Writing to free space

Question

I was wondering if It is possible to write to freespace in C#? I mean something like FreeSpace.WriteAllBytes() or like what some shredder apps do?

How can I do so?

Answer 1

If your intention is simply to overwrite all the free space available on a hard drive, you can use the GetDiskFreeSpaceEx API to determine how many bytes are available and write a file that large (or spread it out among several files).

P/Invoke for C#:

[DllImport("kernel32")]
public static extern int GetDiskFreeSpaceExW(string dir, ref ulong freeBytesAvailable,
    ref ulong totalNumBytes, ref ulong totalFreeBytes);

You can use a class like System.Random to fill an array of bytes with random values before writing them, if that might interest you.

Edit: Wasn't aware of the System.IO.DriveInfo class, which could be simpler than using the mentioned API.

Answer 2

Such specific functionality is not built into C#, but you could easily write it yourself, by opening a file and writing bytes (0) into it until the disk is full.

Take note some file systems will limit your max file size.

Answer 3

This has worked for me to get the free space of a drive (C#), via System.Management

ManagementObject di = new ManagementObject("win32_logicaldisk.deviceid=\"C:\"");
di.Get();
UInt64 freeSpace = (UInt64)di["FreeSpace"]; //in bytes

Now you can write files named via System.Guid.NewGuid() to fill up all the space (use a multiple of the filesystem's cluster size).