Using memory mapped file from .net to C++

Question

Hi, I was attemting to hack together a crude memory mapped bus from VB.net to C++. The way it´s constructed, is trying to be always present on the server side. Which supplies the data on the server side as well. At this point mismatching function calls and stock C++ actually landed me a mapped file that opens without errors. But no discerible data at the client side. Is there a way to match these together so that it actually works?

Imports System.IO.MemoryMappedFiles
Imports System.Threading
Public Class MemoryMapped

    Dim wEn As Integer
    Dim mMF As MemoryMappedFile = MemoryMappedFile.CreateNew("MM", 512)
    Dim mTex As New Mutex(True, "Mutexed", True)

    Public Sub Mapper()
        Try
            If GUIMain.OnLoad = True Then 'inherent to mother program "run once"
               Using vFind = mMF.CreateViewAccessor(0, 4) '(offset, length)

                    'mTex.WaitOne()
                    vFind.Write(0, (100)) '(offset, item "long")                   
                    mTex.ReleaseMutex()

                End Using
            End If

        Catch ex As Exception
            MsgBox("Memory File Error!")
        End Try

    End Sub
End Class

#include <windows.h>
#include <iostream>
#include <conio.h>
#include <string>

using namespace std;

//int Init;

int main()
{
	HANDLE mMF;
	PCHAR vFind = NULL;

	mMF = OpenFileMapping(
		FILE_MAP_ALL_ACCESS,
		FALSE,
		L"MM");

	if (mMF == NULL)
	{
		cout << "Failed File Mapping!" << endl;
	}

	vFind = (PCHAR)MapViewOfFile(
		mMF,
		FILE_MAP_ALL_ACCESS,
		0,
		0,    //
		256); //array size

	if (vFind == NULL)
	{
	    cout << "Failed Map View!" << endl;
	}

    cout << mFind << endl;
    CloseHandle();
    Return 0;
}

Answer 1

It appears that your VB.Net code is writing a 32-bit integer value to the memory mapped file. However, in the C++ code the pointer returned by MapViewOfFile is declared as a PCHAR instead of a pointer to an int (i.e., PINT). Following worked for me to print the integer value 100 written by VB to the mapped memory.

#include <windows.h>
#include <iostream>
#include <conio.h>
#include <string>

using namespace std;

//int Init;

int main()
{
    HANDLE mMF;
    PINT vFind = NULL;

    mMF = OpenFileMapping(
        FILE_MAP_ALL_ACCESS,
        FALSE,
        L"MM");

    if (mMF == NULL)
    {
        cout << "Failed File Mapping!" << endl;
    }

    vFind = (PINT)MapViewOfFile(
        mMF,
        FILE_MAP_ALL_ACCESS,
        0,
        0,    //
        256); //array size

    if (vFind == NULL)
    {
        cout << "Failed Map View!" << endl;
    }

    cout << *vFind << endl;

    UnmapViewOfFile(vFind);
    CloseHandle(mMF);
    return 0;
}

Answer 2

Hard to type this in without auto formatting/messes things up. Formatted here to be slightly more legible. mFind at the last cout not it.. supposed to be vFind.