Reading an unsigned 24-bit integer from a C# stream

Question

What is the best way to read an unsigned 24-bit integer from a C# stream using BinaryReader?

So far I used something like this:

private long ReadUInt24(this BinaryReader reader)
{
    try
    {
        return Math.Abs((reader.ReadByte() & 0xFF) * 256 * 256 + (reader.ReadByte() & 0xFF) * 256 + (reader.ReadByte() & 0xFF));
    }
    catch
    {
        return 0;
    }
}

Is there any better way to do this?

Answer 1

Some quibbles with your code

• You question and signature say unsigned but you return a signed value from the function
• Byte in .Net is unsigned but you're using signed values for arithmetic forcing a later use of Math.Abs. Use all unsigned calculations to avoid this.
• IMHO it's cleaner to shift bits using shift operators instead of multiplication.
• Silently catching the exception is likely the wrong idea here.

I think it's more readable to do the following

private static uint ReadUInt24(this BinaryReader reader) {
    try {
        var b1 = reader.ReadByte();
        var b2 = reader.ReadByte();
        var b3 = reader.ReadByte();
        return 
            (((uint)b1) << 16) |
            (((uint)b2) << 8) |
            ((uint)b3);
    }
    catch {
        return 0u;
    }
}

Answer 2

This looks pretty elegant to me.

private static long ReadUInt24(this BinaryReader reader)
{
  try
  {
    byte[] buffer = new byte[4];
    reader.Read(buffer, 0, 3);
    return (long)BitConverter.ToUInt32(buffer, 0);
  }
  catch 
  { 
    // Swallowing the exception here might not be a good idea, but that is a different topic.
    return 0;
  }
}