How to test if variable is assigned?

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

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

What about

int i;


Question by:baltmann

Expert Comment

ID: 9895490
LVL 19

Expert Comment

ID: 9895554
as far as i understood..

int i;
if (i!=null) // if the variable has been assigned

Author Comment

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;
Operator '==' cannot be applied to operands of type 'int' and '<null>'

LVL 20

Accepted Solution

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
  // ok

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

Assisted Solution

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

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

//your int has been set
//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.

Featured Post

Announcing the Most Valuable Experts of 2016

MVEs are more concerned with the satisfaction of those they help than with the considerable points they can earn. They are the types of people you feel privileged to call colleagues. Join us in honoring this amazing group of Experts.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Graphics 2 32
C# bracket error 3 35
VB.NET 2008 - SQL Timeout 9 34
VS2013 publish C# application Created folder -- where is it??? 10 27
Article by: Ivo
C# And Nullable Types Since 2.0 C# has Nullable(T) Generic Structure. The idea behind is to allow value type objects to have null values just like reference types have. This concerns scenarios where not all data sources have values (like a databa…
The article shows the basic steps of integrating an HTML theme template into an ASP.NET MVC project
Microsoft Active Directory, the widely used IT infrastructure, is known for its high risk of credential theft. The best way to test your Active Directory’s vulnerabilities to pass-the-ticket, pass-the-hash, privilege escalation, and malware attacks …
Nobody understands Phishing better than an anti-spam company. That’s why we are providing Phishing Awareness Training to our customers. According to a report by Verizon, only 3% of targeted users report malicious emails to management. With compan…

792 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question