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COBOL DEBUG-SUB-3 Clause - Quick Reference

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Overview

The DEBUG-SUB-3 clause is used to define debugging data items that track the third subscript value being used in three-dimensional array or table operations during program debugging. This clause is part of COBOL's debugging facility and provides essential third subscript tracking for cube debugging and analysis.

Purpose and Usage

  • Third subscript tracking - Track third subscript in 3D array operations
  • Cube access monitoring - Monitor cube element access
  • Depth bounds checking - Identify cube depth bounds issues
  • Cube pattern analysis - Analyze cube access patterns
  • Development support - Aid in cube debugging

Third Subscript Tracking Concept

Cube Access: CUBE[1,1,1] → CUBE[1,1,2] → CUBE[1,2,1] → ...
DEBUG-SUB-1: [Row Index]
DEBUG-SUB-2: [Column Index]
DEBUG-SUB-3: [Depth Index]
Tracks third subscript (depth) value in 3D array operations

DEBUG-SUB-3 provides real-time tracking of the third subscript value in three-dimensional array operations.

Syntax

The DEBUG-SUB-3 clause follows specific syntax patterns and is typically used at the 77 level for independent debugging data items.

Basic Syntax

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* Basic DEBUG-SUB-3 clause syntax
77 debug-sub-3-item DEBUG-SUB-3.
 
* Examples
77 DEBUG-THIRD-SUB DEBUG-SUB-3.
77 DEBUG-SUB-3-VALUE DEBUG-SUB-3.
77 DEBUG-CUBE-SUB-3 DEBUG-SUB-3.
 
* Complete example with data description
77 DEBUG-THIRD-SUB DEBUG-SUB-3 PIC 9(5).
77 DEBUG-SUB-3-VALUE DEBUG-SUB-3 PIC 9(6).
77 DEBUG-CUBE-SUB-3 DEBUG-SUB-3 COMP.
 
* Usage in program
PROCEDURE DIVISION.
    * Display current third subscript value
    DISPLAY "Third subscript: " DEBUG-THIRD-SUB
    
    * Store subscript for later use
    MOVE DEBUG-THIRD-SUB TO SAVED-SUBSCRIPT-3
    
    * Check if at specific subscript
    IF DEBUG-THIRD-SUB = 100
        DISPLAY "Accessing depth 100"
    END-IF

DEBUG-SUB-3 is typically used at the 77 level for independent debugging items.

Data Type Considerations

Data TypeSizeUse Case
PIC 9(5)5 digitsCubes up to 99,999 layers
PIC 9(6)6 digitsLarge cubes up to 999,999 layers
COMPBinaryEfficient storage and processing
COMP-3Packed decimalMainframe compatibility

Debugging Mode Requirements

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* Enabling debugging mode for DEBUG-SUB-3
* Compiler option
* Example: cobc -fdebug program.cob
 
* Runtime debugging activation
* Set environment variable
* Example: COBOL_DEBUG=1 ./program
 
* Program-level debugging declaration
PROGRAM-ID. DEBUG-PROGRAM.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SPECIAL-NAMES.
    DEBUGGING MODE IS ON.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
77 DEBUG-THIRD-SUB DEBUG-SUB-3 PIC 9(5).

DEBUG-SUB-3 requires debugging mode to be enabled for third subscript tracking functionality.

Common Use Cases

DEBUG-SUB-3 is commonly used in specific debugging scenarios where third subscript tracking is needed for three-dimensional array analysis.

Cube Access Tracking

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* Tracking cube access patterns
77 DEBUG-THIRD-SUB DEBUG-SUB-3 PIC 9(5).
 
PROCEDURE DIVISION.
    DISPLAY "Starting cube access at depth: " DEBUG-THIRD-SUB
    
    * Process cube elements
    PERFORM VARYING I FROM 1 BY 1 UNTIL I > 10
        PERFORM VARYING J FROM 1 BY 1 UNTIL J > 10
            PERFORM VARYING K FROM 1 BY 1 UNTIL K > 10
                * Access cube element
                MOVE CUBE(I, J, K) TO TEMP-VALUE
                DISPLAY "Accessing element at depth: " DEBUG-THIRD-SUB
            END-PERFORM
        END-PERFORM
    END-PERFORM
    
    DISPLAY "Cube processing completed at depth: " DEBUG-THIRD-SUB

Track which cube depths are being accessed.

Cube Bounds Monitoring

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* Monitoring cube bounds
77 DEBUG-THIRD-SUB DEBUG-SUB-3 PIC 9(5).
77 CUBE-DEPTH PIC 9(5) VALUE 100.
 
PROCEDURE DIVISION.
    * Check for depth bounds violations
    IF DEBUG-THIRD-SUB > CUBE-DEPTH
        DISPLAY "WARNING: Cube depth bounds violation at: " DEBUG-THIRD-SUB
        DISPLAY "Cube depth is: " CUBE-DEPTH
    END-IF
    
    * Monitor specific depth ranges
    IF DEBUG-THIRD-SUB >= 90 AND DEBUG-THIRD-SUB <= 100
        DISPLAY "Accessing high-index depths at: " DEBUG-THIRD-SUB
        * Add extra validation here
    END-IF
    
    * Track zero-based access
    IF DEBUG-THIRD-SUB = 0
        DISPLAY "WARNING: Zero-based cube access detected"
    END-IF

Monitor cube depth bounds and identify potential violations.

Conditional Cube Debugging

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* Conditional debugging based on third subscripts
77 DEBUG-THIRD-SUB DEBUG-SUB-3 PIC 9(5).
 
PROCEDURE DIVISION.
    * Only show debugging info for specific depth ranges
    IF DEBUG-THIRD-SUB >= 1 AND DEBUG-THIRD-SUB <= 10
        DISPLAY "Debug info for low depths: " DEBUG-THIRD-SUB
        DISPLAY "Cube value = " CUBE(DEBUG-SUB-1, DEBUG-SUB-2, DEBUG-THIRD-SUB)
    END-IF
    
    * Break execution at specific depth
    IF DEBUG-THIRD-SUB = 50
        DISPLAY "Breakpoint reached at depth 50"
        * Add breakpoint logic here
    END-IF
    
    * Track access frequency
    IF DEBUG-THIRD-SUB = 25
        ADD 1 TO DEPTH-ACCESS-COUNT
        DISPLAY "Depth 25 accessed " DEPTH-ACCESS-COUNT " times"
    END-IF

Use third subscripts to implement conditional debugging logic.

Best Practices and Tips

Following these best practices ensures effective use of the DEBUG-SUB-3 clause for cube debugging and third subscript tracking.

DEBUG-SUB-3 Design Principles

  • Choose appropriate size - Select data type that accommodates your largest cube
  • Use meaningful names - Choose descriptive names for debugging subscript items
  • Minimize overhead - Don\'t overuse subscript tracking to avoid performance impact
  • Document cube dimensions - Document expected cube bounds for validation
  • Consider production impact - Remember that subscript tracking can affect performance
  • Test debugging functionality - Verify that subscript tracking works correctly

Common Pitfalls to Avoid

PitfallProblemSolution
Insufficient field sizeSubscript values overflowChoose appropriate PIC size for largest cube
Overuse in productionPerformance degradationUse conditional compilation or separate versions
Not enabling debug modeNo subscript tracking informationEnsure debugging mode is properly enabled
Poor naming conventionsConfusing debugging outputUse clear, descriptive names
Not documenting usageDifficult to understand subscript trackingDocument all subscript tracking items and their purpose

Performance Considerations

  • Subscript tracking overhead - DEBUG-SUB-3 adds runtime overhead when active
  • Memory usage - Subscript tracking items consume additional memory
  • I/O impact - Subscript tracking output may affect I/O performance
  • Production considerations - Disable subscript tracking in production environments
  • Selective tracking - Use conditional logic for selective subscript tracking
  • Debugging levels - Consider different levels of subscript tracking detail

When to Use DEBUG-SUB-3

Use CaseDEBUG-SUB-3 SuitabilityReasoning
Cube debuggingExcellentEssential for cube third subscript tracking
Complex cube operationsGoodHelps track complex cube access patterns
Depth bounds checkingGoodProvides cube depth bounds validation
Production monitoringPoorPerformance impact outweighs benefits
Simple programsPoorUnnecessary overhead for simple logic

DEBUG-SUB-3 Clause Quick Reference

UsageSyntaxExample
Basic third subscript tracking77 debug-sub-3-item DEBUG-SUB-377 DEBUG-SUB-3 DEBUG-SUB-3
With data description77 debug-sub-3-item DEBUG-SUB-3 PIC...77 DEBUG-SUB-3 DEBUG-SUB-3 PIC 9(5)
Multiple subscript trackersMultiple 77 items with DEBUG-SUB-377 DEBUG1 DEBUG-SUB-3
77 DEBUG2 DEBUG-SUB-3
Numeric subscript tracking77 debug-sub-3-item DEBUG-SUB-3 PIC 9(n)77 DEBUG-SUB-3 DEBUG-SUB-3 PIC 9(6)
Binary subscript tracking77 debug-sub-3-item DEBUG-SUB-3 COMP77 DEBUG-SUB-3 DEBUG-SUB-3 COMP

Test Your Knowledge

1. What is the primary purpose of the DEBUG-SUB-3 clause in COBOL?

  • To define data types
  • To track the third subscript value during debugging
  • To control file operations
  • To perform calculations

2. At what level is the DEBUG-SUB-3 clause typically used?

  • 01 level only
  • 88 level only
  • 77 level only
  • Any level except 01

3. What information does DEBUG-SUB-3 provide during debugging?

  • Only variable names
  • Only program flow
  • Third subscript value in three-dimensional array operations
  • Only error messages

4. When is DEBUG-SUB-3 most useful?

  • During production runs
  • During program development and debugging with three-dimensional arrays
  • Only during compilation
  • Only during program termination

5. How does DEBUG-SUB-3 relate to three-dimensional array debugging?

  • They are completely independent
  • DEBUG-SUB-3 provides essential third subscript tracking for 3D arrays
  • DEBUG-SUB-3 overrides other debugging features
  • They serve the same purpose

Frequently Asked Questions

Related Concepts

DEBUG-SUB-1 Clause

Understanding the DEBUG-SUB-1 clause for first subscript tracking.

DEBUG-SUB-2 Clause

Understanding the DEBUG-SUB-2 clause for second subscript tracking.

OCCURS Clause

Understanding array definitions and OCCURS clause.

Table Handling

Complete guide to table and array operations.

Data Types

Understanding COBOL data types for arrays.

DEBUG-SUB-2 ClauseDEBUG-CONTENTS Clause