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How to test if variable is assigned?

Posted on 2003-12-08
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Last Modified: 2008-03-06
System.DateTime d;

How do you test if the variable d has been assigned?

What about

int i;

?

0
Comment
Question by:baltmann
5 Comments
 
LVL 3

Expert Comment

by:monkesdb
ID: 9895490
eh?
0
 
LVL 19

Expert Comment

by:Desp
ID: 9895554
as far as i understood..

int i;
....
if (i!=null) // if the variable has been assigned
{
...
}
0
 

Author Comment

by:baltmann
ID: 9895811
The compile errors are:

with DateTime:

System.DateTime dt ;
if(dt != null)
...
Operator '!=' cannot be applied to operands of type 'System.DateTime' and '<null>'

with int:
int i;
if(i==null){i=0;}
...
Operator '==' cannot be applied to operands of type 'int' and '<null>'

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LVL 20

Accepted Solution

by:
TheAvenger earned 50 total points
ID: 9896285
An object is checked with o != null. Objects are strings, forms, arraylists, etc. However DateTime and int are value types, which means they cannot be compared to null.

So you have to implement your own logic. For example if you need only positive numbers you can do like this:

int i = -1;
...
if (i < 0)
  // still no real value
else
  // ok

For DateTime you can make:
DateTime dt = DateTime.MinValue;
...
if (dt == DateTime.MinValue)
  // still no real value
else
  // ok
0
 
LVL 7

Assisted Solution

by:jj819430
jj819430 earned 50 total points
ID: 9897533
int i;
bool iSet = false;

// whenever you set i, set iSet = true;

if(iSet)
{
//your int has been set
}
if(!iSet)
{
//your int has not been set
}

All the others were just as valid a way of doing this, because they do not require the added overhead. I  like this approach only because it doesn't limit the functionality of the int. If you will only be using positive or only be using negative numbers I would suggest you use "TheAvenger"'s approach for the speed. If you need both Positive and Negative integer values, then this may be your best approach.
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