Read from a file starting at the end, similar to tail
In native C#开发者_StackOverflow中文版, how can I read from the end of a file?
This is pertinent because I need to read a log file, and it doesn't make sense to read 10k, to read the last 3 lines.
To read the last 1024 bytes:
using (var reader = new StreamReader("foo.txt"))
{
if (reader.BaseStream.Length > 1024)
{
reader.BaseStream.Seek(-1024, SeekOrigin.End);
}
string line;
while ((line = reader.ReadLine()) != null)
{
Console.WriteLine(line);
}
}
Maybe something like this will work for you:
using (var fs = File.OpenRead(filePath))
{
fs.Seek(0, SeekOrigin.End);
int newLines = 0;
while (newLines < 3)
{
fs.Seek(-1, SeekOrigin.Current);
newLines += fs.ReadByte() == 13 ? 1 : 0; // look for \r
fs.Seek(-1, SeekOrigin.Current);
}
byte[] data = new byte[fs.Length - fs.Position];
fs.Read(data, 0, data.Length);
}
Take note that this assumes \r\n
.
The code below uses a random-access FileStream
to seed a StreamReader
at an offset near the end of the file, discarding the first read line since it is most likely only partial.
FileStream stream = new FileStream(@"c:\temp\build.txt",
FileMode.Open, FileAccess.Read);
stream.Seek(-1024, SeekOrigin.End); // rewind enough for > 1 line
StreamReader reader = new StreamReader(stream);
reader.ReadLine(); // discard partial line
while (!reader.EndOfStream)
{
string nextLine = reader.ReadLine();
Console.WriteLine(nextLine);
}
Take a look at this related question's answer to read a text file in reverse. There is a lot of complexity to reading a file backward correctly because of stuff like encoding.
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