Text 1292, 95 rader
Skriven 2009-08-13 10:43:25 av mark lewis (1:3634/12.0)
   Kommentar till text 1291 av Sean Dennis (1:18/200)
Ärende: OS/2 programming question
=================================
ml> if tail (from the *nix tools) can read it while MAX is running, then 
ml> i'd say your problem is that you've not set your filemode to 
ml> shared-readonly before openingthe file... i'd have to go dig to find 
ml> the filemode needed but i suspect that is all it is...

 SD> Okay, if you can find it, let me know.  While I no longer am doing
 SD> the project I originally asked this question for, I can use it for
 SD> other projects. :) 


                               ----- Sharing Method -----
Access         Compatibility   Deny   Deny    Deny   Deny
Method            Mode         Both   Write   Read   None
---------------------------------------------------------
Read Only           0           16     32      48     64
Write Only          1           17     33      49     65
Read/Write          2*          18     34      50     66

 * = default


open a file RO and allow others full access, use filemode 64...
open a file RO and deny others read access, use filemode 48...
open a file RO and deny others write access, use filemode 32...
open a file RO and deny others all access, use filemode 16...

so, if reading a log being written by something else, even a separate thread in
your own app, i do something like this...

Const
  {FileMode constants}
  fmReadOnly  = $00;
  fmWriteOnly = $01;
  fmReadWrite = $02;
  fmDenyAll   = $10;  {prohibit both read and write access by others}
  fmDenyWrite = $20;  {prohibit write access by others}
  fmDenyRead  = $30;  {prohibit read access by others}
  fmDenyNone  = $40;  {allow full access by others}
  fmNoInherit = $80;  {file is private to current process and will
                       not be inherited by child processes}

Var
  oldmode : byte;
  theFile : file;
  thePath : string;
  

{code snip from center of spaghetti bowl}

oldmode := filemode;                  {save old filemode}
filemode := fmReadOnly + fmDenyNone;  {set new filemode}
assign(theFile,thePath);              {assign name to work var}
reset(theFile);                       {open existing file}
{do stuff with file here}
close(theFile);                       {close when finished}
filemode := oldmode;                  {restore filemode}

{end of code snip}


i always save the filemode and then restore it afterward... if you are opening
more tha one file at the same time, you need to ensure that each one is opened
in the necessary mode because filemode applies to all files opened after it is
set ... i have been known to have multiple filemode vars and even to go so far
as to have one for each file i open... i think my most "intricate" was where i
had multiple filemode vars for the files and a couple of files had more than
one filemode var... this was because i'd create a file or at least write to it
in one mode (fmWriteOnly+fmDenyAll) and then reopen it in another mode 
(fmReadWrite+fmDenyNone) or similar... it really depends on the needs of the
program, the file itself, and if you want to allow access to the file while you
are using it by others... i have seen many programs writing log files with
fmReadWrite+fmDenyAll so that they are the only program that can access the log
file while they are running... if MAX is in fmDenyAll or fmDenyRead mode, you
won't be able to access the log file at all while MAX is running... by the same
token, if you use the default fmReadWrite mode and MAX is in fmDenyWrite mode,
you won't be able to access the log file either...

filemode defaults to fmReadWrite... as shown above, just add them together...

eg:
filemode := fmReadOnly + fmDenyNone; # we read, anyone can read and write
filemode := fmReadOnly + fmDenyWrite; # we read, no one can write

fmNoInherit means file is private to current process and will not be inherited
by child processes...

these filemode values are standard... the above is simply an easy method of
using them... nothing special and should work in any programming language that
allows access to them...

HtH

)\/(ark

 * Origin:  (1:3634/12)