HANDLING COMPUTER FILES

HANDLING COMPUTER FILES

FILE CONTENTS

All information in a file is always in binary form or a series of ones and zeros. A document includes any file you have created. It can be a true text document, sound file, graphics, images, or any other type of information the computer can create, store, or size from the internet.

PROGRAM FILES

They contain instructions for the computer’s microprocessor and tell the computer what to do.

DATA FILES: These include all other files on disk that are not exactly programs or documents. These include support files for programs, temporary files, and other random stuff that must be saved inside the computer.

SEMANTICS

Although the way programs manipulate files varies according to the operating system and file system involved, the following operations are typical:

(i) Creating a file with a given name.

(ii) Setting attributes that control operations on the file.

(iii) Opening a file to use its content.

(iv) Reading or updating the content.

 (v) Committing updated contents to durable storage

Closing the file, thereby losing access until it is opened again.

IDENTIFYING AND ORGANIZING FILES

In modern computer system, files are typically accessed using names also known as file name. Most computers organize files into hierarchies using folders, directories or catalogs. The concept is the same irrespective of the terminology used. Each folder can contain an arbitrary number of files, and it can also contain other folders. These other folders are referred to as sub folders. Sub folders can contain still more files and folders and so on, thus building a tree – like structure in which one “master folder” can contain any number of levels of other folders and files.

BASIC FILE OPERATIONS

The basic file operations are: 

(i)                 Create (The act of making new file).

(ii)               Delete (To remove a file from a disk).

(iii)             Retrieve (To find a file and bring it back).

(iv)             Copy (To produce something so that it is the same as an original piece of work)

(v)               View (See the file in a folder).

(vi)             Update (To make something more suitable for use now by adding new information or changing design).

(vii)           Open (To open a file for editing).

(viii)         Close (To close the edited file).  

CREATING A SEQUENTIAL FILE

These are the ways to organize data in a sequential file:

1.      Choose a DOS file name. Some examples are INCOME.86, CUSTOMER.DAT and FORT500.

2.      Choose a number from 1 through 255 to be the reference number of the file. While the file is in use, it will be identified by this number.

3.      Execute the statement

OPEN filename FOR OUTPUT AS #n

Where n is the reference number.

4.      Place data into the file with the WRITE*statement. If a$ is a string, then the statement

WRITE #n, a$

writes  string a$ surrounded by quotation marks into the file . If c is a number then the statement

WRITE #n, c

writes the number c, without any leading or trailing spaces, into file number n. The statement

WRITE #n, a$, c

writes a$ and c as before, but comma separating them. Similarly, if the statement WRITE*n is followed by a list of several strings and / or numbers separated by commas, then all the string and numbers appear as before, separated by  commas. After each WRITE* statement is executed, the characters f and El are placed into the file. 

5.      After all the data have been recorded in the file, execute

CLOSE #n

Where n is the reference number. This statement breaks the communication line with the file and dissociates the number n from the file.

Example: Write a program to create the file. Use EOD as a sentinel to indicate that all the data has been read.

Solution

REM Create the file YOB.DAT and record some data into it

OPEN “YOB.DAT” FOR OUTPUT AS #1

READ name$, year

DO WHILE name$, year <> “EOD”

WRITE #1, name$, year

READ name$, year LOOP

CLOSE #1

REM ----Data: name, year of birth

DATA Barbra, 1942

DATA Ringo, 1940

DATA Sylvester, 1946

DATA EOD, 0

END