C# Signature:

[DllImport("kernel32.dll", SetLastError=true, CharSet=CharSet.Auto)]
static extern bool GetDiskFreeSpaceEx(string lpDirectoryName,
   out ulong lpFreeBytesAvailable,
   out ulong lpTotalNumberOfBytes,
   out ulong lpTotalNumberOfFreeBytes);

User-Defined Types:

None.

Notes:

None.

Tips & Tricks:

None.

Sample Code:

ulong FreeBytesAvailable;
ulong TotalNumberOfBytes;
ulong TotalNumberOfFreeBytes;

GetDiskFreeSpaceEx("C:\\", out FreeBytesAvailable, out TotalNumberOfBytes,
          out TotalNumberOfFreeBytes);

Console.WriteLine("Free Bytes Available:      {0,15:D}", FreeBytesAvailable);
Console.WriteLine("Total Number Of Bytes:     {0,15:D}", TotalNumberOfBytes);
Console.WriteLine("Total Number Of FreeBytes: {0,15:D}", TotalNumberOfFreeBytes);

Alternative Managed API:

Starting in v2.0 (Whidbey) of the .NET Framework, this is exposed through the System.Io.DriveInfo class.