# Function Reference

# IsDeclared

Check if a variable has been declared.

IsDeclared ( expression )

## Parameters

expression | string representing name of the variable to be checked.

## Return Value

Success: | $DECLARED_GLOBAL (1) for Global variable or variable declared outside functions.
Special: | $DECLARED_LOCAL (-1) for Local variable.
Failure: | $DECLARED_UNKNOWN (0) when no variable can be found.

Constants are defined in AutoItConstants.au3

## Remarks

If there is a need to use IsDeclared() to check that a variable exists, then in most situations Assign() should be used to create/write to the variable and Eval() should be used to read from the variable.

## Related

Assign, Eval

## Example

    #include <MsgBoxConstants.au3>

    ; Check if the variable $vVar is declared. As the variable isn't will display the error message.
    If Not IsDeclared("vVar") Then
        MsgBox($MB_SYSTEMMODAL, "", "The variable $vVar is not declared.")

        Local $vVar = 0 ; Initialize the variable $vVar with data.
        If IsDeclared("vVar") Then ; Check if the variable $vVar is declared.
            MsgBox($MB_SYSTEMMODAL, "", "The variable $vVar is declared.")
        Else
            MsgBox($MB_SYSTEMMODAL, "", "The variable $vVar is not declared.")
        EndIf
    EndIf