问题
On this read statement below couldn't it be made into the form of the following? I think personaly it might be easier to understand and read.
Basically the read statement is simply reading through a file and making decision on which paragraph performs should be executed. It probably is difficult to see exaclty what the program does but what I was really interested to know was if you can change the read to a different format as listed below.
READ DATA-FILE AT END ...do some code NOT AT END ...do code that is below END-READ.
Class:
INIT-READ.
READ C AT END
GO TO EOJ.
IF C-ID = ' ' AND C-S = 'P'
GO TO I-R
END-IF.
IF CID = ' ' AND C-S = 'D'
IF F = 'Y'
MOVE 'N' TO F
MOVE 'your text here' TO RPT-ID
MOVE A TO H6
MOVE B TO H7
PERFORM PA THRU H-A-X
END-IF
PERFORM WD-CLAIM THRU W-X
GO TO I-R
END-IF.
PERFORM N-V THRU N-V-X.
回答1:
At the bottom of a discussion thread, captured in the GNU Cobol FAQ, http://opencobol.add1tocobol.com/gnucobol/#performing-forever Roger While mentioned a pretty nice idiom for READ control without paragraphs.
One thing that I saw on earlier posts to the newsgroup cobol was
What is the need/justification for an empty inline perform group.
ie. PERFORM ... END-PERFORM
None of the discussions then realized that there is a - EXIT PERFORM [CYCLE]
Therefore, it is a method to to define an exit condition without having paragraphs.
ie. (very simply)
PERFORM
READ xxx
AT END
EXIT PERFORM
END-READ
MOVE something TO somewhere
END-PERFORM
.. test xxx status and somewhere
There are, of course, other variations. Basically, it means that you code without using section/paragraphs. (Recommended, if only from performance point of view)
Note that the CYCLE option offers interesting possibilities.
Roger
回答2:
Have a look here. COBOL read/store in table. for a way of avoiding GO TO, and even the AT END/NOT AT END. No END-READ needed either.
To avoid the AT END/NOT AT END, simply use the File Status, which you should already be using anyway to check that all IO operations were successful. For an input file, READ will give a file status of 10 when end-of-file is detected.
Use an 88 on your file status. So you can say things like END-OF-PAYMENTS-TRANSACTIONS.
Then, to process your file, you use a "priming read". This is a read outside the loop.
priming read
processing-loop until END-OF-PAYMENTS-TRANSACTIONS
do the processing
read
EXIT PERFORM (and some other EXIT options) is not available in all COBOLs currently. Be aware that if you are part of a large team and put an EXIT PERFORM in your program you will likely find several EXIT PERFORMs in the same block of code within a couple of years. So they may have well been GO TOs all along. The new EXIT options are just a way of have a GO TO which is spelled differently. OK, a little tongue-in-cheek, but there we go.
Of course, the priming read and read above both PERFORM a single paragraph to do the actual read and check the validity of the io (file status zero or 10 is OK, else a problem).
Be careful about considering avoiding PERFORM paragraph/SECTION for "performance". Write for clarity unless performance is critical. With IBM's Enterprise COBOL, using OPT, PERFORM code can be "inlined" anyway.
来源：https://stackoverflow.com/questions/20641281/cobol-read-statement-format-can-it-be-redone-a-different-way