Where are files saved?

The default root is the terminal data folder MQL5/Files, or the testing agent MQL5/Files in Strategy Tester. FILE_COMMON selects the shared Common Files sandbox. Use TerminalInfoString to locate data roots rather than assuming a Windows user path.

How can I append without truncating?

Open with FILE_READ | FILE_WRITE and the chosen format and encoding. Check the handle, seek to SEEK_END and check its boolean result before writing. Add a header only to an empty file. FILE_WRITE alone replaces existing content. The supplied script demonstrates replacement with an explicit overwrite opt-in, not appending.

Why does FileOpen return INVALID_HANDLE?

Read the current GetLastError after a failed open. Causes include an inaccessible or invalid path, a missing file in read-only mode, or incompatible sharing permissions. Missing nested directories are created when opening for writing, so their absence alone is not necessarily an error.

Can Python read the output?

Yes, with the same delimiter and encoding. This example writes UTF-8 using FILE_ANSI plus CP_UTF8, then closes the file before reading. For concurrent access, agree on sharing flags, flush timing and incomplete-row handling. Sharing does not make several writers atomic.

Does FILE_ANSI mean ASCII?

No. Conversion uses the selected code page, defaulting to CP_ACP. Specify CP_UTF8 for UTF-8. FILE_UNICODE uses the MQL5 Unicode text mode. Match the actual file encoding and inspect non-ASCII text when integrating an external reader.

Does this script export executed trades?

No. It writes two labeled synthetic rows using current quotes and reads them as strings. The header is included in the reported row count. It neither queries trade history nor places orders, and its simple six-field parser does not handle every quoted CSV dialect.

Complete MQL5 guide & code

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

Use MQL5 FileOpen flags, explicit UTF-8 encoding and delimiter checks to write and read a small CSV example. Learn the terminal and Common Files sandbox locations, overwrite versus append behavior, and why a sample file is not a trade-history export.

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What this MQL5 guide covers

FileOpen returns a handle or INVALID_HANDLE; check write results as well as open results.

FILE_COMMON selects another allowed sandbox. It does not permit arbitrary filesystem access.

FILE_CSV defaults to a tab delimiter. Pass a comma explicitly when that is your file format.

This script writes synthetic six-column records, closes the file and reads it back. It places no trades and does not export account history.

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.

Flag	Value Type	Purpose
FILE_READ	Open flag	Opens file for reading input data
FILE_WRITE	Open flag	Opens file for writing (creates or overwrites existing file)
FILE_CSV	Format flag	Specifies comma/delimited text file where FileWrite inserts delimiters automatically
FILE_ANSI	Encoding flag	Uses the selected code page; combine FILE_ANSI with CP_UTF8 explicitly for this UTF-8 example
FILE_COMMON	Location flag	Directs path to shared Common\Files directory across all MT5 terminals
FILE_SHARE_READ	Sharing flag	Allows 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. In Strategy Tester the default root is the testing agent directory instead. These are MQL5 path restrictions, not a claim that OS tools cannot read the files.

FILE_COMMON selects the shared Common Files sandbox. Find the root with TerminalInfoString(TERMINAL_COMMONDATA_PATH), then its Files subfolder. External readers need the correct location, encoding and sharing permissions; concurrent writers still require coordination.

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.

An end-of-file loop alone does not validate row width or data types. The example checks exactly six fields per row and logs strings, including the header. It targets the simple records it writes; it is not a general parser for quoted fields containing delimiters or embedded newlines.

Implementation details & mechanics

Core implementation pattern

Save this as a script in MQL5/Scripts. It writes a header and two explicitly synthetic quote records, then reads the file. Existing files are refused unless InpAllowOverwrite is enabled; enabling it replaces the entire file. The existence check is a convenience guard, not a concurrent-writer lock. For a real trade log, source data from confirmed transactions and define an append and recovery policy separately.

Error handling & safety rules

Every successful open must reach FileClose, including failure paths. Check FileWrite for zero and report the error; a partial file may remain after failure. FILE_READ | FILE_WRITE preserves an existing file, but appending also requires a successful FileSeek to SEEK_END. Write a header only when the file is empty. Flush or close before another reader consumes the file; this is not a transaction or crash-recovery guarantee.

MQL5 Code Implementation

//+------------------------------------------------------------------+
//|                                             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_csv_example.csv"; // CSV File Name
input bool   InpAllowOverwrite = false;         // Existing files are refused by default
input bool   InpUseCommonFolder = true;         // Use Shared Common\Files Folder

//+------------------------------------------------------------------+
//| Function: Write trade records to CSV                             |
//+------------------------------------------------------------------+
bool WriteTradeLogCSV(const string filename, bool useCommon)
  {
   if(!InpAllowOverwrite && FileIsExist(filename, useCommon ? FILE_COMMON : 0))
     {
      Print("Existing file refused: ", filename);
      return false;
     }
   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, ',', CP_UTF8);
   if(fileHandle == INVALID_HANDLE)
     {
      PrintFormat("Failed to open file %s for writing. Error: %d", filename, GetLastError());
      return false;
     }

   // 1. Write Header Row
   ResetLastError();
   bool wrote = FileWrite(fileHandle, "Timestamp", "Symbol", "Action", "Lots", "Price", "Comment") > 0;

   // 2. Write Data Rows
   if(wrote) wrote = FileWrite(fileHandle,
             TimeToString(TimeCurrent(), TIME_DATE|TIME_SECONDS),
             _Symbol,
             "SAMPLE_BUY",
             0.10,
             SymbolInfoDouble(_Symbol, SYMBOL_ASK),
             "Synthetic example only") > 0;

   if(wrote) wrote = FileWrite(fileHandle,
             TimeToString(TimeCurrent(), TIME_DATE|TIME_SECONDS),
             _Symbol,
             "SAMPLE_QUOTE",
             0.10,
             SymbolInfoDouble(_Symbol, SYMBOL_BID),
             "No order was sent") > 0;

   int writeError = GetLastError();
   // 3. Close File Handle even when a write fails
   FileClose(fileHandle);
   if(!wrote)
     {
      PrintFormat("CSV write failed: %d; a partial file may remain", writeError);
      return false;
     }
   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, ',', CP_UTF8);
   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))
     {
      string cols[6];
      for(int i=0; i<6; ++i)
        {
         cols[i] = FileReadString(fileHandle);
         if(i<5 && (FileIsLineEnding(fileHandle) || FileIsEnding(fileHandle)))
           {
            PrintFormat("Short CSV row %d", lineNum+1);
            FileClose(fileHandle);
            return false;
           }
        }
      if(!FileIsLineEnding(fileHandle) && !FileIsEnding(fileHandle))
        {
         PrintFormat("Extra fields in CSV row %d", lineNum+1);
         FileClose(fileHandle);
         return false;
        }

      lineNum++;
      PrintFormat("Row %d: [%s] | Symbol: %s | Action: %s | Lots: %s | Price: %s | Note: %s",
                  lineNum, cols[0], cols[1], cols[2], cols[3], cols[4], cols[5]);
     }

   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

These educational examples require independent compilation and testing. A compile pass or an illustrative setting does not establish execution correctness or profitability. Any reported performance must be supported by reproducible data and test settings; past results do not predict future returns. Trading involves significant risk of loss. This content is not financial advice.