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LogDev.pas (c) Copyright M.P.B. Cole, 1990,1991,1995.
All Rights Reserved.
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This unit implements a Turbo Pascal "Text Device" which formats
output in a form suitable for Opus\Binkley, FrontDoor or D'Bridge
style LOG files. If you find it of use and want to say so (you'd
be the first but still...) I can be reached via Fidonet mail at
2:441/286 or PascalNet 115:4401/1 (Limited hours, no Crash Mail).
VERSION 1.7
Turbo/Borland Pascal versions 4 to 7
You are free to use and adapt this code with the following
restrictions.
1) You MAY NOT use this code in any commercial application or in
a "Shareware" or any other such application which requests
payment from the user, without express permission from the
copyright holder. Such permission is unlikely to be withheld
but I shall probably expect a freebi in return!
2) You are free to distribute the original version of this code
as long as you do not demand payment other than a nominal one
to cover your costs (such as a BBS registration fee or
postage) and in any event such a charge is not to exceed 5UKP
unless it is a BBS Registration fee. Please distribute the
source code (logdev.pas), the documentation (Logdev.doc) and
the example program (logtest.pas) together and ensure that the
distribution file name clearly indicates the version number.
Preferably as an archive file named LOGPASxx.??? (eg.
LOGPAS14.ARJ).
3) You MAY NOT distribute altered versions of this code unless
you distribute them with an altered file name AND with my
original code included AND with all changes documented (in a
seperate document). The distributed code MUST retain my
copyright message and must bear the same restrictions on use
as the original.
4) Naturally I would be delighted to here from anyone who finds
this code useful (never have in the past though) and would not
object at all to being given due credit in any program of
yours that uses it.
This code is not warranted to do anything except waste space on
your system. If it works, great, if it does not I accept no
responsibliliy for any damage it may do. If you cannot accept
that condition then please do not use LOGDEV.
Of course it works for me, but that may be luck!
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*Warning: I wrote the initial LogDev in 1989 planning to release
it in the near future. Since then it has undergone extensive
changes. The original documention was written soon after the
first version of the code and has not always (well alright,
almost never) been corrected for changes. Until now that is. So
with the best will in the world (?) it is likely that there are
still mistakes in it. For these I apologise. Actually the unit
is quite easy to use so rotten documentation should do little
harm (who reads it anyway!).
In fact you could consider it a bonus with free software. With
commercial software you have to PAY to get rotten documentation.
This document is broken into the following sections:
Overview
LogDev Usage
LogDev in use
Important Notes
Adding your own log format
No index, find 'em yourself!
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Overview
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This unit implements a Turbo Pascal "Text File Device" which
formats output in a form suitable for Opus\Binkley, FrontDoor or
D'Bridge style LOG files. Assigning a file to this driver makes
it simple for a program to update its log and give users a choice
of log formats.
To use the unit you use the procedure "AssignLog" to assign a
TEXT file to the device, open the file with the normal Turbo
REWRITE or APPEND procedures and then WRITE or WRITELN entries to
the log just as you would to any TEXT file. LogDev takes care of
forrmatting the entry correctly for your chosen log type and adds
the appropriate date and time stamp to it.
The only change you have to make in your code, once the log is
open, is that you must preceed your entries with a "Level
Number". This, as you will see later, allows you to assign all
log entries a level of importance. Because when you ASSIGN the
log file you also specify the level of entry that is to be
written to the log you can allow users to exclude unimportant
entries. Levels are 1 to 5 with level 1 being the most important
and level 5 being the least (this is based on the Binkley/Opus
log method).
If you assign a log with a level of 3 then only entries with
levels of 3 or below will actually be written to the log, others
will be discarded. To actually assign a level to an entry you
simply preceed it with a number from 1 to 5, for example.
writeln(Log,'1Important: Error ',ErrNum);
writeln(Log,'5Not important at all!');
which is the same as
s := 'Not Important at all!';
writeln(Log,'5',s);
If you do not give an entry a level it will be treated as having
level the same level as the previous entry.
Only entries that start a new line need to be given a level so
that the following has the same effect as the above...
write(Log,#13#10'1Important: Error'); { Start a line }
writeln(Log,ErrNum); { On the same line }
In addition to writing entries to your log file LogDev also echos
entries to the console. As with the log you can set a maximum
level of entry that is to be echoed when you ASSIGNLOG the log.
Entries echoed to the screen are exactly as you wrote them (that
is, they do not have the date/time stamp added).
You can also ASSIGLOG to stdout with ASSIGNLOG(f,''....) just as
you can with Turbo's "Output" file. Then users can redirect log
output. A simple method is to AssignLog(Output,''...) so that all
WRITE/WRITELN statements that do not specify a file are written
via LogDev. This allows you to take an existing program and have
all its output formatted by LogDev (though unless you make some
changes you loose the ablility to control output levels).
However you should NOT echo output to the screen if the primary
log is the console and you should not allow users to redirect
output if the primary log is a disk file (in case they redirect
output to the same file which would lead to a screwed up
disk!!!). Normally LogDev's console output goes to the stderr
handle to avoid this (stderr is not normally redirectable).
Any I/O errors that occur while writing to the log file will be
returned as usual in IORESULT.
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LogDev in use.
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The way it works is this. When assigning a file with AssignLog
you specify a "Level". This is the MINIMUM level of log entry
that will be allowed. Whenever you WRITE a new line to the log
file you preceed the entry with one of the "Entry Levels". IF and
only if the entry has a priority greater than or equal to the
MINIMUM level you set with ASSIGN then the entry is written to
the log otherwise it is ignored.
For example
VAR lf: TEXT;
.....
Logdev_Intro := 'MyProg v1.0';
AssignLog(Lf,'MYPROG.LOG',Binkley,'MPRG',3,0);
{ Log file is MYPOG.LOG
Each entry will be identified by 'MYPRG'
No entrys below level 3 will be written
No echo to screen }
APPEND(Lf); { Append to existing log if any}
IF IORESULT <> 0 THEN REWRITE(Lf); { else new log }
WRITELN(Lf,'1A Serious error'); { WILL go to log }
WRITELN(Lf,'4Progress report'); { will NOT as < Level 3 }
WRITELN(Lf,'5Booring info'); { will NOT as < Level 3 }
CLOSE(Lf);
What happens if the Level Number is missing from the start of a
new line? well there are two possibilities. Normally the line
will be treated as though it had actually had the same level as
the preceeding entry. However the CONSTant
"LogDev_AssumeLastFlag" may be set FALSE by your program and in
this case any line lacking a flag assumes level 5.
Eg.
{ Starts with AssumeLastFlag TRUE }
Logdev_Intro := 'MyProg v1.0';
AssignLog(Lf,'MYPROG.LOG',Binkley,'MPRG',1,0);
{ Log Level 1, only priority 1 messages ('!','*')
will be seen }
APPEND(Lf); { Append to existing log if any}
WRITELN(Lf,'1Eeek, an Error,(Code: ',ErrorCode,')');
WRITELN(lf,'Oh dear, a second error')
WRITELN('Oh dear, another error');
{ Now this line assumes the same flag as the
previous line, "!" with priority 1,
and will be written to the log.
{ Log looks like this
+ 01 Jan 00:10:01 MPRG Begin, MyProg V1.0
! 01 Jan 00:10:01 MPRG Eeek, an error (Code 102)
! 01 Jan 00:10:02 MPRG Oh dear, a second error
! 01 Jan 00:10:03 MPRG And a third error }
AssumeLastFlag := FALSE;
WRITELN(Lf,'1Eeek, an Error (Code: ',ErrorCode,')');
WRITELN(lf,'Oh dear, a second error')
WRITELN(lf,'1And a third error');
{ The second line will default to priority
5 and will not be added to the log}
CLOSE(Lf);
{ Log looks like this
! 01 Jan 00:10:01 MPRG Eeek, an error (Code 102)
! 01 Jan 00:10:03 MPRG And a third error }
If you need to change the logs priority level after opening the
file you can call "SetLogLevel"
Eg: SetLogLevel(f,5,0);
Or you can totally ignore the level of entries and have
everything go into the log by setting "LogDev_IgnoreLevel :=
TRUE"
* You cannot change the level of a log created with an original
level of ZERO because in this case no file was ever actually
created. Level ZERO exists only so that you can give users the
option to switch logging off completely (or perhaps just keep
that which is echoed to the screen).
Echoing output to the screen.
Messages with flag levels >= "ScreenLevel" will be written to the
screen using STDERR (DOS Handle 2). Only your own text will be
written, the flag, date, time and progID added when writing to
the log are NOT sent to the screen.
STDERR is used because it is not (normally) redirectable.
You can make this screen output go to other standard devices by
changing the interface CONST LogDev_ScreenHandle. Default is 2
(STDERR) but you may change it to 1 (STDOUT), 3 (STDAUX) or 4
(STDPRN)
DO NOT use the screen facility if you are assigning the log file
to STDOUT (by using a null file name - see below) as the output
will be garbled.
NEVER use Screen output to STDOUT if assigning the log file also
to STDOUT (ditto see below) because this will corrupt your disk
if the user redirects STDOUT to a file (DOS and your program both
open, write to, and close the same file!!).
Assigning to STDOUT.
This is exactly the same as with Turbo's ASSIGN. If you AssignLog
and give a null file name the file is linked to STDOUT and the
user is able to redirect. ENSURE that, if output is echoed to the
screen it goes to STDERR (the default). Best not to use echo at
all because if the user does NOT redirect STDOUT they will get
garbage on the screen as every character is displayed twice!
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Adding your own log format
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There are no special facilities in the code to allow you to add
your own log format, however it is not hard to do.
1) Add a new type to the LogTypes (INTERFACE block)
type LogTypes = (Binkley,FrontDoor,DBridge,MineOwn);
^^^^^
2) Add a set of flags to be used if you want them
(IMPLEMENTATION)
BinkleyFlags = '!+:# ';
FrontDoorFlags = ' ';
DBridgeFlags = ' ';
MineOwnFlags = '12345';
3) To the CASE Ltyp OF in function LogDateString add code to
return your desired date format (or use the existing one).
4) To the CASE LType OF in function Stamp add code to return
your desired log entry stamp. This function returns the
date/time stamp that preceeds log entries, for instance for
Binkley style logs it returns something like '01 May
04:52:34'
5) Add code to CASE LogType OF in Procedure LogNewLine to set
string "S" to the text required to start a new entry on the
log. This might consist of a flag and a time stamp
appropriately formatted. So for Binkley style logs S is set
to
'+ 01 May 01:45:56 PROGID '
If you are using flag characters the one you want can be
found in FlagChars[LastFlag], Function Stamp amended above
provides the appropriate form of time stamp.
6) In Function LogOpen is a CASE Params(UserData).LogType OF
which adds any automatic entries to a newly opened log. If
you want to do this add your own code to do it. Note that
for Binkley style logs the variable Mode (part of a
TextRec) is used to determine if the file was opened by an
APPEND call (Mode = fminout) so as to add a blank line to
an existing log.
7) If you are using flag characters add code to the CASE
LogType OF in procedure AssignLog. You must set FlagChars
equal to your flag characters defined earlier.
8) If you want to do anything special when CLOSEing a log add
code to Procedure LogClose (see the example used by Binkley
log type).
That should about do it. Note though that I have not actually
tested the above suggestions (should be right though).
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| 
M.P.B. Cole