Variables

A variable is a "storage container" or "named placeholder" for data. You can read and modify the data once this container is created.

Requirements

The following links guide to the basics to understand this article:

• Introduction to Arma Scripting
• Identifier

Initialization

The first thing to do to create a variable is to find its name, also called identifier; this name must be speaking to the reader. Once you find a proper name, you have to tell the game engine that you are going to use this identifier. This is called initialization or declaration. This is how it is done:

myVariable = 0;

Before Arma 2, querying undefined (or uninitialized) variables returns nil (undefined value); from Arma 2 and later, it returns an "Error Undefined variable in expression" error.

ⓘ

An undefined (nil) variable converted to String with str will return scalar bool array string 0xe0ffffef (in Armed Assault) and scalar bool array string 0xfcffffef (in Operation Flashpoint).
Unless trying to emulate isNil, always declare your variable before trying to access it.

Deletion

Once created, variables will take up space in the computer's memory. This is not drastic for small variables, but if a big number of very large variables is used, some unneeded ones should be undefined in order to free up memory. This can be done by setting their value to nil.

hugeVariable = nil;

This effectively destroys a variable as if it had never existed.

ⓘ

Local variables are automatically freed (deleted from memory) when their scope is exited, avoiding the need to manually deallocate them.

Scopes

Variables are only visible in certain scopes of the game. This prevents name conflicts between different variables in different scripts.

There are three scopes:

local

A variable is only visible in the script, or function, or Control Structures in which it was defined.

global

A variable is visible on the whole computer where it was defined.

public

A global variable is broadcasted over the network and visible on all computers connected to the network.

Local Variables

Local variables are only visible in a specific script, or function, or Control Structures.

The identifier of local variables in a script always has to started with an underscore.

_myLocalVariable = 0;

In functions you should additionally mark variables as private using the command private. Otherwise, you may modify local variables of the calling script that are visible in the function.

// Since Arma 3 v1.54
private _myLocalVariable = 0;

// Before Arma 3 v1.54
private "_myLocalVariable";
_myLocalVariable = 0;

// Alternative method to private multiple local variables at the same time
private ["_myLocalVariable1", "_myLocalVariable2", (...)];
_myLocalVariable1 = 1;
_myLocalVariable2 = 2;
(...)

Global Variables

Global variables are visible on the whole computer where they are defined. Names given to units in the Mission Editor are also global variables pointing to those units, which may not be redefined or modified.

Identifiers of global variables must not start with underscore. Besides this, they use the same rules as for all identifiers.

myGlobalVariable = 0;

Public Variables

Public variables are global variables, visible on several computers in the network. You can never have true public variables, but you can emulate their behaviour.

The value of a global variable gets broadcasted over the network using publicVariable. After the call of this command the variable will have the same value on all clients. Once you modify the variable though you have to broadcast it manually again with publicVariable.

More information relative to private variable

If a private variable is initialized within a Control Structures (i.e. if, for, switch, while) its scope will stay within this structure (i.e. outside of the structure it will still be seen as undefined).

if (alive player) then { private _living = true; }; hint format ["%1", _living]; Returns an error, since the private variable was not initialized before being used within a control structure.

private _living = false; if (alive player) then { _living = true; }; hint format ["%1", _living]; Returns true since the variable was initialized before the if..then statement.
To initialize private variables so that they are available throughout the whole script (including any control structures), initialize it via the private command (e.g. private _varname;) at the beginning of the script.

Data Types

Variables may store certain values. The kind of the value specifies the type of the variable. Different operators and commands require variables to be of different types.

Read the article Data Types for more information about variable types.

Multiplayer Considerations

Storing functions ( or any callable code) into global variables without securing them with compileFinal (since Arma 3) is a very bad practice in multiplayer. The biggest security risk would be to see it being overriden by a malicious usage of publicVariable, setting potentially dangerous code in it.

The best option is to declare your function in CfgFunctions so the engine secures it for you.

If you want to manually create a global function, the best practice is the following:

myGlobalVarFunction = compileFinal preprocessFileLineNumbers "functions\directory\functionsFile.sqf";

See also

• Introduction to Arma Scripting
• Identifier
• Data Types
• Magic Variables
• private (Arma 3)
• local (Arma 2)