MQL4 Functions

Overview

Functions are used to write code for sub-tasks, implementing stepwise refinement. A function definition consists of a header and a body.

Function Definition

**Header**: Includes return value type, function name (identifier), and formal parameters.

**Body**: Contains the instructions enclosed in braces {}.

Parameters

Maximum of 64 parameters per function.

Function Prototype

Declaration of a function, specifying return type, identifier, and argument types.

Enables strict type checking and implicit typecasting during calls.

Used in classes for code readability.

A function definition must exactly match its declaration.

Every declared function must be defined.

Return Operator

Returns the value of an expression, converted to the function's result type.

**Returnable types**: Simple types, simple structures, object pointers.

**Non-returnable types**: Arrays, class objects, variables of compound structure type.

For functions returning no value, use the void type.

Default Parameter Values

Parameters can have default values defined by constants.

If any parameter has a default value, all subsequent parameters must also have default values.

Related Concepts

Function Call

Passing Parameters

Function Overloading

Operation Overloading

External Functions

Exporting Functions

Event Handling Functions

Overload

Virtual Functions

Polymorphism