Cobol Coding Standards

1.         COBOL STANDARDS

The following standards can be followed while coding COBOL programs.  

1.1     General

·         Comments should be used at the start of the procedure division to give a general overview of the program and should also be used throughout the program to explain the reasons for processing.

·         Use of limited blank lines must be made throughout the program to improve readability.

·         All Warnings issued during compilation of the COBOL program must be investigated and eliminated, if possible.

·         Changes to existing programs/common modules are written in the same style as the original code.

1.2    Identification Division. 

·         This must consist of at least the following entries:

          PROGRAM-ID  

          AUTHOR     

          INSTALLATION

          DATE-WRITTEN

          DATE-COMPILED

·         The PROGRAM-ID should be same as the program name.

·         At the end of the Division there must be a summary description of the program and its modification history.   

·         For new programs give just heading lines for modification history.

·         Give the details of input and output files, copybooks being used in the program.

1.3     Environment Division.

·         File Status must be used for all files.

·         Select statements in the File-Control are in the same order as the corresponding FDs in the File Section of the Data Division.

·         Each clause on the SELECT statement should start on a separate line.

·         File names can have prefix  ‘I’ for input files and ‘O’ for output files. The order of select statements for the files can be input files, then updated files and then output files.

Ex.     SELECT I-FILE  ASSIGN TO DD1

          SELECT O-FILE ASSIGN TO DD2

1.4     Data Division

·         FD must be preceded by a blank line with ‘*’ in column 7.

·         Proper and meaningful names must be used for data names.

·         Level numbers within the division must begin with '01' in column 8 and indented 4 columns to the right for each increase in number. The subsequent levels must be '05', '10' etc.

·         Clauses must all be column-aligned and begin after column 34 using a separate line from the field name if necessary.

·         PIC clause must be in column 40.If the field name goes beyond 38, PIC must start from column 40 of the next line.

·         It is recommended that signed packed decimal (COMP-3) fields are used for numeric items that are used in arithmetic operations. It is also recommended that COMP fields are used for indexing.

1.4.1 File Section

·         FD entries must occur in the same order as their corresponding SELECT statement in the Environment Division.

·         Copybooks should be used for file layouts (If applicable).

·         Record layouts must follow a standard convention that will enable a particular record or element to be easily cross-referenced.

1.4.2 Working-Storage Section 

·         The Working Storage must be preceded by  an ’eye-catcher’ of the format:

              77  FILLER                      PIC X(32) VALUE

                                   'START PNB0412B WORKING STORAGE'.

·         The following code must be used in the program 

     01 PGM-INFO.                                                 

          03  FILLER                     PIC X(09) VALUE 'PROGRAM:'.          

          03  PGM-ID                     PIC X(08) VALUE 'program name'.          

          03  FILLER                               PIC X(10) VALUE '  VERSION:'.        

          03  PGM-VERSION        PIC X(02) VALUE '01'.                

          03  FILLER                               PIC X(30) VALUE   '  LAST COMPILE TIME AND DATE:'.

          03  PGM-COMPILED     PIC X(8).                            

         

     And in Procedure Division have the following statements executed first

                     MOVE WHEN-COMPILED TO PGM-COMPILED OF PGM-INFO

                     DISPLAY PGM-INFO

·         Data names within Working-Storage must be prefixed by WS.

·           Like data items must be defined together and given the same prefix. And in grouping, the fields should be declared in alphabetical order as far as possible.

       e.g. all Dates, Counters , Constants , Flags, Index, PARMs and all print fields etc.

·         Each group must be preceded by a comment.

·         If a data element in Working-storage corresponds to a data element in the File Section then the only difference in their names must be the prefix.

·         All constants/pre-set literals must be defined with the value clause (e.g. messages, headings etc).

·         If a variable whose value changes during program execution needs an initial value, move the value in the INITIALIZE paragraph in Procedure Division rather than using a value clause in the working storage section.

·         Processing will be made easier to follow if counters, totals, subscripts etc are initialized before use.

·         88 Levels should be used to clarify procedure code. They must be indented from their corresponding variable and must have the same prefix.

·         Database variables (ALL INCLUDE statements)  must be declared at the end of the working storage section each  preceded by a  comment containing a brief description.

·         The working storage section must be ended with an eye-catcher of the format

                         01  FILLER                                        PIC X(40)

                                                           VALUE 'END <program name> WORKING STORAGE'.

1.4.3 Linkage Section

·         The data name must be the same as the corresponding data name in the calling module.

1.5     Procedure Division 

The following are the general standards to be observed when coding the Procedure Division:

·         The first section of the program must be named similar to 0000-MAIN-PARA .

·         The format of the 0000-MAIN-PARA section should be as follows:-

             PERFORM 1000-INIT-PARA                      THRU 1000-EXIT.

             PERFORM 2000-PROCESS-PARA            THRU 2000-EXIT.

             PERFORM 9000-TERMINATE-PARA        THRU 9000-EXIT .

             STOP RUN.

·         OPEN/CLOSE one file at a time. Always check for the file status after each file is accessed.

·         Always Check SQLCODE after executing an SQL statement.

·         There should be a standard ERROR paragraph, which will take care of all error processing. As soon as an error is detected (for e.g., OPEN failure, READ failure, WRITE failure etc) appropriate error variables must be set and control transferred to the ERROR paragraph.

·         This ERROR paragraph will pass the necessary information to the Error-handling routine which will generate the error report, set a return-code or abend the program depending on severity of error .

·         Blank lines must be used to break up the code and improve readability. For example, before and after the outermost IF statements, PERFORM statements etc.

·         IF statements must check for the most likely occurrence first, where possible.

·         All IF statements should be clearly understandable (indented, no double negatives).

      Code ELSE statement alone on a separate line.

·         All EVALUATE statements should contain ‘WHEN OTHER’.

·         Explicit terminators must be used for IF statements (i.e.) END-IF must be used. In-line PERFORMS must be terminated with the corresponding END-PERFORM statement. If EVALUATE statements are used, they must have a corresponding END-EVALUATE

·         Preferably, all ‘TO’ in MOVE and SET statements must be at column 40. If this is not possible, within a paragraph the TO clause must be aligned.

·          Periods must not be used unless necessary. Only one period just before the end of each paragraph must be coded. Periods must be on separate line and nothing else must be on the line.

·         Avoid using GO TO. A forward GOTO to the corresponding EXIT paragraph can be used. Also it can be used when its use will significantly simplify the coding.

·         Program has only one exit point -  'GO BACK’ or ‘STOP RUN’.

·         All CALLs must be dynamic. This means the name of the program to be called must be held in working storage fields and the program called using this variable. For example,

         WC-ERROR-PROGRAM                    PIC X(6)          VALUE 'PGM001'.

         CALL WC-ERROR-PROGRAM USING WL-ERROR-VARIABLE

·          Use comments before CALL of any sub-program, sub-routine.

·         For arithmetic operations the following considerations apply

- No Display fields to be used as far as possible. 

- All fields have the same decimal alignment

·         Comparison must be done for fields satisfying the criteria

- Both fields have the same usage.

      - Alphanumeric fields are of equal length.

      - Numeric fields have the same decimal alignment.

      - Signed display fields must not be compared with alphanumeric fields

·         When 'MOVE'ing fields ensure as far as possible that :

 -  Both fields must have the same usage

-  In an alphanumeric MOVE, the receiving field length should equal the sending field length if possible, or else the receiving fields should be longer.

       -  There should be no truncation on a MOVE.

    -  COMP fields should be word aligned

       -  Numeric fields should have the same decimal alignment

       -  Conversion must be kept to a minimum

·         COMPUTE verb should be used in place of DIVIDE and MULTIPLY. For addition and subtraction, ADD, SUBTRACT may be used instead of COMPUTE verb.

·         Check for ZERO divisor before DIVISION.

·         The Use of Corresponding clauses should be avoided.

·         SET - Use SET < condition name > to TRUE rather than move specific values to variables.

·         SEARCH - Use Serial SEARCH when < 20 elements, else use binary search.

·         GO TO DEPENDING ON should not be used. Use EVALUATE instead

·         EXIT PROGRAM - not to be used. Instead GOBACK should be used

·         Use the CONTINUE statement and not the NEXT SENTENCE statement.

·         Do not use   ACCEPT to obtain data from a SYSIN DD * card

·         Avoid deliberate use of PERFORM for few statements. The number of instructions required to execute PERFORM may be more than that required to execute those statements.

  

 Error Handling:

Unexpected errors must be catered for within the program in a consistent manner. The use of Displays must be avoided as far as possible.

General coding principles:

The ALTER instruction must not be used as it makes the code unnecessarily complex.

It is recommended that index rather than subscripts are used when accessing tables.

It is recommended that the 'SET condition-name TO TRUE' statement be used for assigning values to condition names when using 88 level indicators.

Structure:

Full use should be made of the verbs and constructs available with COBOL II i.e. INITIALIZE, END-IF, END-PERFORM, EVALUATE. Only use INITIALIZE to set groups to zero or spaces and restrict its use to the INIT section if possible. Do not use it to set fields to other values as this is very inefficient.

Maintainability:

Code should be easy to understand and therefore easy to maintain. Complex logic that will save a small amount of coding should be avoided if it is difficult to follow.

Batch Output Files:

Programs writing output files should be opened with OUTPUT not EXTEND. The JCL displacement should reflect a file extension with DISP=MOD and DISP=OLD for files being overwritten.

User Controlled Abends:

Under certain conditions it may be required to terminate a program in a controlled manner. An Example of this could be when the integrity of a data file cannot be determined.

For DB2 programs the "User Abend" is the safest way to terminate a program to force a rollback of any work up to the last commit point.

The user abend is invoked by using code similar to the following:-

                           COPY ABEND. (In Working-storage section)

          Code

                           MOVE '1234' TO WS-ABEND-CODE.

                           CALL ' ZZZABEND' USING WS-ABEND-CODE.

The above code will cause the program to abend with a completion code of "U1234".

Note: Only values in the range 0-4095 can be used s user abend codes due to the picture clause used by module ZZZABEND.

An alternative method in DB2 programs is to issue a ROLLBACK, terminate the program with the RETURN-CODE set.  This will ensure any output files are retained.

To terminate a program without an ABEND (ie. there are no database updates to consider) a simpler method can be used. COBOL contains a reserved dataname called RETURN-CODE. A value can be moved to this dataname during any point within a program and the return code will be set on completion.

             eg.        MOVE 8 to RETURN-CODE.

         

Sub-programs should not issue abends or set the return code, instead they should pass status codes back to the calling program where action will be taken.