Mql4: Using `StringSplit()` to Parse Custom Data from `OrderComment()`

In MQL4, there is no dedicated "metadata" field for orders. However, you can save extra information using two specific properties of an order:

1. Magic Number (int): The most robust method. It is a unique integer identifier assigned by the EA. Brokers do not modify this value.
2. Order Comment (string): A text field. While easier to read, it is unreliable because brokers often overwrite comments (e.g., during partial closes or stop-loss triggers).

The best practice is to use the Magic Number to identify the strategy logic and map that number to a name within your code.

Implementation: Using Magic Numbers to Identify Strategies

The following code demonstrates a robust framework. It defines unique IDs for different strategies, assigns them when opening orders, and includes a helper function to read that ID and return the human-readable strategy name.

//+------------------------------------------------------------------+
//|                                       StrategyIdentifier_Demo.mq4|
//|                        Copyright 2023, MetaQuotes Software Corp. |
//|                                             https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2023, MetaQuotes Software Corp."
#property link      "https://www.mql5.com"
#property version   "1.00"
#property strict

//--- 1. Define Unique IDs for your strategies
#define STRATEGY_TREND_FOLLOWING 1001
#define STRATEGY_MEAN_REVERSION  1002
#define STRATEGY_SCALPER         1003

//--- Input parameters
input double Lots = 0.1;
input int    StopLoss = 50;
input int    TakeProfit = 100;

//+------------------------------------------------------------------+
//| Expert initialization function                                   |
//+------------------------------------------------------------------+
int OnInit()
  {
   // Example: Open two trades with different Strategy IDs for testing
   // Note: In a real EA, this would happen based on logic in OnTick
   
   if(OrdersTotal() == 0) 
     {
      // Open a Buy using the Trend Strategy ID
      OpenTrade(OP_BUY, STRATEGY_TREND_FOLLOWING);
      
      // Open a Sell using the Mean Reversion Strategy ID
      OpenTrade(OP_SELL, STRATEGY_MEAN_REVERSION);
     }
     
   return(INIT_SUCCEEDED);
  }

//+------------------------------------------------------------------+
//| Expert tick function                                             |
//+------------------------------------------------------------------+
void OnTick()
  {
   // Periodically check open orders to see which strategy opened them
   ReportOpenOrders();
  }

//+------------------------------------------------------------------+
//| Helper: Open a trade with a specific Magic Number (Strategy ID)  |
//+------------------------------------------------------------------+
void OpenTrade(int type, int strategyID)
  {
   double price, sl, tp;
   
   if(type == OP_BUY)
     {
      price = Ask;
      sl = (StopLoss > 0) ? price - StopLoss * Point : 0;
      tp = (TakeProfit > 0) ? price + TakeProfit * Point : 0;
     }
   else
     {
      price = Bid;
      sl = (StopLoss > 0) ? price + StopLoss * Point : 0;
      tp = (TakeProfit > 0) ? price - TakeProfit * Point : 0;
     }

   // --- CRITICAL STEP ---
   // The 'strategyID' is passed as the 'magic' parameter (2nd to last)
   int ticket = OrderSend(_Symbol, type, Lots, price, 3, sl, tp, "Trade Comment", strategyID, 0, clrNONE);
   
   if(ticket < 0)
     {
      Print("OrderSend failed with error #", GetLastError());
     }
   else
     {
      Print("Order Opened. Ticket: ", ticket, " | Strategy ID: ", strategyID);
     }
  }

//+------------------------------------------------------------------+
//| Helper: Convert Magic Number ID to String Name                   |
//+------------------------------------------------------------------+
string GetStrategyName(int magicNumber)
  {
   switch(magicNumber)
     {
      case STRATEGY_TREND_FOLLOWING: return("Trend Following");
      case STRATEGY_MEAN_REVERSION:  return("Mean Reversion");
      case STRATEGY_SCALPER:         return("Scalper");
      default:                       return("Unknown/Manual");
     }
  }

//+------------------------------------------------------------------+
//| Logic: Loop through orders and identify their origin             |
//+------------------------------------------------------------------+
void ReportOpenOrders()
  {
   int total = OrdersTotal();
   
   for(int i = 0; i < total; i++)
     {
      if(OrderSelect(i, SELECT_BY_POS, MODE_TRADES))
        {
         // 1. Get the Magic Number
         int magic = OrderMagicNumber();
         
         // 2. Translate it to a name
         string stratName = GetStrategyName(magic);
         
         // 3. Print the info
         Print("Ticket #", OrderTicket(), 
               " | Symbol: ", OrderSymbol(), 
               " | Magic: ", magic, 
               " | Strategy: ", stratName);
        }
     }
  }
//+------------------------------------------------------------------+

Key Concepts Explained

1. #define Constants:
   We define readable names for integer IDs (e.g., STRATEGY_TREND_FOLLOWING is 1001). This prevents "magic number" confusion in the code.

2. OrderSend Parameter:
   The OrderSend function signature is:
   OrderSend(symbol, cmd, volume, price, slippage, sl, tp, comment, magic, expiration, arrow_color)
   We pass our Strategy ID into the 9th parameter (magic).

3. OrderMagicNumber():
   When looping through orders using OrderSelect, this function retrieves the integer we saved during OrderSend.

4. GetStrategyName():
   Since the order only stores an integer (1001), we use a switch statement to map that integer back to a human-readable string ("Trend Following") for logging or on-screen display.

Alternative: Using Comments (Not Recommended)

You can pass a string to the 8th parameter of OrderSend (the comment field).

OrderSend(_Symbol, OP_BUY, Lots, Ask, 3, 0, 0, "TrendStrategy", 0, 0, clrNONE);

And read it back using:

string comment = OrderComment();

Why this is dangerous:
If you perform a partial close (e.g., closing 0.5 lots of a 1.0 lot position), the broker/server will automatically change the comment of the remaining position to something like "from #123456". Your original strategy tag ("TrendStrategy") will be deleted, and your code will lose track of the trade. Magic Numbers persist through partial closes.

Q&A: Trade Metadata in MQL4

Q: Can I change the Magic Number of an open trade?
A: No. The Magic Number is assigned when the order is created and cannot be modified via OrderModify. It is immutable for the life of the order.

Q: Can I store more complex data, like the value of an indicator at the time of entry?
A: Not directly in the order. To do this, you must use the Magic Number as a "Key". You would write the complex data to a CSV file or a Global Variable using the Order Ticket or Magic Number as the reference ID, and look it up later.

Q: What happens if I restart the terminal?
A: Magic Numbers are stored on the trade server. If you restart your terminal or move to a different computer, OrderMagicNumber() will still retrieve the correct ID.

Q: How do I handle manual trades?
A: Manual trades usually have a Magic Number of 0. You can handle this in your GetStrategyName function (as shown in the default case in the code above).