使用StreamReader读取特定行

Question

I have a problem with the stream reader. i want to read from a text file just one line.

I want a specific line, like the seventh line. and i don't know how to.

it's a function or something like that ? like file.ReadLine(number 7) ?

Answer 1

The simplest approach would probably be to use LINQ combined with File.ReadLines :

string line = File.ReadLines("foo.txt").ElementAt(6); // 0-based

You could use File.ReadAllLines instead, but that would read the whole file even if you only want an early one. If you need various different lines of course, it means you can read them in one go. You could write a method to read multiple specific lines efficiently (ie in one pass, but no more than one line at a time) reasonably easily, but it would be overkill if you only want one line.

Note that this will throw an exception if there aren't enough lines - you could use ElementAtOrDefault if you want to handle that without any exceptions.

Answer 2

If you want to read line by number it's better to use

string line = File.ReadLines(fileName).Skip(N).FirstOrDefault();

Thus you will avoid reading all lines from file, and you'll read lines only until you get line you need. If you need several lines, then it's better to read all lines to array, and then get your lines from that array:

 string[] lines = File.ReadAllLines(fileName);

 if (lines.Count() > N)
     line = lines[N];

Answer 3

if you want to specific line by using StreamReader. Suppose you have a data Line1,Line2,Line3,Line4 in text files. Every time you call "ReadLine" method it will increase 1 line. That mean you can write you own function and passing your parmeter to function. You can do it by.

string l1, l2, l3, l4;
StreamReader sr = new StreamReader(sourcePath);
l1 = sr.Readline(); // Line 1
l2 = sr.Readline(); // Line 2
l3 = sr.Readline(); // Line 3


  public string StreamReadLine(string sourcepath, int lineNum)
    {
      int index = lineNum;
      string strLine = "N/A";
      StreamReader sr = new StreamReader(sourcepath);
     try
    {
       for (var i = 0; i <= index; i++)
       {
         strLine = sr.ReadLine();
         if (i == index)
             break;
         i += 1;
       }
   }
   catch (Exception ex)
   {
     strLine = ex.ToString();
   }
return strLine;

}