DllImport(MT_TCP_Read.dll CharSet = CharSet.Ansi SetLastError = true ExactSpelling = true)] public static extern int MT_Read_Input_Reg(int llSocketHandle byte lucDevID ushort lunAddress ushort lunQuantity [MarshalAs(UnmanagedType.LPArray SizeConst = 3)] ushort[] lunHLData); and then call with: ushort[] arr_hg = new ushort[3]; int ret = MT_Read_Coils(handle 1 100 3 arr_hg);