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+--- Thema: MQL4 vs. MQL5: A Programmer's Deep Dive into MetaTrader Development** (/showthread.php?tid=46)
MQL4 vs. MQL5: A Programmer's Deep Dive into MetaTrader Development** - indigostrader - 21.11.2025
MQL4 vs. MQL5: A Programmer's Deep Dive into MetaTrader Development**
**Posted by:** INDIGOSTRADER.com
**Category:** MQL4 & MQL5 Programming
**Tags:** #MQL5, #MQL4, #Programming, #EA, #Indicator, #MetaTrader, #OOP, #Performance
Hello fellow coders,
Whether you're a seasoned developer new to trading or a trader looking to level up your automation skills, understanding the core programming differences between MQL4 and MQL5 is crucial. This post isn't just about which is "better"; it's a technical breakdown of their architectures, syntax, and capabilities from a software engineering standpoint. Let's dive into the details that matter when you're staring at an IDE.
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At its heart, the difference is evolutionary: **MQL5 is a significant step forward into modern object-oriented programming (OOP), while MQL4 is a simpler, procedural language.**
| Feature | MQL4 | MQL5 | Programmer's Takeaway |
| :--- | :--- | :--- | :--- |
| **Programming Paradigm** | Primarily Procedural | Fully Object-Oriented | MQL5 enables better code organisation, reusability, and encapsulation through classes, inheritance, and polymorphism. |
| **Execution Model** | Single-threaded, Sequential `start()` function. | Event-Driven. Separate handlers like `OnTick()`, `OnTimer()`, `OnChartEvent()`. | MQL5 is cleaner and more efficient. Your code runs only when a relevant event occurs, leading to less wasteful CPU cycles. |
| **Language Syntax** | C-like. | C++-like. | The syntax is very similar, making the transition easier. The key difference is the addition of OOP keywords (`class`, `public`, `private`, etc.) in MQL5. |
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This is where the rubber meets the road for development.
**3.1. Data Access and Pricing Models**
* **MQL4:** Uses a limited set of pre-defined arrays like `Open[]`, `Close[]`, `High[]`, `Low[]`. The `iMA`, `iRSI` functions return a handle to be used in copying.
* **MQL5:** Introduces the **Copy Functions** (`CopyBuffer()`, `CopyRates()`) and a more robust **Handle-based system**. You get a handle for an indicator (e.g., `iMA(_Symbol, _Period, ...)`) and then use `CopyBuffer` to retrieve the data.
* **Programmer's Advantage:** The MQL5 model is more flexible and powerful. It allows for easy access to any symbol/timeframe and provides clearer error handling when data retrieval fails.
**3.2. Order Management (The Biggest Change)**
This is the most critical area to understand when porting code.
| Action | MQL4 | MQL5 |
| :--- | :--- | :--- |
| **Buy Order** | `OrderSend(Symbol(), OP_BUY, ...)` | `OrderSend(_Symbol, ORDER_TYPE_BUY, ...)` |
| **Check Result** | Relies on `GetLastError()` | Returns a `bool` and fills a `MqlTradeResult` struct. |
| **Order Selection** | `OrderSelect()` by ticket or position. | Different functions: `OrderGetTicket()`, `PositionGetInteger()`, `HistoryOrderGetInteger()`. |
* **Programmer's Takeaway:** MQL5 has a **clear separation between pending orders, open positions, and historical deals/orders**. This is a much cleaner and more accurate representation of a trading account. The `CTrade` class in the Standard Library further simplifies this with methods like `Buy()` and `Sell()`.
**3.3. Debugging and Testing**
* **MQL4:** Relies heavily on `Print()`, `Comment()`, and the old Strategy Tester.
* **MQL5:** Features a powerful **integrated debugger** (breakpoints, step-in/over, watch variables). The Strategy Tester is vastly superior, supporting multi-threaded testing, real tick data, and detailed optimization reports.
* **Programmer's Advantage:** The MQL5 toolchain dramatically improves development speed and code reliability. The ability to debug an Expert Advisor step-by-step is a game-changer.
**3.4. Graphical Objects and User Interaction**
* **MQL4:** Basic object creation functions (`ObjectCreate`).
* **MQL5:** Enhanced object management and, crucially, support for **`OnChartEvent()`**. This allows your EAs/scripts to react to mouse clicks, keyboard presses, and object clicks, enabling the creation of complex interactive dashboards.
**3.5. Standard Library**
* **MQL4:** Limited standard library.
* **MQL5:** Ships with a comprehensive **Standard Library**, including ready-to-use classes for trade operations (`CTrade`), indicators (`CiMA`), and charts (`CChart`). This promotes code reuse and reduces boilerplate.
* **Choose MQL4 if:**
* You are maintaining legacy EAs or indicators for MetaTrader 4.
* Your broker or prop firm only supports MT4.
* You are a complete beginner and want the simplest possible introduction to trading automation (though starting with MQL5's basics is also valid).
* **Choose MQL5 if:**
* You are starting a **new project**.
* You value **code quality, organization, and maintainability** (OOP principles).
* You need **advanced performance, testing, and debugging**.
* You require **complex user interfaces** on the chart.
* You want access to more **financial instruments and timeframes**.
**For a programmer, the choice is clear: for all new development, MQL5 is the superior platform.**
---
1. **Trying to "Port" Code Line-by-Line:** Don't. Understand the new event-driven and order management models first, then re-architect your logic.
2. **Ignoring the Standard Library:** Reinventing the wheel for trade execution is a waste of time. Use `CTrade`.
3. **Misunderstanding the Data Model:** Assuming `Close[0]` works the same way. Remember to use `CopyRates()` or the `CiClose` class.
4. **Forgetting Error Handling:** While MQL5's `OrderSend` returns a boolean, you must still check the `MqlTradeResult` and `MqlTradeCheckResult` structs for detailed error information.
MQL4 is a capable but dated language. MQL5 represents the modern, robust, and professional path for algorithmic trading development on the MetaTrader platform. Embracing its object-oriented nature and event-driven architecture will make you a more effective and efficient programmer.
**Let's discuss!**
* What has been your biggest challenge when moving from MQL4 to MQL5?
* For the seasoned MQL5 developers: What's your favorite feature or Standard Library class?
* Do you think MQL4 will ever be completely phased out?
Happy coding!
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*Disclaimer: All code examples are simplified for illustrative purposes. Always implement proper error handling in your live trading systems.*