Override ReadLine StreamReader Method

Question

I am trying to override the StreamReader ReadLine method, but I can hardly do it due to the inability to access some private variables. Is this possible, or should I just write my own StreamReader class?

Answer 1

Assuming you want your custom StreamReader to be used wherever TextReader can be used, there are usually two options.

• Inherit from StreamReader and redefine functions that you want to work differently. In your case, it will be StreamReader.ReadLine.

• Inherit from TextReader and fully realize the reader’s capabilities according to your requirements.

Note. For option 2 above, you can save the internal reference to the StreamReader instance and delegate all functions to the internal instance, except for the part of the functionality that you want to replace. In my opinion, this is just a detail of the implementation of option 2, and not the third option.

Based on your question, I assume that you tried option 1 and found that redefining StreamReader.ReadLine is quite difficult because you cannot access the internal functions of the class. Well, for StreamReader you are lucky and can achieve this without having access to the internal StreamReader implementation.

Here is a simple example:

Disclaimer: ReadLine() implementation is intended for demonstration purposes and is not intended for reliable or complete implementation.

 class CustomStreamReader : StreamReader { public CustomStreamReader(Stream stream) : base(stream) { } public override string ReadLine() { int c; c = Read(); if (c == -1) { return null; } StringBuilder sb = new StringBuilder(); do { char ch = (char)c; if (ch == ',') { return sb.ToString(); } else { sb.Append(ch); } } while ((c = Read()) != -1); return sb.ToString(); } } 

You will notice that I just used the StreamReader.Read () method to read the characters from the stream. Although it is definitely less for the formant that works directly with internal buffers, the Read() method uses internal buffering, so it should bring pretty good performance, but it should be checked for confirmation.

For fun, here is an example of option 2. I used the encapsulated StreamReader to reduce the actual code, this is not verified at all.

 class EncapsulatedReader : TextReader { private StreamReader _reader; public EncapsulatedReader(Stream stream) { _reader = new StreamReader(stream); } public Stream BaseStream { get { return _reader.BaseStream; } } public override string ReadLine() { int c; c = Read(); if (c == -1) { return null; } StringBuilder sb = new StringBuilder(); do { char ch = (char)c; if (ch == ',') { return sb.ToString(); } else { sb.Append(ch); } } while ((c = Read()) != -1); return sb.ToString(); } protected override void Dispose(bool disposing) { if (disposing) { _reader.Close(); } base.Dispose(disposing); } public override int Peek() { return _reader.Peek(); } public override int Read() { return _reader.Read(); } public override int Read(char[] buffer, int index, int count) { return _reader.Read(buffer, index, count); } public override int ReadBlock(char[] buffer, int index, int count) { return _reader.ReadBlock(buffer, index, count); } public override string ReadToEnd() { return _reader.ReadToEnd(); } public override void Close() { _reader.Close(); base.Close(); } } 

Answer 2

Try it, I wrote it because I have a very big '|' which have \ r \ n inside some columns, and I needed to use \ r \ n as the end of the line separator. I tried to import some files using SSIS packages, but due to some corrupted data in the files that I failed. The file was more than 5 GB, so it was too large to open and manually fix. I found the answer by looking at a lot of forums to understand how streams work, and eventually came up with a solution that reads every character in the file and splashes the line based on the definitions I added to it. this is for use in a command line application, bundled with :). Hope this helps some other people, I have not found a solution like him anywhere else, although the ideas were inspired by this forum and others. This will not fix the files that it only shares them ... keep in mind that this is still ongoing work :).

     class program
     {
         static long _fileposition = 0;

         static void Main (string [] args)
         {

             // Check information passed in
             if (args.Any ())
             {
                 if (args [0] == "/?")
                 {
                     var message = "Splits a file into smaller pieces";
                     message + = "\ n";
                     message + = "\ n";
                     message + = "SplitFile [sourceFileName] [destinationFileName] [RowBatchAmount] [FirstRowHasHeader]";
                     message + = "\ n";
                     message + = "\ n";
                     message + = "[sourceFileName] (STRING) required";
                     message + = "\ n";
                     message + = "[destinationFileName] (STRING) will default to the same location as the sourceFileName";
                     message + = "\ n";
                     message + = "[RowBatchAmount] (INT) will create files that have this many rows";
                     message + = "\ n";
                     message + = "[FirstRowHasHeader] (True / False) Will Add Header Row to each new file";
                     Console.WriteLine (message);
                 }
                 else
                 {
                     string sourceFileName = args [0];
                     string destFileLocation = args.Count ()> = 2?  args [1]: sourceFileName.Substring (0, sourceFileName.LastIndexOf ("\\"));
                     int RowCount = args.Count ()> = 3?  int.Parse (args [2]): 500000;
                     bool FirstRowHasHeader = true;
                     FirstRowHasHeader = args.Count ()! = 4 ||  bool.Parse (args [3]);

                     // Create Directory If Needed
                     if (! Directory.Exists (destFileLocation))
                     {
                         Directory.CreateDirectory (destFileLocation);
                     }

                     string line = "";
                     int linecount = 0;
                     int FileNum = 1;
                     string newFileName = Path.Combine (destFileLocation, Path.GetFileNameWithoutExtension (sourceFileName));
                     newFileName + = FileNum + Path.GetExtension (sourceFileName);

                     // Always add Header Line
                     string HeaderLine = GetLine (sourceFileName, _fileposition);
                     int HeaderCount = HeaderLine.Split ('|'). Count ();

                     do
                     {
                         // Add Header Line
                         if ((linecount == 0 & FirstRowHasHeader) | (_fileposition == 1 &! FirstRowHasHeader))
                         {
                             using (FileStream NewFile = new FileStream (newFileName, FileMode.Append))
                             {
                                 System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding ();
                                 Byte [] bytes = encoding.GetBytes (HeaderLine);
                                 int length = encoding.GetByteCount (HeaderLine);
                                 NewFile.Write (bytes, 0, length);
                             }
                         }

                         // Evaluate Line
                         line = GetLine (sourceFileName, _fileposition, HeaderCount);

                         if (line == null) continue;

                         // Create File if it doesn't exist and write to it
                         using (FileStream NewFile = new FileStream (newFileName, FileMode.Append))
                         {
                             System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding ();
                             Byte [] bytes = encoding.GetBytes (line);
                             int length = encoding.GetByteCount (line);
                             NewFile.Write (bytes, 0, length);
                         }

                         // Add to the line count
                         linecount ++;

                         // Create new FileName if needed
                         if (linecount == RowCount)
                         {
                             FileNum ++;
                             // Create a new sub File, and read into it
                             newFileName = Path.Combine (destFileLocation, Path.GetFileNameWithoutExtension (sourceFileName));
                             newFileName + = FileNum + Path.GetExtension (sourceFileName);
                             linecount = 0;
                         }
                     } while (line! = null);
                 }
             }
             else
             {
                 Console.WriteLine ("You must provide sourcefile!");
                 Console.WriteLine ("use /? For help");
             }
         }

         static string GetLine (string sourceFileName, long position, int NumberOfColumns = 0)
         {
             byte [] buffer = new byte [65536];
             var builder = new StringBuilder ();
             var finishedline = false;

             using (Stream source = File.OpenRead (sourceFileName))
             {
                 source.Position = position;
                 var crlf = "\ r \ n";
                 var lf = "\ n";
                 var length = source.Length;

                 while (source.Position = 0 & finishedline == false & _fileposition = NumberOfColumns) |  NumberOfColumns == 0)
                                             {
                                                 // Remove all Control Line Feeds before the end of the line.
                                                 builder = builder.Replace (crlf, lf);

                                                 // Add Final Control Line Feed
                                                 var x = (char) NewLine.Read ();
                                                 builder.Append (x);
                                                 finishedline = true;
                                                 _fileposition ++;
                                                 continue;
                                             }
                                         }

                                         break;
                                     }
                                 default:
                                     builder.Append (c);
                                     break;
                             }
                         }
                     }
                     break;
                 }
             }

             return (builder.ToString () == ""? null: builder.ToString ());
         }
     }

Links: http://social.msdn.microsoft.com/forums/en-US/csharpgeneral/thread/b0d4cba1-471a-4260-94c1-fddd4244fa23/

this helped me the most: https://stackoverflow.com/a/312969/

Answer 3

this class can help you

 public class MyStreamReader : System.IO.StreamReader { public MyStreamReader(string path) : base(path) { } public override string ReadLine() { string result = string.Empty; int b = base.Read(); while ((b != (int)',') && (b > 0)) { result += this.CurrentEncoding.GetString(new byte[] { (byte)b }); b = base.Read(); } return result; } }