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A variable of type Void is an undefined variable.

Undefining Variables

nil can be used to undefine variables.

myVar = 1; // ... myVar = nil; // myVar is undefined

String Representation

The String representation of an undefined variable depends on its inferred type:

Data Type String

scalar bool array string 0xfcffffef (OFP)
scalar bool array string 0xe0ffffef (ArmA)

Nothing scalar bool array string nothing 0xfcffffef
Number scalar
Boolean bool
Array array


No comparison with any variables will work.


// error if (undefinedVar == definedVar) then { /* ... */ };
// error if (undefinedVar == undefinedVar) then { /* ... */ };

Detect an Undefined Variable

The isNil command, introduced in Armed Assault, allows to detect if a variable exists or not:

HelloThere = 42; isNil "HelloThere"; // false HelloThere = nil; isNil "HelloThere"; // true

isNil Workaround 1

SQS Syntax:

_nil = format ["%1", _undefinedVariable] ? (format ["%1", variableToTest] == _nil) : hint "variableToTest is nil"

SQF Syntax:

_nil = format ["%1", _undefinedVariable]; if (format ["%1", variableToTest] == _nil) then { hint "variableToTest is nil" };

isNil Workaround 2

The following information is obsolete as of Armed Assault. Reason: Armed Assault introduced isNil, and Arma 2 forbade undefined variables usage in script - see ArmA: Editing - Forward Compatibility.

The alternative way to check if a variable is undefined before isNil existence is that it silently fails any expression evaluations on it:

defined = false; if (var == var) then { defined = true; }; if (var != var) then { defined = true; }; if (!defined) then { // we know var is undefined here };

Type Inference

Suppose the variable a is undefined, and we set the variable b like so:

b = a + [];

The inferred type of b is now array - since b was the product result of an array add operation with a definite array ([]) and an unknown type (a)

b's string representation will now be "array", and b wil be considered an undefined array.