MainframeMaster
MainframeMaster

COBOL Tutorial

Progress0 of 0 lessons

COBOL Message Handling

Message handling in COBOL involves displaying, formatting, and managing messages to users, including error messages, informational messages, warnings, and status updates. Effective message handling provides clear, actionable feedback, improves user experience, aids debugging, and makes programs more maintainable. This includes using DISPLAY statements, formatting messages consistently, managing message codes, handling different message types, and logging messages appropriately.

Basic Message Display

Use DISPLAY statements to output messages:

cobol
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
       PROCEDURE DIVISION.
       DISPLAY-MESSAGES.
           *> Simple text message
           DISPLAY 'Processing started'
           
           *> Message with variable
           DISPLAY 'Customer ID: ' CUSTOMER-ID
           
           *> Error message
           DISPLAY 'ERROR: Invalid customer ID'
           
           *> Formatted message
           DISPLAY 'Transaction ' TRANSACTION-ID ' completed successfully'
           
           STOP RUN.

Message Formatting

Format messages consistently for clarity:

cobol
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
       WORKING-STORAGE SECTION.
       01  MESSAGE-BUFFER           PIC X(100).
       01  ERROR-CODE               PIC X(4) VALUE 'E001'.
       01  ERROR-TEXT               PIC X(50) VALUE 'Invalid input data'.
       
       PROCEDURE DIVISION.
       FORMAT-MESSAGES.
           *> Build formatted error message
           STRING 'ERROR ' DELIMITED BY SIZE
                  ERROR-CODE DELIMITED BY SIZE
                  ': ' DELIMITED BY SIZE
                  ERROR-TEXT DELIMITED BY SIZE
                  INTO MESSAGE-BUFFER
           END-STRING
           
           DISPLAY MESSAGE-BUFFER
           *> Output: ERROR E001: Invalid input data
           
           STOP RUN.

Message Code System

Use message codes for maintainability:

cobol
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
       WORKING-STORAGE SECTION.
       01  MESSAGE-TABLE.
           05  MESSAGE-ENTRY OCCURS 10 TIMES
                            INDEXED BY MSG-INDEX.
               10  MSG-CODE          PIC X(4).
               10  MSG-TEXT          PIC X(50).
       
       01  MESSAGE-BUFFER           PIC X(100).
       
       PROCEDURE DIVISION.
       INITIALIZE-MESSAGES.
           *> Initialize message table
           MOVE 'E001' TO MSG-CODE(1)
           MOVE 'Invalid customer ID' TO MSG-TEXT(1)
           
           MOVE 'E002' TO MSG-CODE(2)
           MOVE 'File not found' TO MSG-TEXT(2)
           
           MOVE 'W001' TO MSG-CODE(3)
           MOVE 'Low balance warning' TO MSG-TEXT(3)
       
       DISPLAY-MESSAGE-BY-CODE.
           *> Look up and display message by code
           PERFORM VARYING MSG-INDEX FROM 1 BY 1
                   UNTIL MSG-INDEX > 10
               IF MSG-CODE(MSG-INDEX) = 'E001'
                   STRING 'ERROR ' DELIMITED BY SIZE
                          MSG-CODE(MSG-INDEX) DELIMITED BY SIZE
                          ': ' DELIMITED BY SIZE
                          MSG-TEXT(MSG-INDEX) DELIMITED BY SIZE
                          INTO MESSAGE-BUFFER
                   END-STRING
                   DISPLAY MESSAGE-BUFFER
                   EXIT PERFORM
               END-IF
           END-PERFORM
           
           STOP RUN.

Message Types

Handle different message types appropriately:

cobol
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
       WORKING-STORAGE SECTION.
       01  MESSAGE-TYPE             PIC X.
           88  ERROR-MESSAGE        VALUE 'E'.
           88  WARNING-MESSAGE      VALUE 'W'.
           88  INFO-MESSAGE         VALUE 'I'.
       
       PROCEDURE DIVISION.
       DISPLAY-BY-TYPE.
           IF ERROR-MESSAGE
               STRING 'ERROR: ' DELIMITED BY SIZE
                      MESSAGE-TEXT DELIMITED BY SIZE
                      INTO MESSAGE-BUFFER
               END-STRING
               DISPLAY MESSAGE-BUFFER
               *> Errors may stop processing
           ELSE
               IF WARNING-MESSAGE
                   STRING 'WARNING: ' DELIMITED BY SIZE
                          MESSAGE-TEXT DELIMITED BY SIZE
                          INTO MESSAGE-BUFFER
                   END-STRING
                   DISPLAY MESSAGE-BUFFER
                   *> Warnings continue with caution
               ELSE
                   IF INFO-MESSAGE
                       STRING 'INFO: ' DELIMITED BY SIZE
                              MESSAGE-TEXT DELIMITED BY SIZE
                              INTO MESSAGE-BUFFER
                       END-STRING
                       DISPLAY MESSAGE-BUFFER
                       *> Info messages provide status
                   END-IF
               END-IF
           END-IF
           
           STOP RUN.

Error Message Best Practices

Effective error messages should:

  • Be clear and concise: Easy to understand
  • Include context: What operation failed, what data was involved
  • Provide guidance: What the user should do
  • Use consistent format: Same structure for all errors
  • Include relevant data: Show values that caused the error

Logging Messages

Log important messages to files:

cobol
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
       FILE SECTION.
       FD  LOG-FILE
           LABEL RECORDS ARE STANDARD.
       01  LOG-RECORD               PIC X(200).
       
       WORKING-STORAGE SECTION.
       01  CURRENT-DATE-TIME        PIC X(21).
       01  LOG-MESSAGE              PIC X(150).
       
       PROCEDURE DIVISION.
       LOG-MESSAGE.
           *> Get timestamp
           MOVE FUNCTION CURRENT-DATE TO CURRENT-DATE-TIME
           
           *> Build log entry
           STRING CURRENT-DATE-TIME(1:14) DELIMITED BY SIZE
                  ' | ERROR E001 | ' DELIMITED BY SIZE
                  'Invalid customer ID: ' DELIMITED BY SIZE
                  CUSTOMER-ID DELIMITED BY SIZE
                  INTO LOG-MESSAGE
           END-STRING
           
           *> Write to log file
           MOVE LOG-MESSAGE TO LOG-RECORD
           WRITE LOG-RECORD
           
           STOP RUN.

Test Your Knowledge

1. What is the primary way to display messages in COBOL?

  • PRINT statement
  • DISPLAY statement
  • MESSAGE statement
  • OUTPUT statement

2. What should error messages include?

  • Just the error code
  • Error code, description, context, and guidance
  • Only the error description
  • Just context information

3. What is a message code system?

  • A way to encode messages
  • A system that assigns unique codes to messages for management
  • A way to compress messages
  • A way to encrypt messages

4. How do you build formatted messages?

  • Using FORMAT statement
  • Using STRING to combine message parts
  • Messages cannot be formatted
  • Using MOVE only

5. Why use message codes instead of hardcoded text?

  • To make code shorter
  • For easier maintenance, translation, and consistency
  • To improve performance
  • To reduce memory usage

Related Concepts

Related Concepts

DISPLAY Statement

Learn about displaying output

STRING Statement

Understanding string building for messages

Error Handling

Understanding error handling techniques

File Operations

Writing messages to log files

Related Pages