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The ALLBASE/SQL COBOL Preprocessor
The ALLBASE/SQL COBOL preprocessor is specifically for COBOL II/XL
programs.
Figure 1-2 summarizes the four main preprocess-time events:
* Syntax checking of SQL commands and host variable declarations.
* Creation of compilable files: one modified source code file and
two include files.
* Creation of an installable module.
* Storage of a module in the system catalog.
Click here to view figure.
Figure 1-2. Preprocess Time Events
Effect of Preprocessing on Source Code
The COBOL preprocessor scans the source code for SQL commands. If the
syntax of an SQL command is correct, the preprocessor converts the
command into compilable COBOL statements that call ALLBASE/SQL external
procedures at run time. During preprocessing, for example, the following
SQL command is converted to modified source code.
EXEC SQL SELECT PARTNUMBER, PARTNAME, SALESPRICE
INTO :PARTNUMBER,
:PARTNAME,
:SALESPRICE :SALESPRICEIND
FROM PURCHDB.PARTS
WHERE PARTNUMBER = :PARTNUMBER;
END-EXEC.
The modified source code is as follows:
**** Start SQL Preprocessor ****
* EXEC SQL
* SELECT PARTNUMBER, PARTNAME, SALESPRICE
* INTO :PARTNUMBER,
* :PARTNAME,
* :SALESPRICE :SALESPRICEIND
* FROM PURCHDB.PARTS
* WHERE PARTNUMBER = :PARTNUMBER
* END-EXEC
**** Start Inserted Statements ****
MOVE PARTNUMBER
TO SQLREC1-FIELD1
MOVE 1 TO SQLSECNUM
MOVE 16 TO SQLINLEN
MOVE 54 TO SQLOUTLEN
CALL "SQLXFETO" USING SQLCA, SQLOWNER, SQLMODNAME,
SQLSECNUM, SQLTEMPV, SQLINLEN, SQLOUTLEN, SQLTRUE
IF SQLCODE IS ZERO
MOVE SQLREC2-FIELD1
TO PARTNUMBER
MOVE SQLREC2-FIELD2
TO PARTNAME
MOVE SQLREC2-FIELD3-IND
TO SALESPRICEIND
IF SQLREC2-FIELD3-IND IS NOT NEGATIVE
MOVE SQLREC2-FIELD3
TO SALESPRICE
END-IF
IF SQLWARN0 IS EQUAL TO "W"
GO TO S500-SQL-WARNING
END-IF
ELSE
IF SQLCODE IS EQUAL TO 100
GO TO S600-NOT-FOUND
END-IF
IF SQLCODE IS NEGATIVE
GO TO S400-SQL-ERROR
END-IF
CONTINUE
END-IF
**** End SQL Preprocessor ****
The embedded SELECT command has been converted into a COBOL comment, and
COBOL statements that enable ALLBASE/SQL to execute the SELECT command at
run time have been inserted. Note that the period following the END-EXEC
now follows the last preprocessor-generated line shown. Note also that
the paragraph named SQLMVS2 is not shown, but appears later in the
modified source code file.
The names that appear in the inserted COBOL code (italicized in the above
example) identify variables used by the ALLBASE/SQL external procedures;
in this example, the names identify variables used by the SQLXFETO
external procedure. Some of these variables are derived from host
variables. As shown in the embedded SELECT command above, you precede a
host variable with a colon when you use it in SQL commands:
:SALESPRICE
Declarations used by preprocessor generated code are defined in the two
copy files which the preprocessor creates:
* SQLCONST, a file that defines variables requiring VALUE clauses
* SQLVAR, a file that defines the remaining variables
The preprocessor inserts $INCLUDE directives that reference these files
in the WORKING-STORAGE SECTION of the modified source code:
$INCLUDE SQLCONST
$INCLUDE SQLVAR
CAUTION Never modify either the statements inserted by the preprocessor
or the include files the preprocessor creates. Changes to
preprocessor-generated information could damage your
DBEnvironment or your system.
Effect of Preprocessing on DBEnvironments
When you invoke the preprocessor, you name an ALLBASE/SQL DBEnvironment.
When preprocessing begins, the preprocessor starts a DBE session for that
DBEnvironment. When preprocessing is completed, the preprocessor
terminates the session.
When the preprocessor encounters a syntactically correct SQL command, it
usually creates an ALLBASE/SQL section and stores it in the system
catalog of the DBEnvironment being accessed. An ALLBASE/SQL section is a
group of stored ALLBASE/SQL instructions for executing one SQL command.
All sections created during a preprocessing session constitute a module.
The preprocessor derives the name of the module from the PROGRAM-ID
unless you supply a different name when you invoke the preprocessor:
:RUN PSQLCOB.PUB.SYS; INFO = 'DBEnvironmentName
(MODULE(ModuleName))'
When the preprocessor terminates the DBEnvironment session, it issues a
COMMIT WORK command if no errors were encountered. Created sections are
stored in the system catalog and associated with the module name.