How to pass a pointer of data to the managed side on a C++ wrapper

[sinosoidal]

Hi, I'm doing a simple managed C++ class to grab data from a USB device and pass it to the C# side. This is my class: public __gc class Communication { private: LPVOID dataInBuffer; HANDLE _hFileHandle; int nBytesToRead; int maxPacketSize; public: Communication() { _hFileHandle = INVALID_HANDLE_VALUE; maxPacketSize = 256; dataInBuffer = malloc(sizeof(char) * maxPacketSize); nBytesToRead = maxPacketSize; } ~Communication() { if( _hFileHandle != INVALID_HANDLE_VALUE ) { CloseHandle( _hFileHandle ); } } bool OpenDevice( String* driverName ) { char* lpFileName = new char[driverName->Length + 10]; sprintf( lpFileName, "\\\\?\\%s", driverName ); _hFileHandle = CreateFile((LPCSTR) lpFileName,GENERIC_READ,0,0,OPEN_EXISTING,0,0); if( _hFileHandle == INVALID_HANDLE_VALUE ) { puts("Couldn't not open device"); } delete lpFileName; return( _hFileHandle != INVALID_HANDLE_VALUE ); } BOOL CloseDevice() { return CloseHandle( _hFileHandle ); } int GetPacket() { char outBuffer[256]; int nBytesRead = -1; if (_hFileHandle!=INVALID_HANDLE_VALUE) { ReadFile(_hFileHandle, dataInBuffer, nBytesToRead, (PULONG) &nBytesRead,0); } memset(outBuffer,0,maxPacketSize*sizeof(char)); memcpy(outBuffer,dataInBuffer,maxPacketSize*sizeof(char)); return nBytesRead; } }; My problem right now it how to pass the outBuffer variable in the GetPacket method outside the class. If I let the variable being declared inside the function, it gets erase when the function ends and my data goes with it. If I declare that variable in the class itself, the compiler says the following: 'outBuffer' : must explicitly specify __gc or __nogc for an array declared in a managed type And if I put the __gc attribute on the variable, then the compiler tells the following: 'identifier' : '__gc' can only be applied to a class, struct, interface, array or pointer So... what do I have to do in order to make this variable available in the C# side? I'm using char, because I need a signed 8-bit value on each position of the array. Can anyone give me some lights here? Thanks, Nuno

[N a v a n e e t h]

You are using the obsolete Managed C++ syntax. Are you using a compiler that don't support C++/CLI? If not, I would suggest you to rewrite this in C++/CLI. :)

Navaneeth How to use google | Ask smart questions

[amatecki]

Hi, You could try something like this:

// CnvBuffLib.h

#pragma once

#include <memory.h>;
#include <string.h>;

using namespace System;

namespace CnvBuffLib
{
public __gc class ConvertBuffer
{
const char __nogc * const _buffer;
static const int bsize = 256;

    public:
    ConvertBuffer()
    : \_buffer(new char \_\_nogc \[bsize\])
    {
    }
    
    ~ConvertBuffer()
    {
        delete \[\] \_buffer;
    }
    
    int GetPacket()
    {
        // sample of source data
        char tmp\[\] = {'t', 'e', 's', 't'};
        int tmplen = sizeof(tmp);
        
        // clear buffer
        char \_\_nogc \* \_bp = const\_cast<char\*>(\_buffer);
        \_bp = static\_cast<char\*>(memset(\_bp, 0, bsize));

        // copy data to buffer
        memcpy(\_bp, tmp, tmplen);
        
        return tmplen;
    }

    // this function copies native buffer to managed buffer (C# side)
    SByte GetData() \_\_gc \[\]
    {
        int rlen = strlen(\_buffer);
        if(rlen == 0)
        return 0;
        
        SByte result\[\] = new SByte\[rlen\];
        char \_\_pin \* presult = &result\[0\];
        
        memcpy(presult, \_buffer, rlen);
        
        return result;
    }
};

}