How to read multiple text files and save them into one text file?

Question

Hello,

In my case I have five huge text files,which I have to embedd into one text file.

I tried with StreamReader(),but I don't know how to make it Read one more file,do I have to assign another variable?

Showing an example will be appreciated greatfully.

Answer 1

New answer

(See explanation for junking original answer below.)

static void CopyFiles(string dest, params string[] sources)
{
    using (TextWriter writer = File.CreateText(dest))
    {
        // Somewhat arbitrary limit, but it won't go on the large object heap
        char[] buffer = new char[16 * 1024]; 
        foreach (string source in sources)
        {
            using (TextReader reader = File.OpenText(source))
            {
                int charsRead;
                while ((charsRead = reader.Read(buffer, 0, buffer.Length)) > 0)
                {
                    writer.Write(buffer, 0, charsRead);
                }
            }
        }
    }
}

This new answer is quite like Martin's approach, except:

• It reads into a smaller buffer; 16K is going to be acceptable in almost all situations, and won't end up on the large object heap (which doesn't get compacted)
• It reads text data instead of binary data, for two reasons:
  • The code can easily be modified to convert from one encoding to another
  • If each input file contains a byte-order mark, that will be skipped by the reader, instead of ending up with byte-order marks scattered through the output file at input file boundaries

Original answer

Martin Stettner pointed out an issue in the answer below - if the first file ends without a newline, it will still create a newline in the output file. Also, it will translate newlines into the "\r\n" even if they were previously just "\r" or "\n". Finally, it pointlessly risks using large amounts of data for long lines.

Something like:

static void CopyFiles(string dest, params string[] sources)
{
    using (TextWriter writer = File.CreateText(dest))
    {
        foreach (string source in sources)
        {
            using (TextReader reader = File.OpenText(source))
            {
                string line;
                while ((line = reader.ReadLine()) != null)
                {
                    writer.WriteLine(line);
                }
            }
        }
    }
}

Note that this reads line by line to avoid reading too much into memory at a time. You could make it simpler if you're happy to read each file completely into memory (still one at a time):

static void CopyFiles(string dest, params string[] sources)
{
    using (TextWriter writer = File.CreateText(dest))
    {
        foreach (string source in sources)
        {
            string text = File.ReadAllText(source);
            writer.Write(text);
        }
    }
}

Answer 2

Edit:

As Jon Skeet pointed out, text files usually should be handled differently than binary files .

I just leave this answer since it might be more performant if you have really big files and aren't concernded by encoding issues (such as different input files having different encodings or multiple Byte Order Marks in the output file):

public void CopyFiles(string destPath, string[] sourcePaths) {
  byte[] buffer = new byte[10 * 1024 * 1024]; // Just allocate a buffer as big as you can afford
  using (var destStream= = new FileStream(destPath, FileMode.Create) {
    foreach (var sourcePath in sourcePaths) {
      int read;
      using (var sourceStream = FileStream.Create(sourcePath, FileMode.Open) {
        while ((read = sourceStream.Read(buffer, 0, 10*1024*1024)) != 0)
          destStream.Write(buffer, 0, read);
      }
    }
  }
}