CODEWITHSUNDEEP
c#
RobertoNovelo
RobertoNovelo

Reputation: 3809

Add a line in a txt file

I have a txt file with data such as the following:

:10FF800000040B4E00040B4E00047D1400047D148D
:10FF900000040B4E0004CF6200040B4E00040B4E15
:10FFA00000040B4E00040B4E00040B4E00040B4EDD
:10FFB00000047D1400047D1400047D1400047D14ED
:10FFC00000040B4E000000000000000000000000D4
:10FFD0000000000000040B4E0000000000000000C4
:10FFE0000000000000000000000000000000000011
:10FFF0000000000000000000060000000000BFF844
:020000020000FC
:020000040014E6
:043FF0005AC8A58C7A
:00000001FF

what I want to do with my C# program is to add a line after or before a specific line, lets say add the line:

:020000098723060

before this line:

:020000020000FC

I have tried using the File.ReadLines("file.txt").Last(); but that just gives me the last one, what if i want the third or fourth? also, is there any way to identify the ":" in the file?

Upvotes: 1

Views: 2309

Answers (6)

Peter Wishart
Peter Wishart

Reputation: 12280

The ":" character doesn't really help the implementation, the lines are all newline-delimited already.

Here's an attempt at a method that doesn't load it all to memory or output to a different file.

Never cross the streams.

static Int32 GetCharPos(StreamReader s)
{
    var ia = BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.GetField;
    Int32 charpos = (Int32)s.GetType().InvokeMember("charPos", ia, null, s, null);
    Int32 charlen = (Int32)s.GetType().InvokeMember("charLen", ia, null, s, null);
    return (Int32)s.BaseStream.Position - charlen + charpos;
}

static void Appsert(string data, string precedingEntry = null)
{
    if (precedingEntry == null)
    {
        using (var filestream = new FileStream(dataPath, FileMode.Append))
        using (var tw = new StreamWriter(filestream))
        {
            tw.WriteLine(data);
            return;
        }
    }

    int seekPos = -1;
    using (var readstream = new FileStream(dataPath, 
        FileMode.Open, FileAccess.Read, FileShare.Write))
    using (var writestream = new FileStream(dataPath, 
        FileMode.Open, FileAccess.Write, FileShare.Read))
    using (var tr = new StreamReader(readstream))
    {
        while (seekPos == -1)
        {
            var line = tr.ReadLine();
            if (line == precedingEntry)
                seekPos = GetCharPos(tr);
            else if (tr.EndOfStream)
                seekPos = (int)readstream.Length;
        }

        writestream.Seek(seekPos, SeekOrigin.Begin);
        readstream.Seek(seekPos, SeekOrigin.Begin);
        int readLength = 0;
        var readBuffer = new byte[4096];
        var writeBuffer = new byte[4096];
        var writeData = tr.CurrentEncoding.GetBytes(data + Environment.NewLine);
        int writeLength = writeData.Length;
        writeData.CopyTo(writeBuffer, 0);
        while (true & writeLength > 0)
        {
            readLength = readstream.Read(readBuffer, 0, readBuffer.Length);
            writestream.Write(writeBuffer, 0, writeLength);
            var tmp = writeBuffer;
            writeBuffer = readBuffer;
            writeLength = readLength;
            readBuffer = tmp;
        }                
    }
}

Upvotes: 0

David Venegoni
David Venegoni

Reputation: 508

Here is a solution, though it may not be the best, it does work:

public void AddTextToFile(string filePath, int lineNumber, string txt) //zero based lineNumber
{
        Collection<string> newLines = new Collection<string>(File.ReadAllLines(filePath).ToList());


        if (lineNumber < newLines.Count)
            newLines.Insert(lineNumber, txt);
        else 
            newLines.Add(txt);

        using (StreamWriter writer = new StreamWriter(filePath, false))
        {
            foreach (string s in newLines)
                writer.WriteLine(s);
        }
}

And to answer your question about determining if ":" exists in a string, the answer is yes, in the example above, you could check if the line contains it by...

if(newLines[idx].Contains(':'))
//do something

Upvotes: 0

Sanjay Uttam
Sanjay Uttam

Reputation: 786

Not sure if you're trying to avoid reading the entire file in due to size, etc...but can't you just read the file and then replace...e.g.

var text = readFile(somePath);
writeFile( text.replace(":020000020000FC\n",":020000098723060\n:020000020000FC\n") , somePath);

Upvotes: 0

horgh
horgh

Reputation: 18533

I would say it is better to read and write line by line, especially if the target file tend to be of large size:

using (StreamReader r = new StreamReader("Test.txt"))
{
    using (StreamWriter w = new StreamWriter("TestOut.txt"))
    {
        while (!r.EndOfStream)
        {
            string line = r.ReadLine();
            w.WriteLine(line);
            if (line == ":020000020000FC")
                w.WriteLine(":020000098723060");
        }
        w.Close();
        r.Close();
    }
}

Upvotes: 2

Steve
Steve

Reputation: 216303

A brute force approach

string[] lines = File.ReadAllLines("file.txt");
using(StreamWrite sw = new StreamWriter("file.txt"))
{
   foreach(string line in lines)
   {
       if(line == ":020000020000FC")
          sw.WriteLine(":020000098723060");
       sw.WriteLine(line);
   }
}

Upvotes: 3

Jon Skeet
Jon Skeet

Reputation: 1500805

The simplest way - if you're happy to read the whole file into memory - would be just:

public void InsertLineBefore(string file, string lineToFind, string lineToInsert)
{
    List<string> lines = File.ReadLines(file).ToList();
    int index = lines.IndexOf(lineToFind);
    // TODO: Validation (if index is -1, we couldn't find it)
    lines.Insert(index, lineToInsert);
    File.WriteAllLines(file, lines);
}

public void InsertLineAfter(string file, string lineToFind, string lineToInsert)
{
    List<string> lines = File.ReadLines(file).ToList();
    int index = lines.IndexOf(lineToFind);
    // TODO: Validation (if index is -1, we couldn't find it)
    lines.Insert(index + 1, lineToInsert);
    File.WriteAllLines(file, lines);
}

There are significantly more efficient ways of doing this, but this approach is really simple.

Upvotes: 11

Related Questions