Quote:
Without creating it if not?
Absolutely not^.
Since the ByRef parameter of VarExist cannot be omitted, the only way to call it is with a variable which already exists. VarExist will return 0 if the variable either has never been allocated a block of memory, or
has been allocated a block of memory but it has since been freed. For instance:
Code:
MsgBox % varExist(var)
; Initialize the variable. No memory needs to be allocated for zero-length values.
var := ""
MsgBox % varExist(var)
; VarSetCapacity giveth memory.
VarSetCapacity(var, 64)
MsgBox % varExist(var)
; VarSetCapacity taketh memory away.
VarSetCapacity(var, 0)
MsgBox % varExist(var)
varExist(ByRef v) { ; Requires 1.0.46+
return &v = &n ? 0 : v = "" ? 2 : 1
}
As documented, any non-dynamic reference to a variable creates the variable the moment the script starts. Using
n:="var" and
%n% in the above example does not change the results, since evaluating
%n% in an expression causes
var to be created. However, this does not apply to input variables. You may confirm by using ListVars:
Code:
n = var
; The following is essentially a command with a single InputVar arg:
if %n% !=
MsgBox
ListVars
MsgBox %n% does not exist.
; Simple assignments are optimised by replacing the expression with an InputVar:
_ := %n%
ListVars
MsgBox %n% does not exist.
; Expression:
_ := (%n%)
ListVars
MsgBox %n% exists.
Sometimes it is important to check for a dynamic variable without creating it, since each variable "permanently" consumes at least
sizeof(Var) bytes. As of v1.0.48, that's only 28 bytes, but it can add up. Usually it is sufficient to compare it to an empty value using a Traditional-If as demonstrated above. Note however the following may not work as expected (it depends on what you expect):
Code:
n = var
If %n%
MsgBox, For backwards-compatibility, 'If %n%' is equivalent to 'If n'.
^ It isn't possible to exclusively check whether a variable exists, but it is possible to check whether a non-empty, non-zero variable exists. In other words, there's no way to distinguish between a variable which doesn't exist and a variable which has no memory allocated to it - unless you count ListVars, but even that isn't fool-proof.
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I also get 2 in the last place. 