Re: DOU/DOW for READ Loops (My final word)

Simon, what about:

  C          Key          Chain   File
  C                       If      &found
  C                       DOU     %EOF
  C               stuuff
  C                       Read    File
  C                       EndDo
  C                       EndIf


_______________________
Booth Martin
boothm@earth.goddard.edu
http://www.spy.net/~booth
_______________________




"Simon Coulter" <shc@flybynight.com.au>
Sent by: owner-rpg400-l@midrange.com
04/20/2000 02:31 AM
Please respond to RPG400-L

 
        To:     RPG400-L@midrange.com
        cc: 
        Subject:        DOU/DOW for READ Loops (My final word)



OK Dan,

You asked for it!
>Damnit Simon, you just had to, didn't you!  OK, _WHY_ is DOU/IF wrong? 
None
>of this, "it just is", stuff.  You, of all people, are not a man of few
>words.  (New thread, please.)

I'm not planning to continue this discussion.  No one can persuade me that 
DOU/IF is 
correct so don't try.  I am not expecting to persuade anyoune in that camp 
they are wrong. 
Often times people are wrong and simply cannot see it.  Here is my 
reasoning, think it 
through and decide for yourselves.

0/ Well, it is "just wrong".  Your gut should tell you that!

1/ The most obvious objection is that DOU always executes at least once. 
Since there is 
no guarantee that the file contains any data (or at least no data that 
matches your search 
criteria), and you shouldn't assume it does, your loop may not execute at 
all therefore a 
DOW is appropriate.

2/ DOU forces an unneccesary additional test for the same condition -- 
regardless of the 
'speed' of the new systems, using excess resources is inefficient and 
sloppy.

3/ In this case DOU results in contrived code -- what you are attempting 
to code is a DO 
FOREVER then IF EOF LEAVE.  If that's what you want then code it as such. 
Although RPG 
does not provide direct support for that construct (and I don't like it 
anyway) you can 
code:

                 'Homer'                 DOUEQ           'Doh'
                                 READ            FileFmt         99
                 *IN99           IFEQ            *ON
                                 LEAVE
                                 ENDIF
                                 do stuff here
                                 ENDDO

or in RPGIV

                                 DOU             'Homer' = 'Doh'
                                 READ            FileFmt
                                 IF              %EOF
                                 LEAVE
                                 ENDIF
                                 do stuff here
                                 ENDDO

In each of these cases the loop is required to run once to determine if 
data is available 
thus a DOU is used.  This seems to me rather artificial.  What you really 
want is WHILE 
DATA DO construct. 

 Languages that do provide proper support for this result in clean, 
concise, elegant code. 
For example in C one could write:

while ((nbrBytesRead = fread(rcdBuffer, sizeof(char), sizeof(rcdBuffer), 
streamFilePtr )) 
> 0 )
{
                 /* Do stuff here */
}

This is more elegant because the code states that I want to loop until 
nothing was read 
from the file.  The intent is obvious and it's clean -- I don't need 
clumsy LEAVE or break 
statements but note that the DOU construct would not work without the 
extra IF test.

do 
{
                 nbrBytesRead = fread(rcdBuffer, sizeof(char), 
sizeof(rcdBuffer), streamFilePtr );
                 /* Do stuff here */
} while ( nbrBytesRead  > 0 ) 

would fail and needs to be 

do 
{
                 nbrBytesRead = fread(rcdBuffer, sizeof(char), 
sizeof(rcdBuffer), streamFilePtr );
                 if (nbrBytes <= 0) break;
                 /* Do stuff here */
} while ( nbrBytesRead  > 0 ) 

which is quite obviously ugly as well as inefficient.  If you don't like 
the break 
statement then recode the if test:

do 
{
                 nbrBytesRead = fread(rcdBuffer, sizeof(char), 
sizeof(rcdBuffer), streamFilePtr );
                 if (nbrBytes > 0) 
                 {
                                 /* Do stuff here */
                 }
} while ( nbrBytesRead  > 0 ) 

Now the double test for nbrBytesRead should be making you cringe.

We know that RPG doesn't directly support reading data and testing the 
result of the read 
in a single line of code but there is no reason why you can't write I/O 
procedures in RPG 
IV that return a boolean or count then you could code something like:

                 DOW             (getData(FileFmt))
                 do stuff here
                 ENDDO

Now is that elegant or what!  Of course, you would want to give a little 
thought to the 
procedure names (well, quite a lot of thought actually -- names are very 
important but 
that's another topic).

4/ As David Keck wrote on MIDRANGE-L -- just do what Simon says! QED

Now for my next exercise in futility I shall debate the merits of using 
the Format name 
rather than the File name on I/O statements ....  :)

Regards,
Simon Coulter.

«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»
«» FlyByNight Software         AS/400 Technical Specialists       «»
«» Eclipse the competition - run your business on an IBM AS/400.  «»
«»                                                                «»
«» Phone: +61 3 9419 0175      Mobile:
61 0411 091 400           «»
«» Fax:   +61 3 9419 0175      mailto: shc@flybynight.com.au      «»
«»                                                                «»
«» Windoze should not be open at Warp speed.                      «»
«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»«»
+---
| This is the RPG/400 Mailing List!
| To submit a new message, send your mail to RPG400-L@midrange.com.
| To subscribe to this list send email to RPG400-L-SUB@midrange.com.
| To unsubscribe from this list send email to RPG400-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: 
david@midrange.com
+---




+---
| This is the RPG/400 Mailing List!
| To submit a new message, send your mail to RPG400-L@midrange.com.
| To subscribe to this list send email to RPG400-L-SUB@midrange.com.
| To unsubscribe from this list send email to RPG400-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---