MQL4 Conditional Compilation

Overview

Preprocessor directives that enable or disable code sections during compilation based on defined identifiers.

Directives

**#ifdef identifier**

* Compiles the enclosed code if identifier has been defined via #define.

**#ifndef identifier**

* Compiles the enclosed code if identifier has NOT been defined via #define.

**#else**

* Used within #ifdef or #ifndef blocks. * If the preceding condition is false, the code following #else is compiled.

**#endif**

* Marks the end of a conditional compilation block.

Structure

Directives can be chained with #else to create if-else like structures. The compiler ignores code blocks based on the evaluation of the conditions.

#ifndef TestMode
   #define TestMode
#endif
void OnStart()
{
   #ifdef TestMode
      Print("Test mode");
   #else
      Print("Normal mode");
   #endif
}

Standard Macros

The following macros are automatically defined based on the compilation context:

__MQL4__: Defined when compiling .mq4 files.

__MQL5__: Defined when compiling .mq5 files.

_DEBUG: Defined when compiling in debug mode.

_RELEASE: Defined when compiling in release mode.

**Example Usage:**

void OnStart()
{
   #ifdef __MQL5__
      #ifdef _DEBUG
         Print("Hello from MQL5 compiler [DEBUG]");
      #else
         #ifdef _RELEASE
            Print("Hello from MQL5 compiler [RELEASE]");
         #endif
      #endif
   #else
      #ifdef __MQL4__
         #ifdef _DEBUG
            Print("Hello from MQL4 compiler [DEBUG]");
         #else
            #ifdef _RELEASE
               Print("Hello from MQL4 compiler [RELEASE]");
            #endif
         #endif
      #endif
   #endif
}

Related Directives

#define (Macro substitution)

#property (Program properties)

#include (Including files)

#import (Importing functions)