Trim a text file to desired length [closed]

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How would I write a function that trims a text file approximately to desired size in bytes? The file is a newline-separated list and I w开发者_JAVA百科ould like to trim it between the elements, not inside them.

EDIT: Example file

element one
element two
third element
hello
final element

I'd like to to cut off the file in a way that elements are kept intact, e.g. not like this:

element one
element two
third element
he

But like this (even if it means that the size won't be exactly equal to the parameter):

element one
element two
third element

---

This will read the desired length and then trim it to the last newline:

 protected static string GetString(string filename, int contentLength)
    {
        string retString;
        using (FileStream fs = new FileStream(filename, FileMode.Open))
        {
            int length = (fs.Length < contentLength ? (int)fs.Length : contentLength);
            byte[] b = new byte[length];
            fs.Read(b, 0, contentLength);
            string str = System.Text.ASCIIEncoding.UTF8.GetString(b);
            if (str.LastIndexOf("\r") > 0)
                retString = str.Substring(0, str.LastIndexOf("\r"));
            else
                retString = str;
        }
        return retString;
    }

Then call it like this to write to new file:

string filename = "c:\\test.txt";
File.WriteAllText(filename,GetString(filename, 100));

---

    public static void TrimTextFile(string fileName, long sizeInByte)
    {
        using(FileStream fs = new FileStream(fileName, FileMode.Open))
        {
            fs.Position = sizeInByte;
            int byteRead = 0;
            while ((byteRead = fs.ReadByte()) >= 0)
            {
                if(byteRead == 13)
                {
                    fs.SetLength(fs.Position - 1);
                    break;

                }
            }
        }
    }

---

This sample code will continue reading lines writing them away again to another file up to a maximum file size specified. It converts each read line to your desired character encoding to determine its length in bytes.

Code is written without compile check.

var input = new FileStream(inputFilename, FileMode.Open);
var output = new FileStream(outputFilename, FileMode.Create);
var reader = new StreamReader(input);
var writer = new BinaryWriter(output);
var data = reader.ReadLine();
var maxSize = 10000;
var totalLength = 0;
while (!string.IsNullOrWhitespace(data) && totalLength < maxSize)
{
  var bytes = System.Text.UnicodeEncoding.GetBytes(data);
  totalLength += bytes.GetLength(0);
  if totalLength < maxSize) writer.Write(bytes);
  data = reader.ReadLine();
}
writer.Flush();
writer.Close();
reader.Close();