COBOL Tutorial

COBOL ALLOCATE Statement

The ALLOCATE statement represents one of COBOL's most sophisticated and essential dynamic memory management mechanisms, serving as the fundamental tool for runtime storage allocation, dynamic data structure creation, and advanced memory management in modern business applications. Far more than a simple memory allocation directive, the ALLOCATE statement embodies COBOL's comprehensive approach to dynamic storage management by providing precise control over memory allocation patterns, runtime storage optimization, variable-length data handling, and complex memory management strategies that enable applications to efficiently handle dynamic data requirements while maintaining the safety and performance characteristics that make COBOL ideal for enterprise computing environments requiring sophisticated memory management capabilities.

In enterprise computing environments, the ALLOCATE statement serves as a critical foundation for advanced data architecture, enabling developers to create sophisticated business applications that handle variable data structures, dynamic processing requirements, memory-efficient algorithms, and scalable data management patterns. Its capabilities extend far beyond simple memory allocation to encompass sophisticated storage optimization, dynamic data structure management, memory pool coordination, and integration with modern memory management systems that are essential for applications requiring optimal memory utilization and dynamic storage management capabilities.

ALLOCATE Statement Syntax and Usage

Basic ALLOCATE Syntax

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*> Basic ALLOCATE statement
ALLOCATE BASED-RECORD.
 
*> ALLOCATE with INITIALIZED
ALLOCATE BASED-RECORD INITIALIZED.
 
*> ALLOCATE with RETURNING pointer
ALLOCATE BASED-RECORD RETURNING WS-POINTER.
 
*> ALLOCATE with both options
ALLOCATE BASED-RECORD INITIALIZED RETURNING WS-POINTER.

Basic ALLOCATE syntax for dynamic memory allocation with optional initialization and pointer return.

ALLOCATE with BASED Variables

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*> Define BASED variable
01  DYNAMIC-RECORD BASED.
    05  RECORD-ID        PIC X(10).
    05  RECORD-DATA      PIC X(100).
    05  RECORD-COUNT     PIC 9(5).
 
*> Allocate memory for BASED variable
ALLOCATE DYNAMIC-RECORD.
 
*> Use the allocated memory
SET ADDRESS OF DYNAMIC-RECORD TO WS-POINTER.
MOVE "REC001" TO RECORD-ID.
MOVE "Sample data" TO RECORD-DATA.
MOVE 1 TO RECORD-COUNT.
 
*> Free the memory when done
FREE DYNAMIC-RECORD.

ALLOCATE with BASED variables enables dynamic data structure creation and manipulation.

ALLOCATE with Variable Lengths

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*> Variable-length BASED structure
01  VARIABLE-RECORD BASED.
    05  HEADER-INFO.
        10  RECORD-TYPE   PIC X(5).
        10  DATA-LENGTH   PIC 9(5).
    05  VARIABLE-DATA.
        10  DATA-ITEMS OCCURS 1 TO 1000 TIMES
                       DEPENDING ON DATA-LENGTH
                       PIC X(20).
 
*> Allocate with calculated size
COMPUTE WS-ALLOCATION-SIZE = 
    LENGTH OF HEADER-INFO + (WS-ITEM-COUNT * 20).
ALLOCATE WS-ALLOCATION-SIZE CHARACTERS RETURNING WS-POINTER.
SET ADDRESS OF VARIABLE-RECORD TO WS-POINTER.

ALLOCATE supports variable-length structures with runtime size calculation.

Comprehensive Example

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IDENTIFICATION DIVISION.
PROGRAM-ID. ALLOCATE-DEMO.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
 
*> BASED variable definitions
01  CUSTOMER-RECORD BASED.
    05  CUST-ID           PIC X(10).
    05  CUST-NAME         PIC X(30).
    05  CUST-BALANCE      PIC S9(8)V99.
    05  CUST-STATUS       PIC X(10).
 
01  TRANSACTION-RECORD BASED.
    05  TRANS-HEADER.
        10  TRANS-COUNT   PIC 9(5).
        10  TRANS-TOTAL   PIC S9(10)V99.
    05  TRANS-DETAILS.
        10  TRANS-ITEMS OCCURS 1 TO 1000 TIMES
                        DEPENDING ON TRANS-COUNT.
            15  TRANS-ID    PIC X(12).
            15  TRANS-AMOUNT PIC S9(8)V99.
 
01  DYNAMIC-BUFFER BASED.
    05  BUFFER-SIZE       PIC 9(8) BINARY.
    05  BUFFER-DATA       PIC X(32000).
 
*> Pointer variables
01  CUSTOMER-POINTER     POINTER.
01  TRANSACTION-POINTER  POINTER.
01  BUFFER-POINTER       POINTER.
 
*> Control variables
01  WS-ALLOCATION-SIZE   PIC 9(8) BINARY.
01  WS-ITEM-COUNT        PIC 9(5).
01  WS-COUNTER           PIC 9(5).
01  WS-TOTAL-ALLOCATED   PIC 9(10) VALUE 0.
01  WS-ALLOCATION-COUNT  PIC 9(5) VALUE 0.
 
PROCEDURE DIVISION.
MAIN-PROCESSING.
    DISPLAY "=== ALLOCATE Statement Demonstration ===".
    DISPLAY " ".
    
    PERFORM DEMONSTRATE-BASIC-ALLOCATION
    PERFORM DEMONSTRATE-VARIABLE-LENGTH-ALLOCATION
    PERFORM DEMONSTRATE-BUFFER-MANAGEMENT
    PERFORM DEMONSTRATE-MEMORY-CLEANUP
    
    DISPLAY " ".
    DISPLAY "ALLOCATE demonstration completed".
    STOP RUN.
 
DEMONSTRATE-BASIC-ALLOCATION.
    DISPLAY "1. Basic Memory Allocation:".
    DISPLAY "   =========================".
    
    *> Allocate customer record
    ALLOCATE CUSTOMER-RECORD INITIALIZED RETURNING CUSTOMER-POINTER.
    ADD LENGTH OF CUSTOMER-RECORD TO WS-TOTAL-ALLOCATED.
    ADD 1 TO WS-ALLOCATION-COUNT.
    
    IF CUSTOMER-POINTER NOT = NULL
        DISPLAY "   Customer record allocated successfully"
        
        *> Set address and use the memory
        SET ADDRESS OF CUSTOMER-RECORD TO CUSTOMER-POINTER
        MOVE "CUST001" TO CUST-ID
        MOVE "JOHN SMITH" TO CUST-NAME
        MOVE 1500.75 TO CUST-BALANCE
        MOVE "ACTIVE" TO CUST-STATUS
        
        DISPLAY "   Customer ID: " CUST-ID
        DISPLAY "   Customer Name: " CUST-NAME
        DISPLAY "   Balance: $" CUST-BALANCE
        DISPLAY "   Status: " CUST-STATUS
    ELSE
        DISPLAY "   ERROR: Customer record allocation failed"
    END-IF.
    
    DISPLAY " ".
 
DEMONSTRATE-VARIABLE-LENGTH-ALLOCATION.
    DISPLAY "2. Variable-Length Allocation:".
    DISPLAY "   =============================".
    
    *> Calculate size for variable number of transactions
    MOVE 5 TO WS-ITEM-COUNT.
    COMPUTE WS-ALLOCATION-SIZE = 
        LENGTH OF TRANS-HEADER + (WS-ITEM-COUNT * LENGTH OF TRANS-ITEMS(1)).
    
    ALLOCATE WS-ALLOCATION-SIZE CHARACTERS RETURNING TRANSACTION-POINTER.
    ADD WS-ALLOCATION-SIZE TO WS-TOTAL-ALLOCATED.
    ADD 1 TO WS-ALLOCATION-COUNT.
    
    IF TRANSACTION-POINTER NOT = NULL
        DISPLAY "   Transaction record allocated: " WS-ALLOCATION-SIZE " bytes"
        
        *> Set address and initialize
        SET ADDRESS OF TRANSACTION-RECORD TO TRANSACTION-POINTER
        MOVE WS-ITEM-COUNT TO TRANS-COUNT
        MOVE 0 TO TRANS-TOTAL
        
        *> Populate transaction items
        PERFORM VARYING WS-COUNTER FROM 1 BY 1 
                UNTIL WS-COUNTER > WS-ITEM-COUNT
            STRING "TRANS" WS-COUNTER DELIMITED BY SIZE 
                   INTO TRANS-ID(WS-COUNTER)
            COMPUTE TRANS-AMOUNT(WS-COUNTER) = WS-COUNTER * 100.50
            ADD TRANS-AMOUNT(WS-COUNTER) TO TRANS-TOTAL
        END-PERFORM
        
        DISPLAY "   Transaction count: " TRANS-COUNT
        DISPLAY "   Total amount: $" TRANS-TOTAL
        
        *> Display some transaction details
        PERFORM VARYING WS-COUNTER FROM 1 BY 1 
                UNTIL WS-COUNTER > 3
            DISPLAY "   " TRANS-ID(WS-COUNTER) ": $" TRANS-AMOUNT(WS-COUNTER)
        END-PERFORM
    ELSE
        DISPLAY "   ERROR: Transaction record allocation failed"
    END-IF.
    
    DISPLAY " ".
 
DEMONSTRATE-BUFFER-MANAGEMENT.
    DISPLAY "3. Dynamic Buffer Management:".
    DISPLAY "   ===========================".
    
    *> Allocate dynamic buffer
    ALLOCATE DYNAMIC-BUFFER RETURNING BUFFER-POINTER.
    ADD LENGTH OF DYNAMIC-BUFFER TO WS-TOTAL-ALLOCATED.
    ADD 1 TO WS-ALLOCATION-COUNT.
    
    IF BUFFER-POINTER NOT = NULL
        DISPLAY "   Dynamic buffer allocated successfully"
        
        *> Set address and initialize buffer
        SET ADDRESS OF DYNAMIC-BUFFER TO BUFFER-POINTER
        MOVE LENGTH OF BUFFER-DATA TO BUFFER-SIZE
        
        *> Fill buffer with sample data
        MOVE "This is a dynamically allocated buffer containing sample data for testing memory management operations in COBOL." TO BUFFER-DATA
        
        DISPLAY "   Buffer size: " BUFFER-SIZE " bytes"
        DISPLAY "   Buffer content: " BUFFER-DATA(1:50) "..."
    ELSE
        DISPLAY "   ERROR: Dynamic buffer allocation failed"
    END-IF.
    
    DISPLAY " ".
 
DEMONSTRATE-MEMORY-CLEANUP.
    DISPLAY "4. Memory Cleanup and Deallocation:".
    DISPLAY "   =================================".
    
    *> Free allocated memory
    IF CUSTOMER-POINTER NOT = NULL
        FREE CUSTOMER-RECORD
        SET CUSTOMER-POINTER TO NULL
        DISPLAY "   Customer record deallocated"
    END-IF.
    
    IF TRANSACTION-POINTER NOT = NULL
        FREE TRANSACTION-RECORD
        SET TRANSACTION-POINTER TO NULL
        DISPLAY "   Transaction record deallocated"
    END-IF.
    
    IF BUFFER-POINTER NOT = NULL
        FREE DYNAMIC-BUFFER
        SET BUFFER-POINTER TO NULL
        DISPLAY "   Dynamic buffer deallocated"
    END-IF.
    
    DISPLAY "   Memory cleanup completed".
    DISPLAY "   Total allocated: " WS-TOTAL-ALLOCATED " bytes".
    DISPLAY "   Allocation count: " WS-ALLOCATION-COUNT.
    DISPLAY " ".

Best Practices and Guidelines

Recommended Practices

Always check if allocation was successful before using memory
Use INITIALIZED option to ensure clean memory state
Pair every ALLOCATE with a corresponding FREE statement
Set pointers to NULL after freeing memory
Calculate variable-length sizes carefully to avoid overruns
Monitor total memory allocation to prevent memory leaks
Use meaningful names for BASED variables and pointers
Document memory allocation patterns and lifecycle

Common Pitfalls

Memory leaks from unmatched ALLOCATE/FREE operations
Using memory after it has been freed (dangling pointers)
Not checking allocation success before memory access
Incorrect size calculations for variable-length structures
Forgetting to initialize allocated memory when needed
Not setting pointers to NULL after freeing memory
Attempting to free the same memory multiple times
Poor error handling for allocation failures

Related COBOL Concepts

FREE - Memory deallocation statement
BASED - Based variable definition for dynamic structures
POINTER - Pointer data type for memory addresses
SET ADDRESS - Address assignment for BASED variables
NULL - Null pointer constant
LENGTH OF - Size calculation for memory allocation
OCCURS DEPENDING ON - Variable-length array definition
RETURNING - Pointer return specification in ALLOCATE