Binary Writer/Reader extra character

Question

I am converting some legacy VB6 code to C# and this just has me a little baffled. The VB6 code wrote certain data sequentially to a file. This data is always 110 bytes. I can read this file just fine in the converted code, but I'm having trouble with when I write the file from the converted code.

Here is a stripped down sample I wrote real quick in LINQPad:

void Main()
{
  int[,] data = new[,]
  {
    {
      0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19
    },
    {
      20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39
    }
  };

  using ( MemoryStream stream = new MemoryStream() )
  {
    using ( BinaryWriter writer = new BinaryWriter( stream, Encoding.ASCII, true ) )
    {
      for( var i = 0; i < 2; i++ )
      {
        byte[] name = Encoding.ASCII.GetBytes( "Blah" + i.ToString().PadRight( 30, ' ' ) );

        writer.Write( name );
        for( var x = 0; x < 20; x++ )
        {
          writer.Write( data[i,x] );
        }
      }
    }

    using ( BinaryReader reader = new BinaryReader( stream ) )
    {
      // Note the extra +4 is because of the problem below.
      reader.BaseStream.Seek( 30 + ( 20 * 4 ) + 4, SeekOrigin.Begin );

      string name = new string( reader.ReadChars(30) );
      Console.WriteLine( name );

      // This is the problem..This extra 4 bytes should not be here.
      //reader.ReadInt32();

      for( var x = 0; x < 20; x++ )
      {
        Console.WriteLine( reader.ReadInt32() );
      }
    }
  }
}

As you can see, I have a 30 character string written first. The string is NEVER longer than 30 characters and is padded with spaces if it is shorter. After that, twenty 32-bit integers are written. It is always 20 integers. So I know each character in a string is one byte. I know a 32 bit integer is four bytes. So in my reader sample, I should be able to seek 110 bytes ( 30 + (4 * 20) ), read 30 chars, and then read 20 ints and that's my data. However, for some reason, there is an extra 4 bytes being written after the string.

Am I just missing something completely obvious (as is normally the case for myself)? Strings aren't null terminated in .Net and this is four bytes anyway, not just an extra byte? So where is this extra 4 bytes coming from? I'm not directly calling Write(string) so it can't be a prefixed length, which it's obviously not since it's after my string. If you uncomment the ReadInt32(), it produces the desired result.

Answer 1

The extra 4 bytes are from the extra 4 characters you're writing. Change the string you're encoding as ASCII to this:

("Blah" + i.ToString()).PadRight(30, ' ')

That is, pad the string after you've concatenated the prefix and the integer.