Question

大家好我需要做的是跟踪我从流阅读器中读取的行的位置当我说reader.ReadLine()我需要知道该行在文件中的位置时我也想要然后能够从我之前跟踪过的位置读取文件。

这可能吗？如果是这样，请协助。

非常感谢帮助

提前致谢。

Answer 1

您可以采取以下三种方式之一：

1）编写自己的StreamReader。这是一个很好的起点：How to know position(linenumber) of a streamreader in a textfile?

2）StreamReader类有两个非常重要但私有的变量，称为charPos和charLen，它们在查找实际的“读取”位置时需要，而不仅仅是流的底层位置。您可以使用反射来获取建议值here

的值

Int32 charpos = (Int32) s.GetType().InvokeMember("charPos", 
BindingFlags.DeclaredOnly | 
BindingFlags.Public | BindingFlags.NonPublic | 
BindingFlags.Instance | BindingFlags.GetField
 ,null, s, null); 

Int32 charlen= (Int32) s.GetType().InvokeMember("charLen", 
BindingFlags.DeclaredOnly | 
BindingFlags.Public | BindingFlags.NonPublic | 
BindingFlags.Instance | BindingFlags.GetField
 ,null, s, null);

return (Int32)s.BaseStream.Position-charlen+charpos;

3）只需将整个文件读入字符串数组即可。像这样：

char[] CRLF = new char[2] { '\n', '\r' };
TextReader tr = File.OpenText("some path to file");
string[] fileLines = tr.ReadToEnd().Split(CRLF);

另一种可能性（与＃3相同）是读取行并将行存储在数组中。如果要读取前一行，只需使用数组。

Answer 2

也许这可以帮到你

  public class StreamLineReader : IDisposable
    {
        const int BufferLength = 1024;

        Stream _Base;
        int _Read = 0, _Index = 0;
        byte[] _Bff = new byte[BufferLength];

        long _CurrentPosition = 0;
        int _CurrentLine = 0;

        /// <summary>
        /// CurrentLine number
        /// </summary>
        public long CurrentPosition { get { return _CurrentPosition; } }
        /// <summary>
        /// CurrentLine number
        /// </summary>
        public int CurrentLine { get { return _CurrentLine; } }
        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="stream">Stream</param>
        public StreamLineReader(Stream stream) { _Base = stream; }
        /// <summary>
        /// Count lines and goto line number
        /// </summary>
        /// <param name="goToLine">Goto Line number</param>
        /// <returns>Return true if goTo sucessfully</returns>
        public bool GoToLine(int goToLine) { return IGetCount(goToLine, true) == goToLine; }
        /// <summary>
        /// Count lines and goto line number
        /// </summary>
        /// <param name="goToLine">Goto Line number</param>
        /// <returns>Return the Count of lines</returns>
        public int GetCount(int goToLine) { return IGetCount(goToLine, false); }
        /// <summary>
        /// Internal method for goto&Count
        /// </summary>
        /// <param name="goToLine">Goto Line number</param>
        /// <param name="stopWhenLine">Stop when found the selected line number</param>
        /// <returns>Return the Count of lines</returns>
        int IGetCount(int goToLine, bool stopWhenLine)
        {
            _Base.Seek(0, SeekOrigin.Begin);
            _CurrentPosition = 0;
            _CurrentLine = 0;
            _Index = 0;
            _Read = 0;

            long savePosition = _Base.Length;

            do
            {
                if (_CurrentLine == goToLine)
                {
                    savePosition = _CurrentPosition;
                    if (stopWhenLine) return _CurrentLine;
                }
            }
            while (ReadLine() != null);

            // GoToPosition

            int count = _CurrentLine;

            _CurrentLine = goToLine;
            _Base.Seek(savePosition, SeekOrigin.Begin);

            return count;
        }
        /// <summary>
        /// Read Line
        /// </summary>
        /// <returns></returns>
        public string ReadLine()
        {
            bool found = false;

            StringBuilder sb = new StringBuilder();
            while (!found)
            {
                if (_Read <= 0)
                {
                    // Read next block
                    _Index = 0;
                    _Read = _Base.Read(_Bff, 0, BufferLength);
                    if (_Read == 0)
                    {
                        if (sb.Length > 0) break;
                        return null;
                    }
                }

                for (int max = _Index + _Read; _Index < max; )
                {
                    char ch = (char)_Bff[_Index];
                    _Read--; _Index++;
                    _CurrentPosition++;

                    if (ch == '\0' || ch == '\n')
                    {
                        found = true;
                        break;
                    }
                    else if (ch == '\r') continue;
                    else sb.Append(ch);
                }
            }

            _CurrentLine++;
            return sb.ToString();
        }
        /// <summary>
        /// Free resources
        /// </summary>
        public void Dispose()
        {
            if (_Base != null)
            {
                _Base.Close();
                _Base.Dispose();
                _Base = null;
            }
        }
    }

使用：

 using (StreamLineReader st = new StreamLineReader(File.OpenRead("E:\\log.txt")))
        {
            bool ok = st.GoToLine(1);
            int count= st.GetCount(0);

            string w0 = st.ReadLine();
            string w1 = st.ReadLine();
            string w2 = st.ReadLine();
            string w3 = st.ReadLine();
        }

Answer 3

跟踪实际StreamReader的位置（以字节为单位）：

private readonly static FieldInfo charPosField = typeof(StreamReader).GetField("charPos", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly);
private readonly static FieldInfo charLenField = typeof(StreamReader).GetField("charLen", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly);
private readonly static FieldInfo charBufferField = typeof(StreamReader).GetField("charBuffer", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly);

static long ActualPosition(StreamReader reader)
{
    var charBuffer = (char[])charBufferField.GetValue(reader);
    int charLen = (int)charLenField.GetValue(reader);
    int charPos = (int)charPosField.GetValue(reader);

    return reader.BaseStream.Position - reader.CurrentEncoding.GetByteCount(charBuffer, charPos, charLen-charPos);
}

不客气。

Answer 4

您可以使用的另一种模式是要更改位置时使用新的StreamReader。这适用于任何版本的.net，并且不需要太多代码。

using var stream = File.Open("file.txt");

using (var reader = new StreamReader(stream, Encoding.UTF8, true, 4096, leaveOpen: true) {
    reader.ReadLine();
}

stream.Seek(0, SeekLocation.Begin);

using (var reader = new StreamReader(stream, Encoding.UTF8, true, 4096, leaveOpen: true) {
    // read the same line again
    reader.ReadLine();
}

跟踪流读取器线的位置

4 个答案: