"Program Files" folder

[John Emmas <johne53 tiscali co uk>]

I know that glib offers a function called g_get_home_dir() which returns the user's home folder on the 
relevant platform.  Is there any similar function that will give me the default folder for installing 
applications?  For example, on Windows this would return "C:\Program Files".  On Linux it might be "/bin" or 
"/usr/bin" or "/usr/local/bin" etc.  And on OS-X it would be "/Applications".

John