files handing

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FILE HANDLING
Basic terms in file handling:
1. Files
2. Records
3. Fields.
4. Physical file.
4. Logical files.
FILES: it is collect of records.    Ex: student file, employments file.
RECORDS: it is collect of fields that are used to describe an entity. One or more fields from together are called records.     Ex: student ID, student name.
FIELDS:  A set of characters are combined together called as information.
PHYSICAL FILE: it is the information that exists on the external device. It is known as external devices.
LOGICAL FILE: it is the information that is used by the program. In COBOL program one file can be handled at one time only.
Difference between physical and logical file:

Physical file
Logical file
1.      Occupies the portion of memory. It contains the original data.
2.      It contains 1 record format.
3.      Can exist even without logical file.
4.      If there is a logical file for physical file, the physical file can’t delete until and unless we delete logical file.
1.      Does not occupy any memory space.  Does not contain any data.it loads itself at run time as per the defined access path.
2.      It contains 16 record formats.
3.      Can’t exist without physical file.
4.      If there is a logical file for a physical file, the logical file can be deleted without delete the physical file.
.

Files are identified by file name.
Records are identified by record name.
Fields are identified by field’s name.
WORKING WITH FILES:
1. Declaration of files.
2. Processing of files.

Declaration of files is done in environment and data division.
Processing of files is done in procedure division.
Declaration of files:
ENVIRONMENTAL DIVISION.
INPUT-OUTPUT SECTION
FILE CONTROL
               SELECT LOGICAL FILE NAME ASSIGN TO PHYSICAL NAME.
              ORGANIZATION IS SEQUENTICAL/INDEXED/RELATIVE.
            ACCESS MODE IS SEQUENTICAL/DYNAMIC/RANDOM.
            RECORD KEY/RELATIVE KEY IS ----------------------.
            FILE STATUS IS FS.
DATA DIVISION.
FILE SECTION.
FD LOGICIAL FILE NAME.
01 TR-DATA-FILE.
       02 NAME PIC X(09).
WORKING STORAGE SECTION.
01 WS-FS PIC X(01).

Processing of files.
STEPS
1. OPEN THE FILE.
2. LOGICAL OPERATON LIKE WRITE, READ, REWRITE, UPDATE.
3. CLOSE THE FILE.
OPENING MODES:
INPUT MODE: READ (READ DATA FROM THE FILE).
OUTPUT MODE: WRITE (WRITE THE DATA INTO THE FILE).
INPUT-OUTPUT MODE: READ AND REWRITE (UPDATE). AND DELETE.
EXTEND MODE: WRITE (APPEND THE RECORD).

PROCEDURE DIVISION.
OPEN MODE LOGICAL FILE NAME.
LOGICAL FOR WRITE/READ/REWRITE.
CLOSE LOGICAL FILE.








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