a665@mindlink.UUCP (Anthon Pang) (12/05/90)
First of all, IMO, CurrentDir takes the old lock, frees it, and gives you a new one. Secondly, NULL isn't a valid lock value (returned by Lock, CurrentDir, DupLock...)...it is used as a function parameter to specify the root directory or system volume. -- Disclaimer: just pulled an all nighter...so all of this is just MHO and swiss-cheese memory.
laughlin@fornax.UUCP (Bob Laughlin) (12/05/90)
I've been using the following code to move around directories
from within a program and restore the original current directory
on termination. It seems to work and I originally got the code
from an example posted here a few years ago.
// at program startup store a lock on the current directory
if ((startdir = Lock ("", ACCESS_READ)) == NULL)
error ...
........
// during the program move around the directories with ...
if ((newlock = Lock (newdir, ACCESS_READ) != NULL) {
oldlock = CurrentDir (newlock) ; // oldlock == NULL is a valid lock!
UnLock (oldlock) ;
}
........
// at program termination restore the original directory
oldlock = CurrentDir (startdir) ;
UnLock (oldlock) ;
However, reading Rob Peck's Programmer's Guide to the Amiga
lately I notice that on page 30 it states that you should NOT
call UnLock() on locks obtained from a call to CurrentDir().
Also, the 1.3 AutoDocs only mention using UnLock() on a lock obtained
from Lock(), DupLock(), or CreateDir(). If this is correct then how do
you move around directories without leaving any locks around when the
program exits?
My guess is that you something like the following:
// at program startup store a lock on the current directory
startdir = Lock ("", ACCESS_READ) ;
........
// during the program move around the directories with ...
if ((newlock = Lock (newdir, ACCESS_READ) != NULL)
CurrentDir (newlock) ;
...... use newlock
UnLock (newlock) ;
}
........
// at program termination restore the original directory
CurrentDir (startdir) ;
UnLock (startdir) ;
Is this correct?
--
Bob Laughlin laughlin@cs.sfu.ca ken@cbmvax.commodore.com (Ken Farinsky - CATS) (12/06/90)
In article <4046@mindlink.UUCP> a665@mindlink.UUCP (Anthon Pang) writes: >First of all, IMO, CurrentDir takes the old lock, frees it, and gives you a new >one. Secondly, NULL isn't a valid lock value (returned by Lock, CurrentDir, >DupLock...)...it is used as a function parameter to specify the root directory >or system volume. CurrentDir does not free anything. NULL is a valid result. When in doubt, consult the documentation: dos.library/CurrentDir dos.library/CurrentDir NAME CurrentDir -- Make a directory associated with a lock the working directory SYNOPSIS oldLock = CurrentDir( lock ) D0 D1 struct FileLock *oldlock, *lock; FUNCTION CurrentDir() causes a directory associated with a lock to be made the current directory. The old current directory lock is returned. A value of zero is a valid result here, this 0 lock represents the root of fiat you booted from (which is, in effect, the parent of all other file system roots.) INPUTS lock - BCPL pointer to a lock OUTPUTS oldLock - BCPL pointer to a lock SEE ALSO Lock -- -- Ken Farinsky - CATS - (215) 431-9421 - Commodore Business Machines uucp: ken@cbmvax.commodore.com or ...{uunet,rutgers}!cbmvax!ken bix: kfarinsky