Indicator
In mainframe programming, particularly COBOL, an indicator is a single-character data item or a special register used to signal a condition, status, or the result of an operation. It acts as a binary flag (on/off, true/false) or a multi-state signal to control program flow or convey information within an application.
Key Characteristics
-
- Data Type: Typically defined as a
PIC X(1)field in COBOL, holding values like 'Y'/'N', '1'/'0', 'T'/'F', or specific single-character codes. - Purpose: Primarily used for conditional logic, loop control, error detection, or to mark specific records or fields for further processing.
- Scope: Can be local to a specific program section, global within a program, or passed between subroutines and modules.
- Special Registers: Some mainframe environments or languages provide built-in indicators, such as COBOL's
RETURN-CODEor CICS'sEIBRESP, which convey system-level status. - Readability: Well-named indicators significantly enhance code readability by explicitly stating the condition or state they represent.
- Data Type: Typically defined as a
Use Cases
-
- COBOL Program Flow Control: Using a
WS-PROCESS-FLAGto determine if a specific processing path should be taken, e.g.,IF WS-PROCESS-FLAG = 'Y' THEN PERFORM PROCESS-ROUTINE. - End-of-File Detection: A common
WS-EOF-INDICATORset to 'Y' when the end of an input file is reached, used to terminate aPERFORM UNTILloop. - Error Handling: Setting an
WS-ERROR-FOUND-SWto '1' within a data validation routine, then checking its value to decide whether to print an error message or abort record processing. - CICS Transaction Status: CICS programs utilize indicators like
EIBRESPor specific flags to check the success or failure of API calls (e.g.,EXEC CICS READ FILE(filename) INTO(record-area) RESP(WS-RESPONSE-CODE)). - DB2 SQL Status: The
SQLCODEandSQLSTATEare effectively indicators returned by DB2 to signal the outcome of an SQL statement, requiring programs to check these values for successful execution or specific error conditions.
- COBOL Program Flow Control: Using a
Related Concepts
Indicators are fundamental to conditional processing and program control flow in COBOL and other mainframe languages. They are closely related to flags, switches, and status codes. For I/O operations, they often work in conjunction with file status codes (e.g., FILE STATUS IS WS-FILE-STATUS) to provide more granular information than a simple end-of-file indicator. In CICS, indicators like EIBRESP are crucial for transaction management and error recovery, while in DB2, SQLCODE and SQLSTATE are essential for database interaction error handling and determining the success or failure of SQL operations.
- Descriptive Naming: Use clear, self-documenting names for indicators, such as
WS-EOF-INDICATOR,WS-VALID-RECORD-FLAG, orWS-PROCESS-COMPLETE-SW, to improve code maintainability. - Consistent Values: Standardize the values used for 'on'/'off' or 'true'/'false' (e.g., always 'Y'/'N' or '1'/'0') across the application or team to enhance consistency.
- Initialize Indicators: Always initialize indicators to their default or starting state before use, especially at the beginning of a program, a loop iteration, or a new record processing cycle.
- Limit Scope: Define indicators with the narrowest possible scope (e.g., within a specific section or paragraph) to avoid unintended side effects and improve modularity, unless they are explicitly designed for global program control.
- Document Usage: Clearly document the purpose, expected values, and the conditions under which indicators are set or checked, especially for those passed between modules or used for critical program logic.