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copied!<p>I can't remember where this came from exactly, but it has worked pretty well for me in the past.</p> <p>Replaced reader with writer:</p> <pre><code>/// <summary> /// A stream writer that allows its current position to be recorded and /// changed. This is not generally possible for stream writers, because /// of the use buffered reads. /// This writer can be used only for text content. Theoretically it can /// process any encoding, but was checked only for ANSI and UTF8 If you /// want to use this class with any other encoding, please check it. /// NOT SAFE FOR ASYNC WRITES. /// </summary> public class PositionableStreamWriter : StreamWriter { /// <summary> /// Out best guess counted position. /// </summary> private long _position; /// <summary> /// Guards against e.g. calling "Write(char[] buffer, int index, int count)" /// as part of the implementation of "Write(string value)", which would cause /// double counting. /// </summary> private bool _guardRecursion; public PositionableStreamWriter(string fileName, bool append, Encoding enc) : base(fileName, append, enc) { CommonConstruct(); } public PositionableStreamWriter(Stream stream, Encoding enc) : base(stream, enc) { CommonConstruct(); } /// <summary> /// Encoding can really haven't preamble /// </summary> private bool CheckPreamble(long lengthBeforeFlush) { byte[] preamble = this.Encoding.GetPreamble(); if (this.BaseStream.Length >= preamble.Length) { if (lengthBeforeFlush == 0) return true; else // we would love to read, but base stream is write-only. return true; // just assume a preamble is there. } return false; } /// <summary> /// Use this property to get and set real position in file. /// Position in BaseStream can be not right. /// </summary> public long Position { get { return _position; } set { this.Flush(); ((Stream)base.BaseStream).Seek(value, SeekOrigin.Begin); _position = value; } } public override void Write(char[] buffer) { if (buffer != null && !_guardRecursion) _position += Encoding.GetByteCount(buffer); CallBase(() => base.Write(buffer)); } public override void Write(char[] buffer, int index, int count) { if (buffer != null && !_guardRecursion) _position += Encoding.GetByteCount(buffer, index, count); CallBase(() => base.Write(buffer, index, count)); } public override void Write(string value) { if (value != null && !_guardRecursion) _position += Encoding.GetByteCount(value); CallBase(() => base.Write(value)); } public override void WriteLine() { if (!_guardRecursion) _position += Encoding.GetByteCount(NewLine); CallBase(() => base.WriteLine()); } public override void WriteLine(char[] buffer) { if (buffer != null && !_guardRecursion) _position += Encoding.GetByteCount(buffer) + Encoding.GetByteCount(NewLine); CallBase(() => base.WriteLine(buffer)); } public override void WriteLine(char[] buffer, int index, int count) { if (buffer != null && !_guardRecursion) _position += Encoding.GetByteCount(buffer, index, count) + Encoding.GetByteCount(NewLine); CallBase(() => base.WriteLine(buffer, index, count)); } public override void WriteLine(string value) { if (value != null && !_guardRecursion) _position += Encoding.GetByteCount(value) + Encoding.GetByteCount(NewLine); CallBase(() => base.WriteLine(value)); } private void CallBase(Action callBase) { if (_guardRecursion == true) callBase(); else { try { _guardRecursion = true; callBase(); } finally { _guardRecursion = false; } } } private void CommonConstruct() { var lenghtAtConstruction = BaseStream.Length; if (lenghtAtConstruction == 0) Flush(); // this should force writing the preamble if a preamble is being written. //we need to add length of symbol which is in begin of file and describes encoding of file if (CheckPreamble(lenghtAtConstruction)) { _position = this.Encoding.GetPreamble().Length; } } } </code></pre> <p>Usage:</p> <pre><code>class Program { static void Main(string[] args) { var pos = new List<long>(); using (var writer = new PositionableStreamWriter("tst.txt", false, Encoding.Unicode)) { pos.Add(writer.Position); writer.Write("abcde"); pos.Add(writer.Position); writer.WriteLine("Nope"); pos.Add(writer.Position); writer.WriteLine("Something"); pos.Add(writer.Position); writer.WriteLine("Another thing"); pos.Add(writer.Position); } using (var stream = File.Open("tst.txt", FileMode.Open)) using (var reader = new BinaryReader(stream)) { for (int i = 0; i < pos.Count - 1; i++) { stream.Position = pos[i]; var len = (int)(pos[i + 1] - pos[i]); var buf = reader.ReadBytes(len); Console.Write(Encoding.Unicode.GetString(buf)); } } } } </code></pre>

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