how to check if a variable exists or isset in asp?

how can i check to see if a variable exists? or whether it has been set in asp?
thanks

try to use:

if not variable = null then ....

i tried:

if NOT isnull(variable) then

but it doesnt work

I don't think there is a similar VBScript function to isset, at least not one that comes to mind. I generally use Option Explicit in asp code so there aren't any undefined variables in code.

In ASP, I typically use Len(variable)>2, or any number safe enough to make assumptions on. Typically, if a recordset or form variable is undefined, this will return 0, where in PHP, an error is thrown, thus the need for isset.

Hope that helps.

so try len(var)>0

what ive got working is to find whether a form has been posted
in php i have used:
isset($_POST)
and
$_SERVER['REQUEST_METHOD'] == "post"

but i also use isset alot in php, to check if a variable has been set, if not then either create it or do something

what will Option Explicit do if i used it?
the: NOT isnull(var) option doesnt seem to work as an asp alternative to isset but could this be due to not setting Option Explicit?

I've had no luck with the isnull function in the past. ASP seems to have strange ideas about the length and type of a variable pulled from a database.

Option Explicit requires that all variables be defined before they are called by using Dim. Normally ASP does not require this, and many lazy coders (me included) don't use it so that they don't have to write out every variable that they're going to use in the page.
Info on Option Explicit

To check whether a form has been posted, you can either do
If Len(Request.Form("fieldName")>1 Then
as long as that fieldName corresponds to a field you are certain will be populated.
Or, add a senseless URL variable to the form's action, like:
<form action="post.asp?submit=1">
Then:
If Request.QueryString("submit")=1 Then

Hope that helps.

if Request.ServerVariables("REQUEST_METHOD") = "POST" then
if not Request.Form("control_name") = "" then
..........

I think ISEMPTY can be used

Cut and paste from the quote in ur ASP page and check what is the result


ISEMPTY can be used as follows

I'm having the same problem with an Isset or similar function.

Basically I'm trying to access a database, and if the select comes back with nothing then print one thing, otherwise print something else....

So Was there any conclusion to this thread then?

I usually use this:

If Len(yourRS("yourField"))>1 Then
....DO SOMETHING....
Else
....DO SOMETHING ELSE....
End If

Does that not work?

You can try use this code:

If TypeName(var) <> "Nothing" Then
....DO SOMETHING....
Else
....DO SOMETHING ELSE....
End If

Thanks for the reply, but you may not have noticed this is a very old thread Also, I think the Nothing keyword only applies to object variables.