cobol
Dichiarazione ALTER

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La tanto amata dichiarazione ALTER. Cambia l'obiettivo di un paragrafo GO TO.

Non fa più parte dello standard COBOL, ancora supportato da molti compilatori per ragioni di compatibilità con le versioni precedenti. (Il diagramma della sintassi è disattivato per mostrare che questo non è più COBOL standard).

inserisci la descrizione dell'immagine qui

Un esempio forzato usando ALTER

 identification division.
 program-id. altering.
 date-written. 2015-10-28/06:36-0400.
 remarks. Demonstrate ALTER.

 procedure division.
 main section.

*> And now for some altering.
 contrived.
 ALTER story TO PROCEED TO beginning
 GO TO story
 .

*> Jump to a part of the story
 story.
 GO.
 .

*> the first part
 beginning.
 ALTER story TO PROCEED to middle
 DISPLAY "This is the start of a changing story"
 GO TO story
 .

*> the middle bit
 middle.
 ALTER story TO PROCEED to ending
 DISPLAY "The story progresses"
 GO TO story
 .

*> the climatic finish
 ending.
 DISPLAY "The story ends, happily ever after"
 .

*> fall through to the exit
 exit program.

Con un campione di prova di 

prompt$ cobc -xj -debug altering.cob
This is the start of a changing story
The story progresses
The story ends, happily ever after

prompt$ COB_SET_TRACE=Y ./altering
Source:     'altering.cob'
Program-Id: altering         Entry:     altering               Line: 8
Program-Id: altering         Section:   main                   Line: 8
Program-Id: altering         Paragraph: contrived              Line: 11
Program-Id: altering         Statement: ALTER                  Line: 12
Program-Id: altering         Statement: GO TO                  Line: 13
Program-Id: altering         Paragraph: story                  Line: 17
Program-Id: altering         Paragraph: beginning              Line: 22
Program-Id: altering         Statement: ALTER                  Line: 23
Program-Id: altering         Statement: DISPLAY                Line: 24
This is the start of a changing story
Program-Id: altering         Statement: GO TO                  Line: 25
Program-Id: altering         Paragraph: story                  Line: 17
Program-Id: altering         Paragraph: middle                 Line: 29
Program-Id: altering         Statement: ALTER                  Line: 30
Program-Id: altering         Statement: DISPLAY                Line: 31
The story progresses
Program-Id: altering         Statement: GO TO                  Line: 32
Program-Id: altering         Paragraph: story                  Line: 17
Program-Id: altering         Paragraph: ending                 Line: 36
Program-Id: altering         Statement: DISPLAY                Line: 37
The story ends, happily ever after
Program-Id: altering         Statement: EXIT PROGRAM           Line: 41
Program-Id: altering         Exit:      altering
prompt$

Vedi http://open-cobol.sourceforge.net/faq/index.html#alter per maggiori dettagli.



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