memory mapp file write C++ read in mql4

Question

hi guys i want read a memory mapped file created by C++ program , i use the MSDN example for create in C++ the memory mapped file , i want read the string in my metatrader 4 i write this code

#property copyright "Copyright © 2005, MetaQuotes Software Corp."
#property link      "http://www.metaquotes.net/"

#property indicator_separate_window
#property indicator_minimum 0
#property indicator_buffers 1
#property indicator_color1 Blue
#define FILE_MAP_READ           4

#define BUF_SIZE 256
extern string szName = "MyFileMappingObject";
//extern string szName = "Global\\dllmemfilemap";
int handle = 0;
string  Data;

#import "kernel32.dll"
int OpenFileMappingA(int dwDesiredAccess, bool bInheritHandle, string lpName);
string  MapViewOfFile(int hFileMappingObject, int dwDesiredAccess, int dwFileOffsetHigh, int dwFileOffsetLow, int dwNumberOfBytestoMap);
int CloseHandle( int handle);
int UnmapViewOfFile(string lpBaseAddress);
#import
//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
int start()
  {
   handle = OpenFileMappingA(FILE_MAP_READ, FALSE, szName);
   if(handle == 0)
   {
      Alert("Could not open file mapping object", GetLastError());
   }
   else
   {
   Data = MapViewOfFile(handle, FILE_MAP_READ, 0, 0, BUF_SIZE);
   Alert(Data);
   UnmapViewOfFile(Data);
   CloseHandle(handle);
   }
   return (0);
  }

//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int init()
  {
   return(0);
  }

but not open the OpenFileMappingA, return always 0 , anyone have some idea ? thankz at all

Answer 1

You need to call CreateFileMapping before trying to OpenFileMapping .

See example here :

#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>

#define BUF_SIZE 256
TCHAR szName[]=TEXT("Global\\MyFileMappingObject");
TCHAR szMsg[]=TEXT("Message from first process.");

int _tmain()
{
   HANDLE hMapFile;
   LPCTSTR pBuf;

   hMapFile = CreateFileMapping(
                 INVALID_HANDLE_VALUE,    // use paging file
                 NULL,                    // default security
                 PAGE_READWRITE,          // read/write access
                 0,                       // maximum object size (high-order DWORD)
                 BUF_SIZE,                // maximum object size (low-order DWORD)
                 szName);                 // name of mapping object

   if (hMapFile == NULL)
   {
      _tprintf(TEXT("Could not create file mapping object (%d).\n"),
             GetLastError());
      return 1;
   }
   pBuf = (LPTSTR) MapViewOfFile(hMapFile,   // handle to map object
                        FILE_MAP_ALL_ACCESS, // read/write permission
                        0,
                        0,
                        BUF_SIZE);

   if (pBuf == NULL)
   {
      _tprintf(TEXT("Could not map view of file (%d).\n"),
             GetLastError());

       CloseHandle(hMapFile);

      return 1;
   }


   CopyMemory((PVOID)pBuf, szMsg, (_tcslen(szMsg) * sizeof(TCHAR)));
    _getch();

   UnmapViewOfFile(pBuf);

   CloseHandle(hMapFile);

   return 0;
}