Developer Support Languages VC++, C# and VB.NET

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Troubleshooting PInvoke Related Issues 
I am back with some more PInvoke Stuff.  Recently I was working on a PInvoke issue which I found interesting. 
I have a C++ dll which has a function whose signature is
int TestFunc(IN_STRUCT in_Params, RET_STRUCT * pret_Par). 
I wanted to call this function from C#.  Function has two arguments.  First argument is input structure which will be filled from C# code and passed to C++ code.  Second argument is output structure which is filled in C++ code and output to C# code.
 Here are the C struct definitions and a function that needs to be marshaled
#include "stdafx.h"
#include <stdio.h>
#include "Objbase.h"
#include <malloc.h>
 
 
typedef struct IN_STRUCT
{
      BYTE CMD_PType;
      BYTE CMD_PTType;
      BYTE CMD_OC;     
      BYTE CMD_Seq;
     
};
 
typedef struct RET_STRUCT    
{
  
      BYTE RET_OC;
      BYTE RET_Seq;
      BYTE RET_RetBytes;
      char *str;
      BYTE RET_PD[10];
     
};
 
 
extern "C"  __declspec(dllexport) \
        int TestFunc(IN_STRUCT in_Params, RET_STRUCT * pret_Par)
{
 
      int iRet = 0;
      pret_Par->RET_OC = in_Params.CMD_OC;
      pret_Par-