Question

I have a function like this:

   List<float> myList = new List(float);

     public void numbers(string filename)
    {
        string input;
        float number;

        if (System.IO.File.Exists(filename) == true)
        {
            System.IO.StreamReader objectReader;
            objectReader = new System.IO.StreamReader(filename);

            while ((input = objectReader.ReadLine()) != null)
            {
                number = Convert.ToSingle(input);
                myList.Add(number);
            }
            objectReader.Close();
        }
        else
        {
            MessageBox.Show("No Such File" + filename);
        }
    }

Where Im trying to add numbers (floats) from a text file into a List. But I keep getting errors saying wrong format. The numbers in the text file are one number per line…any help?

Answer 1

Your code worked fine for me except for the case of a newline (and of course for entries that were not numbers at all)

Here is a version that should work for you, using a tryParse to check if each line can convert to a single):

    public void Numbers(string filename)
    {
        List<float> myList = new List<float>();     

        string input;

        if (System.IO.File.Exists(filename) == true)
        {
            System.IO.StreamReader objectReader;
            objectReader = new System.IO.StreamReader(filename);
            while ((input = objectReader.ReadLine()) != null)
            {
                Single output;
                if (Single.TryParse(input, out output ))
                {
                    myList.Add(output);
                }
                else
                {
                   // Huh? Should this happen, maybe some logging can go here to track down why you couldn't just use the .Convert()
                }
            }
            objectReader.Close();

        }
        else
        {
            MessageBox.Show("No Such File" + filename);
        }
    }

As Mike C rightly points out, this could be potentially risky – swallowing good data that has been corrupted by the output process. The tryParse method returns false when it fails so you could add in an else branch and some logging to check just what is causing the failures and see if there is another bug floating around that can be corrected.