Initialize
Enhanced Definition
Key Characteristics
-
- State Reset: Involves clearing previous contents, setting default values (e.g., zeros, spaces), or formatting a structure to a baseline state.
- Pre-usage Requirement: Typically performed before a resource can be read from, written to, or otherwise actively used by a program or the operating system.
- Scope: Can apply at various levels, from individual program variables within an application to entire disk volumes or system components during an
IPL(Initial Program Load). - Prevention of Undefined Behavior: Crucial for preventing programs from operating on "garbage" data (unpredictable values left over from previous operations), which can lead to errors, abends, or security vulnerabilities.
- Language and Utility Support: Modern programming languages (like COBOL) provide explicit
INITIALIZEstatements, while system utilities (likeICKDSForIDCAMS) handle dataset and device initialization.
Use Cases
-
- Program Variable Initialization: Setting COBOL
PIC Xfields toSPACESorPIC 9fields toZEROSat the start of a program or subroutine using theINITIALIZEverb to ensure a clean slate for calculations or data manipulation. - New Dataset Creation: Formatting a newly allocated
VSAMKSDS or ESDS dataset usingIDCAMS DEFINE CLUSTERwithREUSEorERASEoptions, or a sequential dataset, to prepare it for data storage. - Disk Volume Initialization: Using the
ICKDSFutility to format a new DASD (Direct Access Storage Device) volume, writing track zeros, and creating the Volume Table of Contents (VTOC) before it can be used by z/OS. - Control Block Setup: Operating system routines or application programs initializing control blocks (e.g., Task Control Blocks, Data Control Blocks) with default values and pointers before they are used to manage system resources or I/O operations.
- Program Variable Initialization: Setting COBOL
Related Concepts
Initialization is fundamental to the ALLOCATE and OPEN processes; a resource is often allocated and then implicitly or explicitly initialized before it can be opened for I/O. It is a critical step in IPL (Initial Program Load), where the entire z/OS system and its components are initialized to a known operational state. The COBOL INITIALIZE statement provides a high-level language mechanism for this, while JCL DD statements often trigger underlying system initialization for datasets and devices.
Best Practices:
- Explicit Initialization: Always explicitly initialize program variables, especially working storage fields, to avoid relying on default or undefined values that can lead to subtle bugs and unpredictable program behavior.
- Use System Utilities: Leverage z/OS system utilities (e.g.,
IDCAMS,ICKDSF,IEBGENERfor dataset clearing) for robust and correct initialization of datasets and storage devices. - Understand Language Defaults: Be aware of how different programming languages (COBOL, PL/I, Assembler) handle default initialization for various data types and structures, and override defaults where necessary for clarity and safety.
- Security Considerations: For sensitive data, ensure