Directory Class: calculate the size of a directory

[C#]
// The following example calculates the size of a directory
// and its subdirectories, if any, and displays the total size
// in bytes.

using System;
using System.IO;

public class ShowDirSize
{
public static long DirSize(DirectoryInfo d)
{
long Size = 0;
// Add file sizes.
FileInfo[] fis = d.GetFiles();
foreach (FileInfo fi in fis)
{
Size += fi.Length;
}
// Add subdirectory sizes.
DirectoryInfo[] dis = d.GetDirectories();
foreach (DirectoryInfo di in dis)
{
Size += DirSize(di);
}
return(Size);
}
public static void Main(string[] args)
{
if (args.Length != 1)
{
Console.WriteLine("You must provide a directory argument at the command line.");
}
else
{
DirectoryInfo d = new DirectoryInfo(args[0]);
Console.WriteLine("The size of {0} and its subdirectories is {1} bytes.", d, DirSize(d));
}
}
}

[C++]