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.title ##########Conversion TOPS10/20 COBOL-74 to VAX-11 COBOL
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.ts 10,20,30,40,50,60,70
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TOPS10/20 COBOL-74 to VAX-11 COBOL
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.s 3.f;These notes can be usefull and helpfull tools with other
conversions to VAX-11 COBOL.
.br;The remarks were sampled from the following projects:
.ls '='.le;Conversion from TOPS20 COBOL-74 to VAX-11 COBOL, done by
Jude_ Braden, Dublin-office. (EASINET MAIL-address: DUB01::BRADEN)
.le;Conversion from TOPS10 COBOL-74 to VAX-11 COBOL, done by
Jan_ Postmus, Utrecht-office. (EASINET MAIL-address: UTR01::POSTMUS)
.els;Please contact one of the above mentioned persons, concerning
remarks on projects like these.
.hl 1 GENERAL REMARKS
.hl 2 File Specifications
.ls '='.le;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"'.
.le;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.
.br;For more information, see Chapter "I/O Processing" in "VAX-11 COBOL
User's Guide".
.els.hl 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).
.br;See also remarks on 'INITIALIZE', 'READ' and 'WRITE'.
.hl 2 Quotes
All single quotes (_ '_ ) should be changed to double quotes (_ "_ ).
.hl 2 Spaces with '=' and ','
VAX-11 COBOL likes to see spaces around '=' and after ','.
.hl 1 IDENTIFICATION DIVISION
.hl 2 IDENTIFICATION DIVISION
VAX-11 COBOL wants the name 'IDENTIFICATION_ DIVISION' full,
not short 'ID_ DIVISION'.
.hl 1 ENVIRONMENT DIVISION
.hl 2 SOURCE-COMPUTER
Of course this has to be changed to 'VAX-11'.
.hl 2 OBJECT-COMPUTER
.ls '='.le; Of course this has also to be changed to 'VAX-11'.
.le;'MEMORY' clause is for documentation only on VAX, in TOPS COBOL
it is presently ignored.
.els.hl 2 SPECIAL-NAMES
.ls '='.le;Special attention should be taken with the SPECIAL-NAMES SECTION.
.le;Change 'CHANNEL (1)' into 'C01' for use of skip output to top-of-form.
.els.hl 2 SELECT
.ls '='.le;The SELECT statement may have to be changed for VAX.
.le;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:
.nf.s 1.ls;'ASSIGN TO DISK01' into 'ASSIGN TO "DISK01:"'
.els.f;See also the remarks about File Specifications.
.le;The 'RECORDING MODE' in the file description has been discontinued,
it cannot be used on VAX.
.els.hl 1 DATA DIVISION
.hl 2 FD
.ls '='.le;'BLOCK CONTAINS 0 RECORDS', used on TOPS10 to indicate unblocked
mode, cannot be used on VAX, this statement can be deleted.
.le;VAX COBOL likes to see a 'RECORD CONTAINS' clause, when 'BLOCK CONTAINS'
is used.
.le;'VALUE OF IDENTIFICATION' should be changed to 'VALUE OF ID'.
.le;With respect to 'VALUE OF ID', see also the remarks about File
Specifications.
.le;The 'RECORDING MODE' in the file description has been discontinued,
it cannot be used on VAX.
.le;'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).
.els.hl 2 LINE-COUNTER/PAGE-COUNTER
'LINE-COUNTER' and 'PAGE-COUNTER' are reserved names in VAX-11 COBOL,
change these names if present in code.
.hl 2 OCCURS
.ls '='.le;You may need to check the use of 'REDEFINES' with 'OCCURS'.
.le;VAX does not allow the use of 'OCCURS' with a level-number 01 or 77,
TOPS10/20 COBOL-74 does allow this.
.le;When specifying key and index in the 'OCCURS' clause, the VAX wants it
in the order: key first, then index, like:
.nf.s 1.ls;ASCENDING KEY IS ......
INDEXED BY ......
.els.f.els.hl 2 REDEFINES
.ls '='.le;Make sure that the REDEFINES item is not bigger than the
item REDEFINED.
.le;You may need to check the use of 'REDEFINES' with 'OCCURS'.
.els.hl 2 SIGN
When using the 'SIGN' clause you have to include the character 'S'
in your numeric data description picture.
.hl 2 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.
.hl 1 PROCEDURE DIVISION
.hl 2 Paragraph header after 'PROCEDURE DIVISION'
VAX COBOL likes to see a paragraph header directly after the 
'PROCEDURE DIVISION' statement.
.hl 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:
.ls '='.le;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.
.le;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.
.els.hl 2 Remarks on Testing for Certain Values
.ls '='.le;VAX does not like the testing of a numeric field for spaces.
Use 'IF FIELD NOT NUMERIC' instead.
.le;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".
.le;When a group-item exists out of several signed numeric items, checking
against 'ZERO' cannot be performed.
.els.hl 2 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.
.br;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 into numeric, including some basic checking. Both called
after accepting the data from the terminal.
.hl 2 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:
.ls '=';.le;from a file, p.g. : 'COPY ABCD' - code from file ABCD.LIB
is inserted.
.le;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.
.le;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.
.els.hl 2 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.
.hl 2 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:
.nf.lt;
  TOPS COBOL statement:
      DISPLAY " TOTAL " INDEX.

  declare display-field, and change code into:
      DISPL    PIC 99.

      SET DISPL TO INDEX.
      DISPLAY " TOTAL " DISPL.

.el.f;Use 'MOVE INDEX TO DISPL' instead of 'SET DISPL TO INDEX', in case
an integer is involved.
.hl 2 EQUALS
The word 'EQUALS' should be changed to ' = ' or 'IS EQUAL'.
.hl 2 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.
.hl 2 INITIALIZE
.ls '='.le;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.
.le;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:
.ls '-'.le;Using 'OCCURS' clause with 'DEPENDING' phrase in the field to be
initalized, is not allowed.
.le;It does not work on 'index data items'.
.le;Items declared 'FILLER' are not affected. When they have to be cleared
too, use 'MOVE SPACES' and 'INITIALIZE'.
.le;Mind, the contents, set up with 'VALUE' phrase in the DATA DIVISION,
is cleared too, except for items defined 'FILLER'.
.le;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.
.els.els.hl 2 INSPECT
The 'INSPECT' verb requires that the compare-value and the replace-value
be of the same type (i.e. Numeric, Alphabetic, etc.).
.hl 2 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').
.hl 2 READ
.ls '='.le;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'.
.le;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.
.els.hl 2 SEARCH
.ls '='.le;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:
.nf.s 1.ls;'WHEN table-element = value'
.els.f.le;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.
.els.hl 2 SORT
Only section names are allowed by VAX-11 COBOL in 'INPUT PROCEDURE'
and 'OUTPUT PROCEDURE'.
.hl 2 WRITE
.ls '='.le;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.
.le;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.
.els.hl 1 Index Handling
During the Utrecht project, this showed to be a very difficult matter,
causing a lot of conversion problems.
.hl 2 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.
.hl 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:
.ls '='.le;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.
.br;Change these, when indices are involved, like:
.nf.lit;
  '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'
.el.f.le;'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.
.le;Using indices in the 'DISPLAY' statement, to show their value,
is not allowed in VAX COBOL, see remark concerning 'DISPLAY'.
.els.hl 1 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.
.br;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.
.br;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.
.hl 2 Passing value to $STATUS (Error Exit)
When using 'STOP RUN', automatically $STATUS will get the value "1",
indicating normal, successfull exit.
.br;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:
.s 1.ls;CALL "SYS$EXIT" USING BY VALUE WK-ERROR.
.els;'WK-ERROR' has to be defined as numeric/computational (it has to
be an integer), holding the appropiate error code value.
.br;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).
.hl 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".
.br; In short the procedure is:
.ls.le;Create a message source file, using a text editor, called p.g.
'OWNMESS.MSG'.
.le;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.
.le;Link the object file (DCL-command: $_ LINK), creating an
non-executable message file 'OWNMESS.EXE'.
.le;Tell DCL to look into this message file, by typing the DCL-command
$_ SET_ MESSAGE_ OWNMESS
.le;Use the DCL-command $_ SHOW_ SYMBOL_ 'code' to investigate the
value of the several codes.
.le;Use these decimal values in the program(s) to specify the particular
error-code.
.els.hl 2 Remarks concerning Message File
Linking the message object file to the program is possible (see the
"Message Utility" manual), but implementation can be difficult, as
seen during the Utrecht project. To make it flexible, the following
could be a good way (as done in the Utrecht project):
.ls '='.le;Own message file was created, according the above
mentioned procedure.
.le;The programs were updated, that in case of a detected error,
the program called a subroutine, passing through a normal numeric value,
indicating the error, but according an internal list.
.le;The called subroutine took care about the translation of this internal
code into the correct error message code, according the message file.
After translation this subroutine also performed the call to 'SYS$EXIT'.
.els;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.
.hl 1 Runtime error conditions
.hl 2 '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.
.hl 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.
.br;Also moving 'LOW-VALUES' to group-items
caused this error condition, during the Utrecht project.
.s 3.c
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