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COBOL Tutorial

COBOL START Statement

The START statement in COBOL positions a file at a specific record based on a key value, without reading that record. START is used with indexed and relative files to position the file pointer at a record matching specified key criteria. After START, subsequent READ operations begin from that position, enabling efficient positioned access and sequential processing from specific key values.

START is essential for indexed file processing when you need to begin reading from a specific key value rather than from the beginning of the file. Understanding START is crucial for efficient file navigation and positioned sequential access in COBOL programs.

Basic START Syntax

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       START file-name
           KEY IS {EQUAL TO | GREATER THAN | NOT LESS THAN} key-value
           [INVALID KEY statements]
           [NOT INVALID KEY statements]
       END-START

Simple START Example

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       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT CUSTOMER-FILE ASSIGN TO "CUSTOMER.DAT"
               ORGANIZATION IS INDEXED
               ACCESS MODE IS SEQUENTIAL
               RECORD KEY IS CUSTOMER-ID
               FILE STATUS IS FILE-STATUS-CODE.
       
       DATA DIVISION.
       FILE SECTION.
       FD  CUSTOMER-FILE.
       01  CUSTOMER-RECORD.
           05  CUSTOMER-ID     PIC 9(8).
           05  CUSTOMER-NAME   PIC X(30).
       
       WORKING-STORAGE SECTION.
       01  FILE-STATUS-CODE    PIC X(2).
       01  SEARCH-KEY          PIC 9(8) VALUE 50000000.
       
       PROCEDURE DIVISION.
       MAIN-LOGIC.
           OPEN INPUT CUSTOMER-FILE
           
           *> Position file at customer ID 50000000
           START CUSTOMER-FILE
               KEY IS GREATER THAN SEARCH-KEY
               INVALID KEY
                   DISPLAY "No records found with key > " SEARCH-KEY
               NOT INVALID KEY
                   DISPLAY "Positioned at key > " SEARCH-KEY
                   *> Read records sequentially from this position
                   PERFORM READ-SEQUENTIAL-RECORDS
           END-START
           
           CLOSE CUSTOMER-FILE
           STOP RUN.
       
       READ-SEQUENTIAL-RECORDS.
           PERFORM UNTIL FILE-STATUS-CODE = "10"
               READ CUSTOMER-FILE NEXT RECORD
                   AT END
                       CONTINUE
                   NOT AT END
                       DISPLAY "Customer: " CUSTOMER-ID " " CUSTOMER-NAME
               END-READ
           END-PERFORM.

START Key Operators

  • EQUAL TO: Position at exact key match
  • GREATER THAN: Position at first record with key greater than specified value
  • NOT LESS THAN: Position at first record with key greater than or equal to specified value

Complete START Example

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. START-EXAMPLE.
       
       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT PRODUCT-FILE ASSIGN TO "PRODUCT.DAT"
               ORGANIZATION IS INDEXED
               ACCESS MODE IS DYNAMIC
               RECORD KEY IS PRODUCT-CODE
               FILE STATUS IS FILE-STATUS-CODE.
       
       DATA DIVISION.
       FILE SECTION.
       FD  PRODUCT-FILE.
       01  PRODUCT-RECORD.
           05  PRODUCT-CODE    PIC X(10).
           05  PRODUCT-NAME    PIC X(30).
           05  PRODUCT-PRICE   PIC 9(6)V99.
       
       WORKING-STORAGE SECTION.
       01  FILE-STATUS-CODE    PIC X(2).
       01  START-KEY           PIC X(10) VALUE "PROD-0500".
       01  RECORD-COUNT        PIC 9(4) VALUE 0.
       
       PROCEDURE DIVISION.
       MAIN-LOGIC.
           DISPLAY "=== START Statement Example ==="
           
           OPEN INPUT PRODUCT-FILE
           
           IF FILE-STATUS-CODE = "00"
               *> Position at products starting with PROD-0500
               START PRODUCT-FILE
                   KEY IS NOT LESS THAN START-KEY
                   INVALID KEY
                       DISPLAY "No products found starting at " START-KEY
                   NOT INVALID KEY
                       DISPLAY "Positioned at products >= " START-KEY
                       PERFORM READ-PRODUCTS-FROM-POSITION
               END-START
           ELSE
               DISPLAY "ERROR: Cannot open file. Status: " FILE-STATUS-CODE
           END-IF
           
           CLOSE PRODUCT-FILE
           DISPLAY "Records processed: " RECORD-COUNT
           STOP RUN.
       
       READ-PRODUCTS-FROM-POSITION.
           PERFORM UNTIL FILE-STATUS-CODE = "10"
               READ PRODUCT-FILE NEXT RECORD
                   AT END
                       CONTINUE
                   NOT AT END
                       IF FILE-STATUS-CODE = "00"
                           ADD 1 TO RECORD-COUNT
                           DISPLAY "Product: " PRODUCT-CODE 
                                   " " PRODUCT-NAME " $" PRODUCT-PRICE
                       ELSE
                           DISPLAY "Read error. Status: " FILE-STATUS-CODE
                           EXIT PERFORM
                       END-IF
               END-READ
           END-PERFORM.

Best Practices for START

  • Always handle INVALID KEY: Check for positioning failures
  • Check FILE STATUS: Verify successful positioning
  • Validate key values: Ensure keys are valid before START
  • Use appropriate operators: Choose EQUAL TO, GREATER THAN, or NOT LESS THAN based on needs
  • Use with READ NEXT: START positions, READ NEXT retrieves

Explain Like I'm 5: START

Think of START like using a bookmark:

  • START is like putting a bookmark at a specific page
  • READ NEXT is like reading from that bookmark forward
  • Key operators are like different ways to find the page (exact page, after page 50, etc.)

So START is like bookmarking a specific place in a file, then reading from there!

Test Your Knowledge

1. What does START do?

  • Reads a record
  • Positions the file at a specific key without reading
  • Opens a file
  • Closes a file

2. What file types can use START?

  • Sequential files only
  • Indexed and relative files
  • All file types
  • Only VSAM files

3. What key operators can you use with START?

  • Only EQUAL TO
  • EQUAL TO, GREATER THAN, NOT LESS THAN
  • Only GREATER THAN
  • No operators

4. What should you do if START doesn't find a match?

  • Continue anyway
  • Handle INVALID KEY condition
  • Read anyway
  • Close the file