Variable Context Question

Question

In the following code snippet, if I leave out the line of code that is surrounded by the /////'s, I get an error that reads: "Use of unassigned local variable CurrentDate". It seems a bit silly for me to just give CurrentDate an arbitrary value, is there a better way around this?

DateTime CurrentDate;

///////////////////////////
CurrentDate = DateTime.Now;
///////////////////////////

if(1==1)
{
CurrentDate = DateTime.Now.AddDays(1);
}

if(CurrentDate == DateTime.Now)
{
...
}

Answer 1

Don't do if (1 == 1)?

Seriously though if the compiler is giving you this error it's usually either because your code is wrong or it's because it's too complex and could be better expressed in another way where you don't need to access possibly unassigned variables.

Can you come up with a real world example where you get this error where there isn't an obvious solution by making a simple refactoring? This would make your question more answerable.

Having said that if you do run into one of these situations there are a few other approaches you could use:

DateTime CurrentDate = DateTime.MaxValue;
DateTime CurrentDate = default(DateTime);
DateTime? CurrentDate = null;

I like the last option because it expresses what you mean - that you don't know the value. It makes the code a little more verbose though as you have an extra level of redirection every time you wish to access a value. You can use the time spent typing .Value to consider whether or not you have correctly handled the situation where it could be null.

Also: Have you considered that the value of DateTime.Now could change between the first and second calls? That final if statement looks like it won't do what you intended.

Answer 2

You could do this:

DateTime CurrentDate;


if(1==1)
{
CurrentDate = DateTime.Now.AddDays(1);
}
else
{
///////////////////////////
CurrentDate = DateTime.Now;
///////////////////////////
}

if(CurrentDate == DateTime.Now)
{
...
}

This will eliminate the compiler error.

NOTE: in VS2008 this will compile:

if(1==1)
{
CurrentDate = DateTime.Now.AddDays(1);
}
//else
//{
/////////////////////////////
//CurrentDate = DateTime.Now;
/////////////////////////////
//}

if(CurrentDate == DateTime.Now)
{
//
}

Answer 3

why dont just assigned directly

DateTime CurrentDate =  DateTime.Now; 

Answer 4

The example is a bit convoluted, but, no, there isn't a better way around that.

You have to assign a value to a variable heading into a conditional block, even if you are sure that the block will always execute (the 1=1 in your example)

However, I would recommend against DateTime.Now as the initialization value, because it by some mirracle, the block does not execute, the situation should be easily detectable, and DateTime.Now sound way more real than DateTime.MinValue

Answer 5

I always set my objects to null so that it throws a null reference exception if a value is not created. However as Hans pointed out null doesn't work in this situation because in their infinite wisdom Microsoft decided to make DateTime not nullable. As such I normally use DateTime.MinValue since it gives me a specific value to check for and other than time traveling will always be in the past unlike DateTime.MaxValue which is coming up here for some of you archaic 32bit peeps.

Example

DateTime CurrentDate;

///////////////////////////
CurrentDate = DateTime.MinValue;
///////////////////////////

if(1==1)
{
CurrentDate = DateTime.Now.AddDays(1);
}

if(CurrentDate == DateTime.Now)
{
...
}