c# foreach loop access variable

Question

I have the following problem: i have a string variable, which has to store a filepath. In a foreach loop i go through all files in a certain directory and im looking for the oldest, which is saved in that string variable. When the loop is finished i try to delete that file, but i get an error: Use of an unassigned local variable.

Here is the code:

DateTime min = DateTime.Now;
string[] fileNames = Directory.GetFiles(somePath);
string fileDelete;
int countFiles = fileNames.Length;
if (countfiles > 5)
{
    foreach (string someFile in fileNames)
    {
        FileInfo infoFile = new FileInfo(someFile);
        if (infoFile.CreationTime <= min)
        {
            min = infoFile.CreationTime;
            fileDelete = someFile;
        }   
    }
    File.Delete(fileDelete);
}

it says that the string fileDelete in File.Delete(fileDelete) has no value, but the fun thin is, when i give it a value at the beginning just like that:

string fileDelete = "blabla";

it works perfectly fine. This is just a snipped of the method in case you are wondering

When you do string fileDelete = "blabla";, the variable is no longer unassigned. Is countFiles bigger than 5? Does at least one file have a creation time before DateTime.Now? Your code does not guarantee that fileDelete is assigned, so it's going to go wrong at some point. — Bart van Nierop
– Bart van Nierop, Commented Jan 20, 2016 at 12:04
As others said, compiler can only work with variable when it is initialized explicitly. So just use string fileDelete = ""; — Fabjan
– Fabjan, Commented Jan 20, 2016 at 13:00
Thank you all for your awnsers. I understand the problem now. I just forgot that the compiler can not know that condition 2 is always met when condition 1 is (in my programm), and the compiler saw a case, where File.Delete will be executed without a value, even though this can not happen in my code. — sebastian
– sebastian, Commented Jan 20, 2016 at 13:44

Serve Laurijssen · Accepted Answer · 2016-01-20 12:03:47Z

3

in C# you have to initialise variables, otherwise you could pass garbage values to File.Delete.

I recommend using

string fileDelete = null; // or ""

and later check for that.

if (!string.IsNullOrEmpty(fileDelete))
{
  File.Delete(fileDelete);
}

answered Jan 20, 2016 at 12:03

Serve Laurijssen

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Comments

Andrey Korneyev · Accepted Answer · 2016-01-20 12:09:29Z

1

It works exactly as intended.

In C# local variables are not initialised automatically at declaration.

You're not assinging any value to the fileDelete when declaring it and assigning it only under some condition in your loop.

But you're trying to use its value outside this condition in loop, thus compiler can't deduce - will fileDelete has some value at runtime or not (if code under condition will not be executed - then fileDelete will has no value).

Thus compiler generates this error.

edited Jan 20, 2016 at 12:09

answered Jan 20, 2016 at 12:03

Andrey Korneyev

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1 Comment

sebastian Over a year ago

thats right thank you. I just forgot that the compiler can not know that condition 2 is always met when condition 1 is (in my programm).

Kapol · Accepted Answer · 2016-01-20 12:02:37Z

0

Imagine this scenario:

countFiles > 5 is True
infoFile for someFile is bigger than min

What value will fileDelete have when passed to File.Delete?

Answer: In such scenario fileDelete will be uninitialized, thus the error message.

answered Jan 20, 2016 at 12:02

Kapol

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1 Comment

sebastian Over a year ago

Thats 100% right. I just didn't see that case because it can not happen in my program, but of course the compiler thinks it could happen.

Community · Accepted Answer · 2017-05-23 12:07:28Z

0

You must initialize your variable. see at Why compile error "Use of unassigned local variable"?

edited May 23, 2017 at 12:07

CommunityBot

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answered Jan 20, 2016 at 12:11

Georgios Tsaprazlis

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Comments

Suvidha · Accepted Answer · 2016-01-20 12:23:50Z

0

Use this

DateTime min = DateTime.Now;
string[] fileNames = Directory.GetFiles(somePath);
string fileDelete;
int countFiles = fileNames.Length;
if (countfiles > 5)
{
    foreach (string someFile in fileNames)
    {
        FileInfo infoFile = new FileInfo(someFile);
        if (infoFile.CreationTime <= min)
        {
            min = infoFile.CreationTime;
            fileDelete = someFile;
            File.Delete(fileDelete);
        }   
    }

}

answered Jan 20, 2016 at 12:23

Suvidha

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2 Comments

Serve Laurijssen Over a year ago

this would make fileDelete redundant completely

sebastian Over a year ago

I didn't test this but i think this will just delete all files that are older than now. But i wanted to delete only the oldest file in a certain directory

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