C#: Using StreamReader to read line from txt file, but Peek() return -1 even there are a lot of lines left

Question

I use Peek() method of StreamReader to check whether there are more lines need to be processed. There are more than 1000 lines in my file, but Peek() suddenly return -1 when it reachs line#750. I checked but seems no differences between line#750 and #751. Even I deleted line#750 and 751, it will still break up at other line.

Below are my codes for your information:

try
{
    String ftpserver = ftp + filename;
    reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri(ftpserver));
    reqFTP.UsePassive = false;
    reqFTP.UseBinary = true;
    reqFTP.Proxy = null;
    reqFTP.Credentials = new NetworkCredential(username, password);

    reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
    response = (FtpWebResponse)reqFTP.GetResponse();
    stream = response.GetResponseStream();
    reader = new StreamReader(stream, ConfigHelper.MyEncoding);
    while (reader.Peek() > -1)
    {
        string x = reader.ReadLine();
        if (x != null)
        {
          //.......
         }
    }
}
catch (Exception ex)
{
}
finally
{
    if (reader != null)
        reader.Close();
    if (response != null)
        response.Close();
}

I tried while ((x = reader.ReadLine()) != null), but an exception of "Cannot access a disposed object" was thrown out.

Finally I figured it out by using: while (stream.CanRead && (x = reader.ReadLine()) != null)

Answer 1

While it doesn't explain what's going on, I'd personally avoid using Peek. I'd use:

string line;
while ((line = reader.ReadLine()) != null)
{
    // Use the line
}

That way you're only reading in one place. It somehow feels more sane than checking whether or not you can read, and then reading.

You can also write a method to create an IEnumerable<string> from a TextReader (or from a Func<TextReader>, or a filename) which can make all of this more pleasant. If you're just reading a file and you're using .NET 4, then File.ReadLines is already built-in.

EDIT: Here's one reason you may be getting -1, from the docs of StreamReader.Peek:

An integer representing the next character to be read, or -1 if there are no characters to be read or if the stream does not support seeking.

Does your stream support seeking?

Answer 2

I'm not sure why Peek Method returns -1 in your case, but the usual way to read lines with the StreamReader Class to the end of the file is to repeatedly call the ReadLine Method until null is returned:

string line;
while ((line = reader.ReadLine()) != null)
{
    Console.WriteLine(line);
}