组合多个文本文件的有效方法

Question

I have multiple files of text that I need to read and combine into one file. The files are of varying size: 1 - 50 MB each. What's the most efficient way to combine these files without bumping into the dreading System.OutofMemoryException ?

Answer 1

Do it in chunks:

const int chunkSize = 2 * 1024; // 2KB
var inputFiles = new[] { "file1.dat", "file2.dat", "file3.dat" };
using (var output = File.Create("output.dat"))
{
    foreach (var file in inputFiles)
    {
        using (var input = File.OpenRead(file))
        {
            var buffer = new byte[chunkSize];
            int bytesRead;
            while ((bytesRead = input.Read(buffer, 0, buffer.Length)) > 0)
            {
                output.Write(buffer, 0, bytesRead);
            }
        }
    }
}

Answer 2

Darin is on the right track. My tweak would be:

using (var output = File.Create("output"))
{
    foreach (var file in new[] { "file1", "file2" })
    {
        using (var input = File.OpenRead(file))
        {
            input.CopyTo(output);
        }
    }
}

Answer 3

This is code used above for.Net 4.0, but compatible with.Net 2.0 (for text files)

using (var output = new StreamWriter("D:\\TMP\\output"))
{
  foreach (var file in Directory.GetFiles("D:\\TMP", "*.*"))
  {
    using (var input = new StreamReader(file))
    {
      output.WriteLine(input.ReadToEnd());
    }
  }
}

Please note that this will read the entire file in memory at once. This means that large files will cause a lot of memory to be used (and if not enough memory is available, it may fail all together).