File Processing
















File Processing


All file processing operations are held in procedure division.
 File Operations:  OPEN
		   READ
	  	   WRITE
		   REWRITE
		   CLOSE


OPEN EMPFILE:
OPEN {INPUT, OUTPUT, EXTEND, I-O} file-name-1 [, file-name-2] . . .


The OPEN statement initiates the processing of files. The success-
ful execution of an OPEN statement determines the availability of 
the file for processing. The successful execution of the OPEN 
statement makes the associated record area available to the program; 
it does not obtain or release the first data record. If the FILE 
STATUS clause is specified in the FILE-CONTROL entry, the associa-
ted operation status is updated when the OPEN statement is executed.


A sequential file can be opened in one of the following four modes. 
INPUT, OUTPUT, EXTEND and I-O.

A file can be opened in the INPUT mode only if it already exists. 
Such a file becomes an input file from which records can be read 
sequentially.

When a file is to be created for the first time, it must be opened 
in the OUTPUT mode. File can be written in this mode.

The EXTEND mode also opens a file for writing, but the file pointer 
is positioned after the end of the last record. Thus any records 
written will get appended to the file.

A file is opened in the I-O mode when it needs to be updated. This 
mode provides both reading and rewriting of records.



CLOSE EMPFILE:

This statement terminates processing of file. In COBOL-85 this 
CLOSE Statement is optional and STOP RUN automatically closes the 
File if it is not explicitly closed. This CLOSE statement means 
termination of link between Physical file and logical file.


READ EMPFILE:

If a file is opened in INPUT or I-O mode then a READ statement 
make available Next logical record for processing. The primary 
function of the READ statement is to fetch records from a file 
and place the file pointer at an appropriate position after READ; 
it performs certain checks to ensure proper execution of the 
program.


READ EMPFILE 
            AT END imperative statement.
END-READ


If the file reached end of the file and if program tries to read 
a record then AT END condition satisfy and imperative statement 
will performed.


If INTO condition specified like READ EMPFILE INTO WS-RECORD.
Here WS-RECORD is data division data name. Program read the file 
and places record into WS-RECORD.


WRITE statement:

WRITE CAPGEMINI-REC FROM WS-RECORD
END-WRITE.


File opened in OUTPUT or EXTEND mode then we can use WRITE state-
ment to write records into the file. If from is used then the data 
in WS-RECORD is moved to record and writing take place. If FROM 
is omitted then Data moved to record name will be written into 
file. If we are reading file we refer file name in READ statement,
where as while writing we refer record name with WRITE command.



REWRITE statement:

REWRITE command is used to update a record in a file. If file is 
opened in I-O mode then only we can use REWRITE command on that 
file. This REWRITE is not available in Sequential file. Before 
using REWRITE command, corresponding record should be read. 


A Sample COBOL Program that READ a Sequential files and Write 
into another file.



 Click here to see sample cobol program