[futurebasic] Re: [FB] Permissions errors

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From: Robert Purves <robert.purves@...>
Date: Sun, 23 May 2004 22:41:41 +1200
  Robert Covington wrote:

> I tried to run Compositor from the CD
> ... when I quit, and it tried to write it's prefs on close, I got a  
> permissions error for File Ref 1

> DIM pBlock;128
> DIM pBlk&;128
> DIM @CreateFlag,@Drive%,@DirID&,@prefWDRef%
> Local Fn IsPrefsFolderThere
> Drive% = 0
> CreateFlag = _kDontCreateFolder
> FINDFOLDER(_kOnSystemDisk,_kPreferencesFolderType,CreateFlag,Drive%,Dir 
> ID&) = _NoErr
> pBlk& = @pBlock
> pBlk&.ioVRefNum% = Drive%
> pBlk&.ioWDDirID& = DirID&
> #if Carbonlib
> fn FBWDtoPBWD(@pBlk&)
> #endif
> IF FN OPENWD (pBlk&) = _noErr THEN prefWDRef% = pBlk&.ioVRefNum%
> END FN = prefWDRef%

I'm sure you are aware that the code above is rather, er, skanky.   
Despite its incomprehensibility / ugliness / obsolescence, it does try  
to signal an error by returning zero. If you ignore the signal and  

> OPEN "O", #1,_PrefFile$,,wdRef%

with wdRef% = 0, you end up attempting to write to a file in the same  
folder as the app. And if the latter is in a read-only location such as  
a CD, further errors naturally follow.

All routines that deal with files should detect errors, bail out on the  
first error, and return an error code to the calling routine. The  
caller, on seeing a code other than _noErr, should either present an  
alert to the user, or bail out and return the error code to *its*  

You may like to consider the merits of replacing your antiquated method  
with something based on GetUserPrefsFileSpec. This shows the  
recommended usage of FindFolder in OS X to locate the user's  
preferences folder.

'                           CPU : Carbon

local mode
local fn GetUserPrefsFileSpec( prefFileName as Str255, prefSpec as  
^FSSpec )
dim as long   @ dirID
dim as short  @ vRefNum
dim as OSErr    err

err = fn FindFolder( _kUserDomain, _kPreferencesFolderType,  
_kCreateFolder, @vRefNum, @dirID )
if ( err == _noErr ) then err = fn FSMakeFSSpec( vRefNum, dirID,  
prefFileName, #prefSpec )

end fn = err

dim as FSSpec  prefSpec
dim as OSErr   err

err = fn GetUserPrefsFileSpec( "Dumbo", @prefSpec )
select err
case _fnfErr
// the prefs file doesn't exist; you need to create it
case _noErr
// the prefs file already exists
case else
stop "GetUserPrefsFileSpec error " + str$( err )
end select

Robert P.