null empty "" 0 ......

[razaqad]

what is the difference between null , "" , empty, nothing etc.

how to reset variables (string, integers, dates etc)

eg:

dim abc as string

abc = "This is a string variable"

abc = ?? empty or "" , null , or what

 

[pono1]

It's a little confusing... But you can think of it this way: A string value in an Access table can be one of three types.

1. Length (my term), manifested many ways: "hello", "999-99-999Y", "Larry66", "etc"

2. Zero Length, manifested one way: ""

3. Null, manifested one way:

Null is neither a zero length string (ZLS) nor a string with length. Null is a type (or state, if you like) of a value. You can effectively stop Access tables from using Null by setting a field's Allow Zero Length and Required properties to Yes.

Regards,
Tim

PS. I'll let somebody else tackle objects and Nothing.

 

[razaqad]

so what are the values for different types of variables which have not yet been initialized

 

[Bat17]

Null is Access way of saying "I have no idea what this is"

so if you add some thing to a Null you still get Null, if you add to an empty string or 0 you get an answer

Null + "ABC" = Null
"" + "ABC" = "ABC"

you cant compare to a Null either because Access has no idea what it is.

if myVar = Null Then < this will give an error
if isNull(myVar) Then <Correct way to test for Nulls

Nothing works with the Set command and free's up memory

Set rst = CurrentDb.OpenRecordset(strSQL) < Allocates memory

Set rst = Nothing < frees it up agin

Hope that makes some sort of sense

Peter

 

[pono1]

so what are the values for different types of variables which have not yet been initialized

You can use a stop statement (or a breakpoint) as well as the Locals Window to find out (see attached pic).

Regards,
Tim