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Append text to file

Posted on 2016-07-14

1 solution

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Last Modified: 2016-07-18

I have a directory full of hundreds of text files. I need to loop through each of them, writing (appending) their contents to a single file.

This code is overwriting the target file with each new file the StreamReader opens. How do I append the text to the bottom of the target file instead of overwriting it?

static void Main(string[] args)
        {
            var sourceDirectory = @"C:\target\new\";
            var txtFiles = Directory.EnumerateFiles(sourceDirectory, "*.txt");

            foreach (string currentFile in txtFiles)
            {
                StreamReader exportedfiles = new StreamReader(currentFile, System.Text.Encoding.Default);

                using (FileStream readStream = File.OpenRead(currentFile))

                //Specify path for the combined file that will be created.
                using (FileStream writeStream = File.OpenWrite("C:\\file.txt"))
                {
                    BinaryReader reader = new BinaryReader(readStream);
                    BinaryWriter writer = new BinaryWriter(writeStream);

                    byte[] buffer = new byte[10240]; //Equals a 10mb buffer.
                    int bytesRead;

                    while ((bytesRead = readStream.Read(buffer, 0, 10240)) > 0)
                    {
                        writeStream.Write(buffer, 0, bytesRead);
                    }
                }
            }

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Question by:fcsIT

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4 Comments

LVL 34

Accepted Solution

by:it_saige

it_saige earned 2000 total points

ID: 417112512016-07-14

I would use File.ReadAllLines, File.WriteAllLines and File.AppendAllLines

Simple example based on your code -

using System.IO;

namespace EE_Q28957553
{
	class Program
	{
		static void Main(string[] args)
		{
			foreach (string path in Directory.EnumerateFiles(@"C:\target\new\", "*.txt"))
			{
				string[] lines = File.ReadAllLines(path);
				if (!File.Exists("C:\\file.txt"))
					File.WriteAllLines("C:\\file.txt", lines);
				else
					File.AppendAllLines("C:\\file.txt", lines);
			}
		}
	}
}

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-saige-

LVL 45

Expert Comment

by:AndyAinscow

ID: 417112532016-07-14

You run the following line for each file:
using (FileStream writeStream = File.OpenWrite("C:\\file.txt"))
which means you destroy it and recreate it for each file.

You need to re-organise the two loops (Not certain if I did the moving of lines - there might be a problem with closing braces but you get the idea)

static void Main(string[] args)
        {
            var sourceDirectory = @"C:\target\new\";
            var txtFiles = Directory.EnumerateFiles(sourceDirectory, "*.txt");

                //Specify path for the combined file that will be created.
                using (FileStream writeStream = File.OpenWrite("C:\\file.txt"))
                {
                    BinaryWriter writer = new BinaryWriter(writeStream);

            foreach (string currentFile in txtFiles)
            {
                StreamReader exportedfiles = new StreamReader(currentFile, System.Text.Encoding.Default);

                using (FileStream readStream = File.OpenRead(currentFile))
                    BinaryReader reader = new BinaryReader(readStream);


                    byte[] buffer = new byte[10240]; //Equals a 10mb buffer.
                    int bytesRead;

                    while ((bytesRead = readStream.Read(buffer, 0, 10240)) > 0)
                    {
                        writeStream.Write(buffer, 0, bytesRead);
                    }
                }
            }

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Author Comment

by:fcsIT

ID: 417112572016-07-14

You sir are a genius. That's so much easier than what I was trying to do, and it worked great, thank you so much!

LVL 30

Expert Comment

by:Olaf Doschke

ID: 417112792016-07-14

You don't even need a string array using ReadAllText()/AppendAllText(), but it's a good idea in terms of RAM usage and read/write flow to use a binary reader going through a smaller buffer. 10240 is 10KB, but already way better than reading byte by byte.

Bye, Olaf.

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