Removing the first line of a text file in C#
Instead of lines.Take
, you can use lines.Skip
, like:
var lines = File.ReadAllLines("test.txt");
File.WriteAllLines("test.txt", lines.Skip(1).ToArray());
to truncate at the beginning despite the fact that the technique used (read all text and write everything back) is very inefficient.
About the efficient way: The inefficiency comes from the necessity to read the whole file into memory. The other way around could easily be to seek in a stream and copy the stream to another output file, delete the original, and rename the old. That one would be equally fast and yet consume much less memory.
Truncating a file at the end is much easier. You can just find the trunaction position and call FileStream.SetLength()
.
Here is an alternative:
using (var stream = File.OpenRead("C:\\yourfile"))
{
var items = new LinkedList<string>();
using (var reader = new StreamReader(stream))
{
reader.ReadLine(); // skip one line
string line;
while ((line = reader.ReadLine()) != null)
{
//it's far better to do the actual processing here
items.AddLast(line);
}
}
}
Update
If you need an IEnumerable<string>
and don't want to waste memory you could do something like this:
public static IEnumerable<string> GetFileLines(string filename)
{
using (var stream = File.OpenRead(filename))
{
using (var reader = new StreamReader(stream))
{
reader.ReadLine(); // skip one line
string line;
while ((line = reader.ReadLine()) != null)
{
yield return line;
}
}
}
}
static void Main(string[] args)
{
foreach (var line in GetFileLines("C:\\yourfile.txt"))
{
// do something with the line here.
}
}
var lines = System.IO.File.ReadAllLines("test.txt");
System.IO.File.WriteAllLines("test.txt", lines.Skip(1).ToArray());
Skip
eliminates the given number of elements from the beginning of the sequence. Take
eliminates all but the given number of elements from the end of the sequence.