How do I test if a file stream is open?
in [Lisp]
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From: piscesboy on 31 Jan 2010 11:12 I have a recursive function that writes out to a file using (with-open- file). I pass a pointer to the file to be written as a parameter to recursive calls to the function. But if the file is already open I don't recursive calls to (with-open-file) to open it again. I need a way to test if the file pointer is already open and if it is, to simply use it to write to the file. Maybe there is a better way to do this altogether...?
From: sds on 31 Jan 2010 13:22 On Jan 31, 11:12 am, piscesboy <oraclmas...(a)gmail.com> wrote: > I have a recursive function that writes out to a file using (with-open- > file). I pass a pointer to the file to be written as a parameter to > recursive calls to the function. But if the file is already open I > don't recursive calls to (with-open-file) to open it again. I need a > way to test if the file pointer is already open and if it is, to > simply use it to write to the file. I am not sure what a "file pointer" is, but you might find OPEN-STREAM- P useful: http://www.lispworks.com/documentation/HyperSpec/Body/f_open_s.htm
From: piscesboy on 31 Jan 2010 13:34 On Jan 31, 1:22 pm, sds <sam.steing...(a)gmail.com> wrote: > On Jan 31, 11:12 am, piscesboy <oraclmas...(a)gmail.com> wrote: > > > I have a recursive function that writes out to a file using (with-open- > > file). I pass a pointer to the file to be written as a parameter to > > recursive calls to the function. But if the file is already open I > > don't recursive calls to (with-open-file) to open it again. I need a > > way to test if the file pointer is already open and if it is, to > > simply use it to write to the file. > > I am not sure what a "file pointer" is, but you might find OPEN-STREAM- > P useful:http://www.lispworks.com/documentation/HyperSpec/Body/f_open_s.htm I guess that's the C programmer in me talking. Thanks.
From: Paul Donnelly on 31 Jan 2010 16:41 piscesboy <oraclmaster(a)gmail.com> writes: > I have a recursive function that writes out to a file using (with-open- > file). I pass a pointer to the file to be written as a parameter to > recursive calls to the function. But if the file is already open I > don't recursive calls to (with-open-file) to open it again. I need a > way to test if the file pointer is already open and if it is, to > simply use it to write to the file. > > Maybe there is a better way to do this altogether...? Yeah, either drop the recursion and do your writing in a loop: (with-open-file (foo "file") (loop write to foo)) Or have two functions, one for the external interface and one for the loop: (defun write-out () (with-open-file (foo "file") (write-out1 foo))) (defun write-out1 (stream) write some stuff to stream (write-out1 stream)) If you've got initialization work to do, don't test whether you need to redo it every time through the loop. It may not be a bottleneck, especially since you're doing file IO, but come on.
From: Barry Margolin on 31 Jan 2010 20:16
In article <87aavux87t.fsf(a)plap.localdomain>, Paul Donnelly <paul-donnelly(a)sbcglobal.net> wrote: > piscesboy <oraclmaster(a)gmail.com> writes: > > > I have a recursive function that writes out to a file using (with-open- > > file). I pass a pointer to the file to be written as a parameter to > > recursive calls to the function. But if the file is already open I > > don't recursive calls to (with-open-file) to open it again. I need a > > way to test if the file pointer is already open and if it is, to > > simply use it to write to the file. > > > > Maybe there is a better way to do this altogether...? > > Yeah, either drop the recursion and do your writing in a loop: > > (with-open-file (foo "file") > (loop write to foo)) > > Or have two functions, one for the external interface and one for > the loop: > > (defun write-out () > (with-open-file (foo "file") > (write-out1 foo))) > > (defun write-out1 (stream) > write some stuff to stream > (write-out1 stream)) > > If you've got initialization work to do, don't test whether you need to > redo it every time through the loop. It may not be a bottleneck, > especially since you're doing file IO, but come on. You could do it all in one function: (defun write-out (... &optional stream) (flet ((write-out-internal (s) write stuff to s ;; and recurse (write-out ... stream))) (if stream (write-out-internal s) (with-open-file (new-stream...) (write-out-internal ... new-stream))))) -- Barry Margolin, barmar(a)alum.mit.edu Arlington, MA *** PLEASE post questions in newsgroups, not directly to me *** *** PLEASE don't copy me on replies, I'll read them in the group *** |