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C# Cookbook by Jay Hilyard, Stephen Teilhet

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11.20. Write to Multiple Output Files at One Time

Problem

Any output that is written to one file must also be written to at least one other file. Essentially, you want to end up with at least the original file and the duplicate file.

Solution

Create a class called MultiWriter with the ability to write to multiple files from a single WriteLine call.

To create a set of files, just pass the file paths you would like to use to the constructor like this:

// Create a list of three file names
string[] names = new string[3];
for (int i=0;i<3;i++)
{
    names[i] = Path.GetTempFileName( );
}
MultiWriter multi = new MultiWriter(names);

Next, perform the writes and close the instance:

multi.WriteLine("First Line");
multi.WriteLine("Second Line");
multi.WriteLine("Third Line");
multi.Close( );

Here is the implementation of the MultiWriter class:

class MultiWriter : IDisposable { FileStream[] _streams; string [] _names; int _streamCount = 0; bool _disposed = false; public MultiStream(string[] fileNames) { try { // copy the names _names = (string[])fileNames.Clone( ); // set the number of streams _streamCount = fileNames.Length; // make the stream array _streams = new FileStream[_streamCount]; for(int i = 0; i < _streams.Length; i++) { // create this filestream _streams[i] = new FileStream(_names[i], FileMode.Create, FileAccess.ReadWrite, FileShare.None); } } catch(IOException ioe) { Console.WriteLine(ioe.ToString( )); } } public void WriteLine(string text) { // add a newline text += Environment.NewLine; ...

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