Question

How do I use the Stream CopyTo method without overwriting the existing output file?

public void MergeAndDeleteFiles(string outputFile, IEnumerable<string> inputFiles)
        {
            using (var output = File.OpenWrite(outputFile))
            {
                foreach (var inputFile in inputFiles)
                {
                    using (var input = File.OpenRead(inputFile))
                    {
                        input.CopyTo(output);
                    }
                }
             }
        }

The above method overwrites the outputFile for some reason? DO i need to set the position of the output file before using the CopyTo method?

Answer 1

Instead of OpenWrite use Open and pass in FileMode.Append:

using (var output = File.Open(outputFile, FileMode.Append))

This will append the output to the end of the file.