Exception while accessing FileInfo Class

Question

I am trying to access all the files inside sub folders which are present inside a master folder, along with their last access times.

I am able to get all the files, the problem arises when I'm trying to get the last access times.

I receive the 'Object not set to an instance of an object' exception.

I am not able to see the anomaly in my code.

Below is the code:

public List<String> GetDirs(string Dir)
        {
            List<String> files = new List<String>();
            try
            {
                foreach (string f in Directory.GetFiles(Dir))
                {
                    files.Add(f);
                }
                foreach (string d in Directory.GetDirectories(Dir))
                {
                    files.AddRange(GetDirs(d));
                }
                int num=files.Count;
                FileInfo[] fileinfo=null;
                for (int i = 0; i < num; i++)
                {
                    fileinfo[i] = new FileInfo(files[i]);//Exception at this line of code

                }
                foreach(FileInfo xx in fileinfo)
                {
                    Response.Write(xx.LastWriteTime);
                }
              }
            catch (System.Exception excpt)
            {
                Response.Write(excpt.Message);
            }

            return files;
        }

The code is called as:

    string fullPath = @"D:\Main\Folder1";
    List<string> lst=GetDirs(fullPath);

The code is not complete at this time.

There are 3 text files inside Folder1, such as:

D:\Main\Folder1\a.txt

D:\Main\Folder1\bin\a1.txt

D:\Main\Folder1\SubFolder1\sa1.txt

I am trying to get the last access times for the above files too, but the exception doesn't permit to go further.

Sorry, but you have the debugger, probably the entire Visual Studio support, and you don't know the exactly line of the exception? — gustavodidomenico, Jun 12 '14 at 17:44
Well which line is throwing the exception, and what have you done to diagnose it? — Jon Skeet, Jun 12 '14 at 17:45
By inspection, `fileinfo[i]` is going to fail as `fileinfo` is null... How did you expect that to work? — Jon Skeet, Jun 12 '14 at 17:45
@JonSkeet fileinfo[0]=new FileInfo(D:\Main\Folder1\a.txt)..I think on the first iteration, the above line of code should arrive.. — Anurag, Jun 12 '14 at 17:47
@gustavodidomenico I have debugged and have pointed out the line of code which throws the exception. Have a look again to the question. — Anurag, Jun 12 '14 at 17:49
You must agree with me, that you could make things easier... — gustavodidomenico, Jun 12 '14 at 17:50
@gustavodidomenico I totally second your point. Next time onwards I will make the codes and comments pretty clearer. — Anurag, Jun 12 '14 at 17:51

D Stanley · Accepted Answer · 2014-06-12T17:55:17.793

It's pretty obvious here:

FileInfo[] fileinfo=null;   // <-- fileinfo is null
for (int i = 0; i < num; i++)
{
    fileinfo[i] = new FileInfo(files[i]);//Exception at this line of code
//   ^--- fileinfo is still null!
}

you are trying to use the indexer on a null reference to set a value. I think you want:

FileInfo[] fileinfo= new FileInfo[num];
for (int i = 0; i < num; i++)
{
    fileinfo[i] = new FileInfo(files[i]);//Exception at this line of code
}

or just

FileInfo[] fileinfo = files.Select(f => new FileInfo(f)).ToArray();

EDIT

After reading your comments, it seems that you think that FileInfo[] fileinfo=null; will initialize an array of null values (which is true in some languages, but not C#). In fact, it creates an array variable that is itself a null value. To initialize an array, you use the syntax FileInfo[] fileinfo=new FileInfo[size]; which will create an array of null values (more precisely, of the default value for FileInfo, which is null since it's a reference type).

score 0 · Answer 2 · answered Jun 12 '14 at 17:46

0

You are not initializing FileInfo[] fileinfo.

Fix: FileInfo[] fileInfo = new FileInfo[num]

answered Jun 12 '14 at 17:46

Victor Hurdugaci

28,177
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score 0 · Answer 3 · answered Jun 12 '14 at 19:51

Your code seems...a little complex...for what it does. Wouldn't it be a lot easier to let the framework do the work for you and say something like this:

public static IEnumerable<FileSystemInfo> ContentsOfDirectoryTreeRootedAt( string rootDirectory )
{
  DirectoryInfo root = new DirectoryInfo( rootDirectory ) ;
  if ( !root.Exists ) throw new DirectoryNotFoundException(rootDirectory) ;

  foreach( FileSystemInfo entry in root.EnumerateFileSystemInfos(null,SearchOption.AllDirectories) )
  {
    yield return entry ;
  }

}

Then you can invoke it along these lines:

foreach( FileInfo fi in ContentsOfDirectoryTreeRootedAt( @"C:\foo\bar" ).Where( x => x is FileInfo ).Cast<FileInfo>() )
{
  Console.Write( "FileName: {0}" , fi.FullName ) ;
  Console.Write( "\t" );
  Console.Write( "Last Updated: {1}" , fi.LastWriteTime ) ;
  Console.Write( "\t" );
  Console.Write( "Size: {0:0.0}kb" , (decimal)fi.Length / 1024m ) ;
  Console.WriteLine() ;
}

Exception while accessing FileInfo Class

3 Answers3