The BASED clause in COBOL provides sophisticated pointer-based data structure capabilities that enable dynamic memory allocation, flexible data access patterns, and advanced memory management techniques. This powerful feature allows COBOL programs to work with data structures whose size and location are determined at runtime, making it possible to implement complex algorithms, handle variable-length data efficiently, and create dynamic data structures such as linked lists, trees, and hash tables. Understanding the BASED clause is essential for developing high-performance COBOL applications that require optimal memory usage, dynamic data management, or integration with other programming languages that use pointer-based architectures.
BASED data items represent a significant advancement in COBOL's data handling capabilities, bridging the gap between traditional fixed-structure COBOL programming and modern dynamic memory management techniques. This functionality is particularly valuable in enterprise applications that must process varying data sizes, implement efficient algorithms, or interface with systems that require dynamic memory allocation.
BASED data items are special data structures that don't have a fixed memory location when defined. Instead, they are associated with pointer variables that determine where the data item is located in memory at runtime. This approach provides tremendous flexibility for handling dynamic data structures, implementing memory-efficient algorithms, and creating applications that can adapt to varying data requirements without predefined size limitations.
The BASED clause fundamentally changes how COBOL handles memory allocation and data access. Unlike traditional COBOL data items that have fixed memory locations determined at compile time, BASED items can be repositioned in memory, duplicated, or deallocated as needed during program execution. This capability enables implementation of sophisticated data structures and algorithms that would be difficult or impossible with traditional COBOL data declaration methods.
12345678910111213141516171819202122232425262728DATA DIVISION. WORKING-STORAGE SECTION. *> Pointer variable declaration 01 WS-CUSTOMER-POINTER USAGE POINTER. 01 WS-NODE-POINTER USAGE POINTER. *> BASED data item declaration 01 CUSTOMER-RECORD BASED(WS-CUSTOMER-POINTER). 05 CUSTOMER-ID PIC 9(8). 05 CUSTOMER-NAME PIC X(50). 05 CUSTOMER-ADDRESS PIC X(100). 05 NEXT-CUSTOMER-PTR USAGE POINTER. 01 LIST-NODE BASED(WS-NODE-POINTER). 05 NODE-DATA PIC X(256). 05 NEXT-NODE-PTR USAGE POINTER. PROCEDURE DIVISION. ALLOCATE-MEMORY-EXAMPLE. *> Allocate memory for BASED item ALLOCATE CUSTOMER-RECORD. *> Set the pointer to point to allocated memory SET WS-CUSTOMER-POINTER TO ADDRESS OF CUSTOMER-RECORD. *> Access the BASED data item through the pointer MOVE 12345678 TO CUSTOMER-ID. MOVE "John Smith Industries Inc." TO CUSTOMER-NAME.
1234567891011121314151617181920212223242526272829303132333435*> Dynamic linked list implementation using BASED DATA DIVISION. WORKING-STORAGE SECTION. 01 WS-HEAD-POINTER USAGE POINTER VALUE NULL. 01 WS-CURRENT-POINTER USAGE POINTER. 01 WS-NEW-POINTER USAGE POINTER. 01 LINKED-LIST-NODE BASED(WS-CURRENT-POINTER). 05 NODE-ID PIC 9(8). 05 NODE-DATA PIC X(100). 05 NEXT-NODE-PTR USAGE POINTER. PROCEDURE DIVISION. CREATE-LINKED-LIST. PERFORM VARYING WS-COUNTER FROM 1 BY 1 UNTIL WS-COUNTER > 10 PERFORM ADD-LIST-NODE END-PERFORM. ADD-LIST-NODE. *> Allocate new node ALLOCATE LINKED-LIST-NODE SET WS-NEW-POINTER TO ADDRESS OF LINKED-LIST-NODE *> Set current pointer to new node SET WS-CURRENT-POINTER TO WS-NEW-POINTER *> Initialize node data MOVE WS-COUNTER TO NODE-ID STRING "Node data for item " WS-COUNTER INTO NODE-DATA *> Link to previous head SET NEXT-NODE-PTR TO WS-HEAD-POINTER *> Update head pointer SET WS-HEAD-POINTER TO WS-NEW-POINTER.
Use BASED data items when you need dynamic memory allocation, variable-sized data structures, or when implementing complex algorithms like linked lists, trees, or graphs. They're also valuable when interfacing with other systems or when memory efficiency is critical.
Always pair ALLOCATE statements with corresponding FREE statements. Implement proper error handling and cleanup routines. Consider using working storage to track allocated pointers and ensure all allocated memory is freed before program termination.
Create a program that implements a dynamic array using BASED data items. The array should be able to grow and shrink as needed, with functions to add, remove, and access elements.