C# How to skip number of lines while reading text

问题:

I have a program which reads a text file and processes it to be seperated into sections.

So the question is how can the program be changed to allow the program to skip reading the first 5 lines of the file while using the Stream Reader to read the file?

Could someones please advise on the codes? Thanks!

The Codes:

class Program
{
    static void Main(string[] args)
    {
        TextReader tr = new StreamReader(@"C:\Test\new.txt");

        String SplitBy = "----------------------------------------";

        // Skip first 5 lines of the text file?
        String fullLog = tr.ReadToEnd();

        String[] sections = fullLog.Split(new string[] { SplitBy }, StringSplitOptions.None);

        //String[] lines = sections.Skip(5).ToArray();

        foreach (String r in sections)
        {
            Console.WriteLine(r);
            Console.WriteLine("============================================================");
        }
    }
}

回答1:

Try the following

// Skip 5 lines
for(var i = 0; i < 5; i++) {
  tr.ReadLine();
}

// Read the rest
string remainingText = tr.ReadToEnd();

回答2:

If the lines are fixed then the most efficient way is as follows:

using( Stream stream = File.Open(fileName, FileMode.Open) )
{
    stream.Seek(bytesPerLine * (myLine - 1), SeekOrigin.Begin);
    using( StreamReader reader = new StreamReader(stream) )
    {
        string line = reader.ReadLine();
    }
}

And if the lines vary in length then you'll have to just read them in a line at a time as follows:

using (var sr = new StreamReader("file"))
{
    for (int i = 1; i <= 5; ++i)
        sr.ReadLine();
}

回答3:

If you want to use it more times in your program then it maybe a good idea to make a custom class inherited from StreamReader with the ability to skip lines.

Something like this could do:

class SkippableStreamReader : StreamReader
{
    public SkippableStreamReader(string path) : base(path) { }

    public void SkipLines(int linecount)
    {
        for (int i = 0; i < linecount; i++)
        {
            this.ReadLine();
        }
    }
}

after this you could use the SkippableStreamReader's function to skip lines. Example:

SkippableStreamReader exampleReader = new SkippableStreamReader("file_to_read");

//do stuff
//and when needed
exampleReader.SkipLines(number_of_lines_to_skip);

回答4:

I'll add two more suggestions to the list.

If there will always be a file, and you will only be reading, I suggest this:

var lines = File.ReadLines(@"C:\Test\new.txt").Skip(5).ToArray();

File.ReadLines doesn't block the file from others and only loads into memory necessary lines.

If your stream can come from other sources then I suggest this approach:

class Program
{
    static void Main(string[] args)
    {
        //it's up to you to get your stream
        var stream = GetStream();

        //Here is where you'll read your lines. 
        //Any Linq statement can be used here.
        var lines = ReadLines(stream).Skip(5).ToArray();

        //Go on and do whatever you want to do with your lines...
    }
}

public IEnumerable<string> ReadLines(Stream stream)
{
    using (var reader = new StreamReader(stream))
    {
        while (!reader.EndOfStream)
        {
            yield return reader.ReadLine();
        }
    }
}

The Iterator block will automatically clean itself up once you are done with it. Here is an article by Jon Skeet going in depth into how that works exactly (scroll down to the "And finally..." section).

回答5:

I'd guess it's as simple as:

    static void Main(string[] args)
    {
        var tr = new StreamReader(@"C:\new.txt");

        var SplitBy = "----------------------------------------";

        // Skip first 5 lines of the text file?
        foreach (var i in Enumerable.Range(1, 5)) tr.ReadLine();
        var fullLog = tr.ReadToEnd(); 

        String[] sections = fullLog.Split(new string[] { SplitBy }, StringSplitOptions.None);

        //String[] lines = sections.Skip(5).ToArray();

        foreach (String r in sections)
        {
            Console.WriteLine(r);
            Console.WriteLine("============================================================");
        }
    }