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tools/cbldoc1/cbl102vax.txt
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Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 1
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TOPS10/20 COBOL-74 to VAX-11 COBOL
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These notes can be usefull and helpfull tools with other
conversions to VAX-11 COBOL.
The remarks were sampled from the following projects:
= Conversion from TOPS20 COBOL-74 to VAX-11 COBOL, done by
Jude Braden, Dublin-office. (EASINET MAIL-address:
DUB01::BRADEN)
= Conversion from TOPS10 COBOL-74 to VAX-11 COBOL, done by
Jan Postmus, Utrecht-office. (EASINET MAIL-address:
UTR01::POSTMUS)
Please contact one of the above mentioned persons, concerning
remarks on projects like these.
1.0 GENERAL REMARKS
1.1 File Specifications
= The periode between file-name and file-ext in file-spec, has
to be specified in VAX COBOL (was omitted in TOPS10 COBOL).
The specification 'VALUE "COB DAT"' has to be changed into
'VALUE "COB.DAT"'.
= The file-specification passed to VAX/VMS on runtime, is a
combination of 'ASSIGN file-spec' ('SELECT' statement) and
'VALUE OF ID file-spec' ('FD' specification). A file-spec
field given with 'VALUE OF ID' clause overrides the
corresponding field in the 'ASSIGN' clause.
For more information, see Chapter "I/O Processing" in "VAX-11
COBOL User's Guide".
1.2 Clearing Of Records
Record clearing, prior to reading, or after writing, is not
handled by VAX COBOL the way it is done by TOPS COBOL. One of
the best is, use the 'INITIALIZE' statement, if necessary
together with 'MOVE' instruction(s).
See also remarks on 'INITIALIZE', 'READ' and 'WRITE'.
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 2
1.3 Quotes
All single quotes ( ' ) should be changed to double quotes ( " ).
1.4 Spaces With '=' And ','
VAX-11 COBOL likes to see spaces around '=' and after ','.
2.0 IDENTIFICATION DIVISION
2.1 IDENTIFICATION DIVISION
VAX-11 COBOL wants the name 'IDENTIFICATION DIVISION' full, not
short 'ID DIVISION'.
3.0 ENVIRONMENT DIVISION
3.1 SOURCE-COMPUTER
Of course this has to be changed to 'VAX-11'.
3.2 OBJECT-COMPUTER
= Of course this has also to be changed to 'VAX-11'.
= 'MEMORY' clause is for documentation only on VAX, in TOPS
COBOL it is presently ignored.
3.3 SPECIAL-NAMES
= Special attention should be taken with the SPECIAL-NAMES
SECTION.
= Change 'CHANNEL (1)' into 'C01' for use of skip output to
top-of-form.
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 3
3.4 SELECT
= The SELECT statement may have to be changed for VAX.
= To be able to use logical names with 'ASSIGN' and 'VALUE OF
ID' the same as implemented on TOPS, put the logical name in
quotes and use a colon, p.g. change:
'ASSIGN TO DISK01' into 'ASSIGN TO "DISK01:"'
See also the remarks about File Specifications.
= The 'RECORDING MODE' in the file description has been
discontinued, it cannot be used on VAX.
4.0 DATA DIVISION
4.1 FD
= 'BLOCK CONTAINS 0 RECORDS', used on TOPS10 to indicate
unblocked mode, cannot be used on VAX, this statement can be
deleted.
= VAX COBOL likes to see a 'RECORD CONTAINS' clause, when
'BLOCK CONTAINS' is used.
= 'VALUE OF IDENTIFICATION' should be changed to 'VALUE OF ID'.
= With respect to 'VALUE OF ID', see also the remarks about
File Specifications.
= The 'RECORDING MODE' in the file description has been
discontinued, it cannot be used on VAX.
= 'USER-NUMBER' to specify [PPN] is unknown on VAX, it has to
be deleted. Take care about directory-specification through
file-spec or logical name with 'ASSIGN' or 'VALUE OF ID' (see
remarks about File Specifications).
4.2 LINE-COUNTER/PAGE-COUNTER
'LINE-COUNTER' and 'PAGE-COUNTER' are reserved names in VAX-11
COBOL, change these names if present in code.
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 4
4.3 OCCURS
= You may need to check the use of 'REDEFINES' with 'OCCURS'.
= VAX does not allow the use of 'OCCURS' with a level-number 01
or 77, TOPS10/20 COBOL-74 does allow this.
= When specifying key and index in the 'OCCURS' clause, the VAX
wants it in the order: key first, then index, like:
ASCENDING KEY IS ......
INDEXED BY ......
4.4 REDEFINES
= Make sure that the REDEFINES item is not bigger than the item
REDEFINED.
= You may need to check the use of 'REDEFINES' with 'OCCURS'.
4.5 SIGN
When using the 'SIGN' clause you have to include the character
'S' in your numeric data description picture.
4.6 USAGE IS INDEX
The VAX reacted different as the TOPS did, with respect to items
declared 'USAGE IS INDEX'. All references in the code to these
index-items (like 'SET', 'MOVE', subscripts, indexing), were
rejected by the compiler. Changed the definition from 'USAGE
INDEX' into 'PICTURE 9(5) COMPUTATIONAL'. Technically, the item
is not an index-item, then. See also the section 'INDEX
HANDLING' further on.
5.0 PROCEDURE DIVISION
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 5
5.1 Paragraph Header After 'PROCEDURE DIVISION'
VAX COBOL likes to see a paragraph header directly after the
'PROCEDURE DIVISION' statement.
5.2 Group-items
VAX COBOL strictly treates a group-item as alpha-numeric,
regardless how the subsequent items are declared. Some points to
take care for, concerning group-items:
= Because treated as alpha-numeric, moving from a field
declared numeric with sign and/or decimal point, p.g.
S9(13)V9(5), to a group-item, does work different as it does
on TOPS COBOL.
= When a group-item exists out of several signed numeric items,
checking the group-item against 'ZERO' cannot be performed,
each item has to be checked individually.
5.3 Remarks On Testing For Certain Values
= VAX does not like the testing of a numeric field for spaces.
Use 'IF FIELD NOT NUMERIC' instead.
= When testing items, they have to be of the same type, VAX is
very strict on this, so testing a field, defined as 'PICTURE
X(8)', against a numeric constant nnn, is not allowed, while
TOPS COBOL will take care about translation. In this case
the numeric constant has to placed between double quotes, as
"nnn".
= When a group-item exists out of several signed numeric items,
checking against 'ZERO' cannot be performed.
5.4 ACCEPT
When using the 'ACCEPT' statement, VAX COBOL always treates the
receiving field as an alpha-numeric field, and justifies the
received data always left (extended with spaces to the right),
even when the field is declared 'JUSTIFIED RIGHT' or numeric.
One of the ways of accepting numeric values or get the data right
justified, is to create subroutines to handle these situations.
During the Utrecht project, it was necessary to make a subroutine
to handle alpha-numeric input and get it right justified, and
another subroutine to receive alpha-numeric data and translate it
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 6
into numeric, including some basic checking. Both called after
accepting the data from the terminal.
5.5 COPY
Care should be taken, because there are differences in using
'COPY' in VAX COBOL or in TOPS COBOL. When using 'COPY'
statement in TOPS COBOL, always code from a source-library,
created with LIBARY, is taken. In VAX COBOL, there are 3
possibilities:
= from a file, p.g. : 'COPY ABCD' - code from file ABCD.LIB
is inserted.
= from a library, p.g. : 'COPY ABCD FROM BCDE' - code from
text module ABCD in library BCDE.TLB is inserted; library
should be a text library, created by VAX LIBRARIAN.
= record definition from CDD, p.g. : 'COPY ABCD FROM
DICTIONARY' - the record definition is inserted from Common
Data Dictionary; only record definitions can be used this
way.
5.6 CLOSE
'CLOSE file-name WITH DELETE' is unknown on VAX, deleting a file,
in case of a detected error in the program, should be handled
outside the program. See the remarks concerning "Program
Detected Errors and Handling.
5.7 DISPLAY
In VAX COBOL, index data items and integers
(numeric/computational), cannot be used in 'DISPLAY' statement
straight away, they have to be moved to a field declared for
DISPLAY USAGE. Example:
TOPS COBOL statement:
DISPLAY " TOTAL " INDEX.
declare display-field, and change code into:
DISPL PIC 99.
SET DISPL TO INDEX.
DISPLAY " TOTAL " DISPL.
Use 'MOVE INDEX TO DISPL' instead of 'SET DISPL TO INDEX', in
case an integer is involved.
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 7
5.8 EQUALS
The word 'EQUALS' should be changed to ' = ' or 'IS EQUAL'.
5.9 HIGH-VALUES/LOW-VALUES
These values can be used, as long as testing is done against the
same value the field was previously set to. Resetting fields
with 'LOW-VALUES' can cause trouble, better use 'INITIALIZE' or
'MOVE ZERO' to reset fields.
5.10 INITIALIZE
= It is advised to use the 'INITIALIZE' verb, where possible
and sensible, as spaces and zeroes are not regarded the same
on VAX. We found during our conversions that spaces were
moved to numeric fields and zeroes to alphabetic fields quite
regularily.
= However, there are some points to regard, using the
'INITIALIZE'. It works very nice for normal records and
fields, also when using 'OCCURS' without 'DEPENDING',
computational fields, etc. Care should be taken with the
following:
- Using 'OCCURS' clause with 'DEPENDING' phrase in the
field to be initalized, is not allowed.
- It does not work on 'index data items'.
- Items declared 'FILLER' are not affected. When they have
to be cleared too, use 'MOVE SPACES' and 'INITIALIZE'.
- Mind, the contents, set up with 'VALUE' phrase in the
DATA DIVISION, is cleared too, except for items defined
'FILLER'.
- Take care with fields which are REDEFINED. When the
field, to be initialized, is REDEFINED, the instruction
works O.K., but when one or more sub-ordinate items have
'REDEFINES', 'INITIALIZE' does not affect them.
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 8
5.11 INSPECT
The 'INSPECT' verb requires that the compare-value and the
replace-value be of the same type (i.e. Numeric, Alphabetic,
etc.).
5.12 MOVE
Special care should be taken with 'MOVE SPACES' and 'MOVE ZERO',
use 'INITIALIZE' where possible and sensible, instead of these
instructions (see also the remarks concerning 'INITIALIZE').
5.13 READ
= Using 'AT END' clause, like 'READ file-name AT END
statement', the statements can only be "imperative", so no
'IF' can be used. If necessary, create a paragraph to handle
the 'IF' after 'AT END'.
= Care should be taken with record clearing, prior to a 'READ'
operation. VAX COBOL does not always clear fields, better
take care of it yourself, by using the 'INITIALIZE', but mind
the specifics concerning this statement.
5.14 SEARCH
= Testing a table element in the 'WHEN' clause, VAX COBOL
expects the element directly behind 'WHEN', while TOPS COBOL
allows to have them swapped. For example, VAX COBOL wants:
'WHEN table-element = value'
= More complex conditions (like using ' < ', ' > ', etc.) in
the 'WHEN' clause, were rejected for use in the 'SEARCH ALL'
statement. It was allowed for the 'SEARCH' statement.
5.15 SORT
Only section names are allowed by VAX-11 COBOL in 'INPUT
PROCEDURE' and 'OUTPUT PROCEDURE'.
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 9
5.16 WRITE
= Take care about the clearing of the record, after writing and
before filling it, specifically when partly filled, because
VAX COBOL might not clear it for you. One of the best ways
is to use the 'INITIALIZE' verb, but mind the specifics about
this instruction.
= In case the total conversion included also conversion from
TOPS10/20 COBOL-68 to -74, mind the 'ADVANCING BEFORE 1
LINE'. Because default differences between -68 and -74,
changes had to be made for ASCII files, not for SIXBIT. On
VAX COBOL, SIXBIT is unknown, therefore mind the 'WRITE'
statement, for files, which use to be SIXBIT in TOPS COBOL,
and on VAX in ASCII.
6.0 INDEX HANDLING
During the Utrecht project, this showed to be a very difficult
matter, causing a lot of conversion problems.
6.1 USAGE IS INDEX
The VAX reacted different as the TOPS did, with respect to items
declared 'USAGE IS INDEX' (in the DATA DIVISION). All references
in the code to these items ('SET', 'MOVE', subscripts, etc.) were
rejected by the compiler. Changed the definition from 'USAGE
INDEX' into 'PICTURE 9(5) COMPUTATIONAL', which worked O.K.
then. In this case, the item was not an index-item, but an
integer.
6.2 Manipulating Index
Items could be proper indices, by having them declared with the
clause 'INDEXED BY .....' in the 'OCCURS' statement. With
respect to manipulation, the following should be regarded:
= TOPS COBOL allows to handle indices with normal 'MOVE', 'ADD'
and 'SUBTRACT'. VAX-11 COBOL is more strictly, only the
'SET' instruction has to be used.
Change these, when indices are involved, like:
'MOVE x TO index' into 'SET index TO x'
'ADD x TO index' into 'SET index UP BY x'
'SUBTRACT x FROM index' into 'SET index DOWN BY x'
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 10
= 'MOVE 0 TO index' was allowed in TOPS COBOL, VAX COBOL does
not allow to set an index to '0', use 'SET index TO 1' and
change the code to be able to use it this way.
= Using indices in the 'DISPLAY' statement, to show their
value, is not allowed in VAX COBOL, see remark concerning
'DISPLAY'.
7.0 PROGRAM DETECTED ERRORS AND HANDLING
By displaying the error character, while running the program in
BATCH or MIC under TOPS, an error condition could be signalled,
causing the stream to be aborted.
The command sequence in VAX-11 does not have a simular facility,
but VAX/VMS offers the possibility to pass codes through $STATUS,
indicating normal end (value "1") or certain error-codes.
Standard error-codes can be used, or own codes can be created by
the user, specifying the $STATUS value, these codes can be
passed, and examined in the COM sequence.
7.1 Passing Value To $STATUS (Error Exit)
When using 'STOP RUN', automatically $STATUS will get the value
"1", indicating normal, successfull exit.
In case an abnormal end, p.g because of a program detected error,
has to be passed through to $STATUS, the system subroutine
'SYS$EXIT' can be used. It is called by:
CALL "SYS$EXIT" USING BY VALUE WK-ERROR.
'WK-ERROR' has to be defined as numeric/computational (it has to
be an integer), holding the appropiate error code value.
No return to the program is made, the effect is the same as 'STOP
RUN', except the value of 'WK-ERROR' is placed into $STATUS.
Unfortunately in COBOL no hexa-decimal values for constants can
be used, so the decimal value of the code has to be known
(DCL-command: $ SHOW SYMBOL).
7.2 Creating Own Error Codes And Messages
For information, how to create own messages, see the manual
"VAX-11 Utilities Reference Manual", Chapter "Message Utility".
In short the procedure is:
1. Create a message source file, using a text editor, called
p.g. 'OWNMESS.MSG'.
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 11
2. Compile the source file with the message-compiler
(DCL-command: $ MESSAGE), creating an object file
'OWNMESS.OBJ'. Also a listing with the codes, including the
hexa-decimal values, can be obtained.
3. Link the object file (DCL-command: $ LINK), creating an
non-executable message file 'OWNMESS.EXE'.
4. Tell DCL to look into this message file, by typing the
DCL-command $ SET MESSAGE OWNMESS
5. Use the DCL-command $ SHOW SYMBOL 'code' to investigate the
value of the several codes.
6. Use these decimal values in the program(s) to specify the
particular error-code.
7.3 Remarks Concerning Message File
Linking the message object file to the program is possible (see
the "Message Utility" manual), but implementation can be
difficult, as seen during the Utrecht project. To make it
flexible, the following could be a good way (as done in the
Utrecht project):
= Own message file was created, according the above mentioned
procedure.
= The programs were updated, that in case of a detected error,
the program called a subroutine, passing through a normal
numeric value, indicating the error, but according an
internal list.
= The called subroutine took care about the translation of this
internal code into the correct error message code, according
the message file. After translation this subroutine also
performed the call to 'SYS$EXIT'.
In case the message file has to be updated, very likely on the
long run, it is not necessary to update and recompile all
programs, possibly updating and recompiling of the error handling
subroutine is the only necessity.
8.0 RUNTIME ERROR CONDITIONS
Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL Page 12
8.1 'DIVISION BY 0' Error
A 'DIVISION BY 0' error occurred very frequently during the
Dublin project. Incorporated therefore an appropriate 'IF'
statement, which rectified the error.
8.2 'INVALID DECIMAL DATA' Error Condition
'INVALID DECIMAL DATA' error condition occurred very frequently
also. This error was generated because spaces were moved to
numerics and zeroes to alphabetic fields.
Also moving 'LOW-VALUES' to group-items caused this error
condition, during the Utrecht project.
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