memory mapp file write C++ read in mql4

External question — Stack Overflow Stack Exchange Author: faust Original post: https://stackoverflow.com/questions/64213192 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. 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

External answer — Stack Overflow Stack Exchange Author: MartinVeronneau Original post: https://stackoverflow.com/a/64214500 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. 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; }

External answer — Stack Overflow Stack Exchange Author: sbsohrabi Original post: https://stackoverflow.com/a/75354426 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. strings are unicode in MQL, or similarly 2-bytes wchat_t in C++. Here is a sample : #include <cstdlib> #include <cstring> #include <string> char* pBufMQL; std::wstring ss = L"Sample string"; CopyMemory((PVOID)pBufMQL, ss.c_str(), ss.size() * sizeof(wchar_t)); in MQL: handle = OpenFileMappingW( FILE_MAP_ALL_ACCESS, FALSE, szName); if(handle == 0) { Alert("Could not open file mapping object", GetLastError()); } string Data = MapViewOfFile(handle, FILE_MAP_ALL_ACCESS, 0, 0, BUF_SIZE); Print("Done, size: ", StringLen(Data), "-", Data); p.s. 1: I'm currently struggling with writing from MQL to the buffer and string in MQL are a copy of pBuf(from C++), converted to string. And I need to modify buffer from MQL. p.s. 2: p.s. 1 solved, Here is a working example : https://www.mql5.com/en/articles/364#3