Recipe12.20.Writing to Multiple Output Files at One Time

Recipe 12.20. Writing 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 a 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 filenames. 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( );

Example 12-10 is the implementation of the MultiWriter class.

Example 12-10. MultiWriter class

 class MultiWriter : IDisposable {     FileStream[] _streams;     string [] _names;     int _streamCount = 0;     bool _disposed = false;     public MultiWriter(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 file stream.                 _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;         // Get the bytes in unicode format…         byte[] bytes = Encoding.ASCII.GetBytes(text);         // Roll over the streams.         for(int i = 0; i < _streams.Length; i++)         {             // Write the text.             _streams[i].Write(bytes,0,bytes.Length);         }     }     public void Close( )     {         Dispose( );     }     public void Dispose( )     {         Dispose(true);         // Prevent refinalizing.         GC.SuppressFinalize(this);     }     protected void Dispose(bool disposing)     {         try         {             // Only close out once.             if(_disposed == false && disposing == true)             {                 // Close each stream.                 for(int i=0;i<_streams.Length;i++)                 {                     _streams[i].Close( );                 }                 // Indicate we have done this already.                 _disposed = true;             }         }         catch(IOException ioe)         {             Console.WriteLine(ioe);         }     }     ~MultiWriter()     {         Dispose(false);     } }

Discussion

MultiWriter implements the IDisposable interface, which helps the users remember to close the files this will create. Ultimately, if the user forgets to call Close (a thin wrapper around Dispose for semantic convenience), the finalizer (~MultiWriter) will call Dispose anyway and close the files when the garbage collector finalizes the instance. Note that in the public Dispose method, we call the protected Dispose method, which closes the file streams we created internally and calls the GC. SuppressFinalize method. This is an optimization to keep the garbage collector from having to call our finalizer.