I'm confused about why this object is null

[SlurrerOfSpeech]

I have a class like

    public class FriendList
    {
        public Dictionary<string, int> names { get; set; } // List of friends names and number of occurrences (in case two or more friends have the same name)
        public DateTime timestamp { get; set; } // date/time on the data file

        public static FriendList operator / ( FriendList first, FriendList second )
        {
            // Returns a FriendList of every friend in first but not second, with the timestamp
            // of the returned object being an arbitrary value. 
            FriendList firstNotSecond = new FriendList();
            foreach ( KeyValuePair<string,int> thisName in first.names  )
            {
                int secondNum = second.names.ContainsKey(thisName.Key) ? second.names[thisName.Key] : 0;
                if ( thisName.Value > secondNum )
                {
                    firstNotSecond.names[thisName.Key] = thisName.Value - secondNum;
                }
            }
            return firstNotSecond;          
        }

        public void PrintInfo ( )
        {
            Console.WriteLine("Friends from list timestamped with {0}", this.timestamp.ToString());
            foreach ( KeyValuePair<string, int> thisFriend in this.names )
            {
                Console.WriteLine("\t\t{0} ({1})", thisFriend.Key, thisFriend.Value);
            }
        }

        public int CountFriends ( )
        {
            int count = 0;
            foreach ( KeyValuePair<string, int> namein this.names )
            {
                count += name.Value;
            }
            return count;
        }

    }

but when I use that class in the following procedure

        private void BuildFriendHistory ( )
        {
            // Takes all text files currently in the Data folder
            // and extracts their friends lists into a List<FriendList>.
            // Prints any error encountered along the way.
            this._fhist = new List<FriendList>();
            foreach ( string thisFilePath in Directory.GetFiles(this._datadir) )
            {
                FriendList flist = new FriendList();
                string line;
                System.IO.StreamReader file = new System.IO.StreamReader(thisFilePath);
                while ( (line = file.ReadLine()) != null )
                {
                    int k = line.LastIndexOf(' ');
                    flist.names[line.Substring(0, k)] = Int32.Parse(line.Substring(k + 1));
                }
                this._fhist.Add(flist);
            }
        }

I'm getting a NullReferenceException on the line

flist.names[line.Substring(0, k)] = Int32.Parse(line.Substring(k + 1))

and I know (because I've stepped through and checked) that

line.Substring(0, k)

and

Int32.Parse(line.Substring(k + 1))

are not NULL. Therefore NULL is some part of

flist.names

and I'm wondering if you can help me figure out why.

 

[SlurrerOfSpeech]

Mods, you can remove this thread. I figured out my problem (Needed to create a constructor for FriendList objects and in that constructor intialize this.names = new Doctionary<string,int> () )

 

[Mark44]

while ( (line = file.ReadLine()) != null )
{
      int k = line.LastIndexOf(' ');
      flist.names[line.Substring(0, k)] = Int32.Parse(line.Substring(k + 1));
}
this._fhist.Add(flist);

Either flist is null or flist.names is null. Before drilling down to flist.names[line.Substring(0, k)], you should do some sanity check to make sure that neither of this is null. Nowhere in the code you posted did I see anything where flist is initialized, which you're probably already figured out.

BTW, just because a problem gets solved, we don't automatically delete a thread.

 

[SlurrerOfSpeech]

Either flist is null or flist.names is null. Before drilling down to flist.names[line.Substring(0, k)], you should do some sanity check to make sure that neither of this is null. Nowhere in the code you posted did I see anything where flist is initialized, which you're probably already figured out.

I thought that if you have a class like

public class MyClass
{
    SomeType MyField1 { get; set; }
    SomeOtherType MyField2 { get; set; }
}

then both fields are implicitely newed when creating a new MyClass.

 

[Mark44]

I thought that if you have a class like

public class MyClass
{
    SomeType MyField1 { get; set; }
    SomeOtherType MyField2 { get; set; }
}

then both fields are implicitely newed when creating a new MyClass.

Your code is C#, right? Assuming you have a constructor for MyClass, space is allocated for the data members of MyClass, but unless the constructor initializes these members explicitly they wil be initialized to 0 in some form, for numbers, and null if they are objects of some kind.

 

[SlurrerOfSpeech]

Your code is C#, right? Assuming you have a constructor for MyClass, space is allocated for the data members of MyClass, but unless the constructor initializes these members explicitly they wil be initialized to 0 in some form, for numbers, and null if they are objects of some kind.

Got it. Thanks!