excel - What do the hash signs in #if, #else, #end if mean?

Question

I'm writing code to check if a file is available to be checked out of SharePoint and, if it isn't, alert the user and tell them that the file is in use by someone else and who has it in use.

I came across a piece of code at http://www.xcelfiles.com/IsFileOpen.html#anchor_37

The code seems to work in test scenarios so I am planning to adapt it for my purposes. I'm having trouble understanding some of the syntax.

#If Not VBA6 Then

'// Xl97

For i = j - 1 To 1 Step -1

    If Mid(strXl, i, 1) = Chr(0) Then Exit For

Next

i = i + 1

#Else

'// Xl2000+

i = InStrRev(strXl, strFlag1, j) + Len(strFlag1)

#End If

I understand what the code does but I don't get the significance of the '#' symbol.

Another example:

hdlFile = FreeFile

Open strPath For Binary As #hdlFile

strXl = Space(LOF(hdlFile))

Get 1, , strXl

Close #hdlFile

It is a pain to google because it is so vague.

Answer 1

The hash symbols represent a preprocessor command, which are commands that are processed prior to compilation, essentially producing dynamic / conditional code. These types of commands are often used in languages such as C/C++ to manage cross-platform programming techniques. A common usage is to check for a particular environment or platform (ie. VBA, Windows, MacOSX, etc), and then implement platform-specific code.

http://en.wikipedia.org/wiki/Preprocessor