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MQL5 FileOpen Guide: Reading & Writing CSV Files in MetaTrader 5

Comprehensive guide to MQL5 FileOpen for CSV files. Learn how to combine FILE_READ, FILE_WRITE, FILE_CSV, and FILE_COMMON flags, format custom delimiters, and stream trade records safely.

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What this MQL5 guide covers

FileOpen returns an integer file handle on success or INVALID_HANDLE (-1) on error.

MQL5 restricts file access to the terminal sandbox (MQL5\Files) unless FILE_COMMON is specified to access the shared OS directory.

Combining FILE_CSV with FILE_READ and FILE_WRITE requires explicit delimiter specification (e.g. comma ',' or semicolon ';').

Always enclose file operations in resource protection blocks and invoke FileClose(handle) to flush disk buffers and prevent file locking.

FileOpen Function Signature and Bitmask Flags

MQL5 provides low-level file input/output through the FileOpen function. It opens files in text, binary, or delimited CSV mode, controlling access permissions and sharing policies.

FlagValue TypePurpose
FILE_READOpen flagOpens file for reading input data
FILE_WRITEOpen flagOpens file for writing (creates or overwrites existing file)
FILE_CSVFormat flagSpecifies comma/delimited text file where FileWrite inserts delimiters automatically
FILE_ANSIEncoding flagEncodes strings as 1-byte ANSI characters (recommended for external tools/Python)
FILE_COMMONLocation flagDirects path to shared Common\Files directory across all MT5 terminals
FILE_SHARE_READSharing flagAllows other applications or EAs to read the file simultaneously

Terminal Sandbox vs FILE_COMMON Directory

For security reasons, MetaTrader 5 isolates file operations within dedicated directory sandboxes. Without FILE_COMMON, files are written to [Terminal Data Folder]\MQL5\Files. Other terminal instances cannot access this folder.

Adding FILE_COMMON directs the file to C:\Users\[User]\AppData\Roaming\MetaQuotes\Terminal\Common\Files. This shared folder enables seamless communication between multiple EAs, Python data analysis pipelines, and external charting tools.

  • Local Sandbox: FileOpen("log.csv", FILE_WRITE | FILE_CSV); -> MQL5\Files\log.csv
  • Shared Directory: FileOpen("log.csv", FILE_WRITE | FILE_CSV | FILE_COMMON); -> Common\Files\log.csv
  • Subdirectories: You can specify relative subfolders such as "Data\\EURUSD.csv".

Reading CSV Records Row by Row

When reading a CSV file opened with FILE_CSV, each call to FileReadString(handle) reads the next token up to the delimiter or newline.

Looping while !FileIsEnding(handle) enables parsing complete multi-column tables into MQL5 structs or arrays.

Implementation details & mechanics

Core implementation pattern

To log trading activity or export trade history to CSV: call FileOpen with FILE_WRITE | FILE_CSV | FILE_ANSI | FILE_COMMON. Write a header row using FileWrite(handle, "Ticket", "Symbol", "Type", "Volume", "Price", "Time"). When a trade executes, append the trade metrics with FileWrite.

Error handling & safety rules

Always verify if the file handle is valid before performing I/O: if(handle == INVALID_HANDLE) log GetLastError(). Once read or write loops terminate, unconditionally invoke FileClose(handle) so the operating system commits buffered data to disk.

MQL5 Code Implementation Code

//+------------------------------------------------------------------+
//|                                             FileOpenCSVGuide.mq5 |
//|                             Copyright 2026, Pineify Guides Series |
//|                                              https://pineify.app |
//+------------------------------------------------------------------+
#property copyright "Pineify Guides Series"
#property link      "https://pineify.app/mql5/fileopen-csv-guide"
#property version   "1.00"
#property script_show_inputs

//--- Input parameters
input string InpFileName = "pineify_trades.csv"; // CSV File Name
input bool   InpUseCommonFolder = true;         // Use Shared Common\Files Folder

//+------------------------------------------------------------------+
//| Function: Write trade records to CSV                             |
//+------------------------------------------------------------------+
bool WriteTradeLogCSV(const string filename, bool useCommon)
  {
   int flags = FILE_WRITE | FILE_CSV | FILE_ANSI;
   if(useCommon)
      flags |= FILE_COMMON;

   // Open file for writing with comma ',' delimiter
   int fileHandle = FileOpen(filename, flags, ',');
   if(fileHandle == INVALID_HANDLE)
     {
      PrintFormat("Failed to open file %s for writing. Error: %d", filename, GetLastError());
      return false;
     }

   // 1. Write Header Row
   FileWrite(fileHandle, "Timestamp", "Symbol", "Action", "Lots", "Price", "Comment");

   // 2. Write Data Rows
   FileWrite(fileHandle,
             TimeToString(TimeCurrent(), TIME_DATE|TIME_SECONDS),
             _Symbol,
             "BUY",
             0.10,
             SymbolInfoDouble(_Symbol, SYMBOL_ASK),
             "Initial Entry");

   FileWrite(fileHandle,
             TimeToString(TimeCurrent(), TIME_DATE|TIME_SECONDS),
             _Symbol,
             "MODIFY_SL",
             0.10,
             SymbolInfoDouble(_Symbol, SYMBOL_BID),
             "Trailing Stop Step");

   // 3. Close File Handle
   FileClose(fileHandle);
   PrintFormat("Successfully wrote CSV records to %s", filename);
   return true;
  }

//+------------------------------------------------------------------+
//| Function: Read and parse CSV file records                        |
//+------------------------------------------------------------------+
bool ReadTradeLogCSV(const string filename, bool useCommon)
  {
   int flags = FILE_READ | FILE_CSV | FILE_ANSI;
   if(useCommon)
      flags |= FILE_COMMON;

   int fileHandle = FileOpen(filename, flags, ',');
   if(fileHandle == INVALID_HANDLE)
     {
      PrintFormat("Failed to open file %s for reading. Error: %d", filename, GetLastError());
      return false;
     }

   Print("--- Reading CSV Data ---");
   int lineNum = 0;

   // Loop until end of file
   while(!FileIsEnding(fileHandle))
     {
      // Read each column token
      string col1 = FileReadString(fileHandle);
      if(FileIsEnding(fileHandle) && col1 == "")
         break;

      string col2 = FileReadString(fileHandle);
      string col3 = FileReadString(fileHandle);
      string col4 = FileReadString(fileHandle);
      string col5 = FileReadString(fileHandle);
      string col6 = FileReadString(fileHandle);

      lineNum++;
      PrintFormat("Row %d: [%s] | Symbol: %s | Action: %s | Lots: %s | Price: %s | Note: %s",
                  lineNum, col1, col2, col3, col4, col5, col6);
     }

   FileClose(fileHandle);
   PrintFormat("Finished reading %d rows from %s", lineNum, filename);
   return true;
  }

//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
  {
   // Demo: Write sample records, then read them back
   if(WriteTradeLogCSV(InpFileName, InpUseCommonFolder))
     {
      ReadTradeLogCSV(InpFileName, InpUseCommonFolder);
     }
  }

Copy this code into MetaEditor, save it in your MQL5 folder (Experts, Scripts, or Include), and compile with F7.

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Frequently Asked Questions

Related MQL5 pages

String Conversion Guide→Datetime Guide→Ctrade Class Guide→Ordersend Guide→

Technical references

Risk and testing note

Past performance is not indicative of future results. Backtest statistics are based on historical data and do not guarantee future profits. Trading involves significant risk of loss. This content is for educational purposes only and does not constitute financial advice.