MQL4 to MQL5: How to Convert Your Code

Introduction to MQL4 and MQL5

MQL4 and MQL5 are programming languages used within the MetaTrader platform for developing trading robots (Expert Advisors), custom indicators, and scripts. While MQL4 powered earlier versions, MQL5 is the current standard, offering significant improvements in performance, features, and capabilities.

Key Differences Between MQL4 and MQL5

The shift from MQL4 to MQL5 represents a substantial architectural change. Key differences include:

• Syntax: MQL5 adopts a syntax closer to C++, making it more structured and readable.
• Execution Model: MQL5 uses a new order management system. OrderSend() function is replaced with a more complex set of functions. MQL5 offers event-driven programming, crucial for high-frequency trading.
• Data Handling: MQL5 offers improved data handling capabilities and supports custom objects.
• Performance: MQL5 generally offers better performance due to its optimized compiler and execution environment, multithreading, which allows for parallel processing.
• Object-Oriented Programming (OOP): MQL5 fully supports OOP principles, enabling modular, reusable, and maintainable code. MQL4 only partially supports OOP.

Understanding the Motivation for Conversion

Converting MQL4 code to MQL5 is often necessary to:

• Leverage New Features: Access advanced functionalities in MQL5, such as improved backtesting, optimized order execution, and OOP.
• Improve Performance: Benefit from MQL5’s faster execution speeds, especially critical for complex algorithms.
• Maintain Compatibility: Ensure long-term compatibility with the MetaTrader platform, as MQL4 support may eventually be phased out.

Overview of the Conversion Process

The conversion process generally involves:

1. Code Review: Analyzing the MQL4 code to understand its logic and identify potential issues.
2. Syntax Adaptation: Translating MQL4 syntax to the equivalent MQL5 syntax.
3. Function Replacement: Replacing obsolete MQL4 functions with their MQL5 counterparts.
4. Testing and Debugging: Rigorously testing the converted code to ensure it functions correctly and efficiently.

Preparing Your MQL4 Code for Conversion

Code Review and Optimization (MQL4)

Before converting, review your MQL4 code for:

• Redundant Code: Remove any unnecessary or duplicated code segments.
• Inefficient Algorithms: Identify and optimize performance bottlenecks.
• Coding Style: Ensure the code is well-structured and documented.

Optimizing MQL4 code before conversion can simplify the translation process and improve the performance of the final MQL5 version. For example, replace inefficient loop constructs with more optimized alternatives.

Identifying Incompatible Functions and Syntax

Create a list of MQL4 functions and syntax that are not directly supported in MQL5. Key examples include:

• OrderSend: Replaced by order execution functions using trade class.
• OrderSelect: Different logic for order selection, must be reviewed for the current program logic.
• AccountBalance: The logic of getting account information has been changed.

Creating a Conversion Checklist

Develop a checklist outlining the steps required for each part of your code. This helps track progress and ensures no critical elements are missed. Your checklist should include:

• Data type conversions.
• Function replacements.
• Order processing logic.
• Indicator and library adaptations.
• Testing procedures.

Step-by-Step Conversion Guide

Data Types and Variable Declarations: Adapting to MQL5

MQL5 has more explicit data types compared to MQL4. Ensure you correctly convert data types like int, double, string, and datetime. Explicit typecasting may be necessary in some cases.

// MQL4
int count = 10;
double price = 1.2345;

// MQL5
int count = 10;
double price = 1.2345;

Handling of Orders and Positions: MQL4 vs. MQL5

Order management differs significantly between MQL4 and MQL5. In MQL5, you use the CTrade class to perform trading operations. You need to use the trade.PositionOpen, trade.OrderSend, and trade.PositionClose functions to control trading operations.

// MQL4
int ticket = OrderSend(Symbol(), OP_BUY, 1.0, Ask, 3, Bid - 20 * Point, Ask + 20 * Point, "My EA", 123, 0, Green);

// MQL5
#include <Trade\Trade.mqh>
CTrade trade;
trade.PositionOpen(Symbol(), ORDER_TYPE_BUY, 1.0, Ask, 0, Bid - 20 * _Point, Ask + 20 * _Point, "My EA");

Replacing Obsolete Functions with MQL5 Equivalents

Many MQL4 functions have been deprecated or replaced in MQL5. For example, iMA is still available but it is recommended to use object-oriented approach. Research and identify the appropriate MQL5 equivalents. Use the MQL5 reference for accurate syntax and usage.

// MQL4
double ma = iMA(NULL, 0, 20, 0, MODE_SMA, PRICE_CLOSE, 0);

// MQL5
#include <Indicators\iMA.mqh>
CI_MA *ma = new CI_MA();
ma.Create(Symbol(), PERIOD_CURRENT, 20, 0, MODE_SMA, PRICE_CLOSE);
double value = ma.GetData(0);
delete ma;

Adapting Custom Indicators and Libraries

Custom indicators and libraries may require significant modifications to work in MQL5. Ensure that you adjust the code to use MQL5 data structures, function calls, and event handling mechanisms. Consider rewriting libraries using OOP principles for better modularity.

Testing and Debugging Converted Code

Setting Up a Testing Environment in MetaTrader 5

Use the MetaTrader 5 Strategy Tester to thoroughly test your converted code. Configure realistic testing scenarios, including different market conditions and timeframes.

Debugging Techniques for MQL5 Code

MQL5 offers advanced debugging tools. Use the MetaEditor debugger to step through your code, inspect variable values, and identify errors. Utilize print statements (Print(), Comment()) strategically to trace the execution flow.

Comparing Results with Original MQL4 Code

Compare the performance and behavior of the converted MQL5 code with the original MQL4 code under identical conditions. Ensure that the trading logic remains consistent and that the converted code does not introduce unintended side effects. Use visual inspection and statistical analysis to validate the results.

Advanced Conversion Techniques and Best Practices

Utilizing Object-Oriented Programming (OOP) in MQL5

Leverage OOP principles to create modular, reusable, and maintainable code. Encapsulate trading logic into classes, use inheritance to extend functionality, and employ polymorphism for flexible design.

Multi-threading and Event Handling in MQL5

Utilize MQL5’s multi-threading capabilities to improve performance, especially for complex calculations or parallel tasks. Implement event handlers to respond to market events, such as price changes or order updates.

Optimizing MQL5 Code for Performance

Optimize your MQL5 code for speed and efficiency. Minimize unnecessary calculations, use efficient data structures, and avoid blocking operations. Profile your code to identify performance bottlenecks and optimize accordingly.