Cs 1114 - lecture-29

Instructor : Muhammad Haris

All Rights Reserved to Department of Computer Science – GCU Lahore

Programming Fundamentals

Input and Output

Programming Fundamentals | Lecture-29 2

RAMRAM

Program Data

What is a Stream?

In DictionaryNoun: A flow of water in a channel (ندی)Verb: To come or go in large numbers

In Programming LanguagesAn abstract representation of “input data source”

or “output data destination”○ A stream hides all the underlying details of an input

source or output destination from a ProgramThe program treats it like an actual input data source or

output data destination

Example: cin and cout


Input and Output


RAMRAM

Program Data

stream stream

stream stream

“Stream” Concept Advantage A program handles all kinds of streams in

exactly the same wayFor Input, whether a stream is opened from

keyboard or from a file or from mic○ The program is only concerned with data which

it will extract from the streamFor output, whether a stream is opened from

monitor, file, or speaker○ The program is only concerned with data which

it will insert into the stream to be outputted


Working with Streams Steps to perform

Create a StreamConnect (or open) it to an input source or

output destinationDisconnect (or close) it when you are done

Characteristics of a Stream1. Input / Output Mode

- Input only, Output Only or both

2. Input or Output Entity it can connect to

3. Transfer mode- Text or binary


Standard Streams You’ve already been working with two

standard streamsConsole Input: named as cinConsole Output: named as cout

Did you perform required steps for these streams?No, because when you include <iostream> in

your program, they are done automatically

Two other standard streamsConsole Error (cerr) and Console Log (clog)


Operators for Streams

Stream Extraction Operator (>>)Which extracts input data from the stream

and save it in program memory○ Stream Name >> Variable Name

Example: cin >> number;

Stream Insertion Operator (<<)Which picks data from program memory and

inserts it to a stream to be outputted○ Stream Name << Variable Name

Example: cout << number;


What is a File? An external collection of related data

treated as a unit (stored with a single name) Purpose

To keep record of data permanently○ Contents of Primary Memory (RAM) are not

permanent○ Variables declared in a program are destroyed

when program terminates○ Collection of data is often too large to reside

entirely in main memory at one time


Types of Files

Text (Human readable)Everything is stored as characters whether it is

an integer or float valueEach line of data ends with a newline characterThere is a special character called end-of-file

(EOF) at the end of file.

Binary (Not human readable)Data is stored in exactly the same format as it

is stored in memory We’ll work with text (sequential) files in this course


Working with Files To treat file as an input source or as an

output destination in our programWe just need a stream because our program

can conveniently work with streams We’ll need to perform the necessary

steps this time because file streams are not standard streams i.e,.Create a streamOpen itClose it finally


File Streams

Three typesInput only – ifstreamOutput only – ofstreamBoth input and output – fstream

To use them we need to include <fstream>


1. Creating File Stream

SyntaxTypeName<space>identifierExamples

○ ifstream fInputStream;○ ofstream fOutputStream;○ fstream fInOutStream;


2. Connecting Stream to File

SyntaxIdentifier.open(“filePath”);Examples

○ fInputStream.open(“abc.txt”);// file abc.txt in the same folder

○ fOutputStream.open(“C:\\xyz.txt”);// complete path of the file

○ fInOutStream.open(“abc.txt”);


File Input/Output When a stream is created and

connected to a file for output, it is same like console output stream for a programfOutputStream << aString;fInputOutputStream << aString;

When a stream is created and connected to a file for input, it is same like console input stream for a programfInputStream >> aString;fInputOutputStream >> aString;


File Marker

An indicator in a file stream thatDetermines the position from which data

should be read or to which data should be written in a file

When a file is opened for input or output, it is always positioned at the beginning of the file


Handling Errors

Ensure the file stream is opened before proceeding further

Ensure the file stream is properly closed so system resources are freed up

See FileDemo2.cpp


Structure of Data in Files

C++ imposes no structure on a fileYou can put data in a file the way you wantThe concept of a record doesn’t not exist

The programmer must structure files to meet the application's requirementsFor example, you can save each record on a

separate line in a text file and can use “separator character” to separate different data items within a record

See RecordsInFile.cpp


Updating a Text File

The process is not straightforward, as file marker is always positioned at the beginning when you reopen a fileEither to add another record in it or to

update an existing oneThere are functions to change to the

position of File Marker but moving it to a right position is not possible in text files


How to Update?

Read all the records in program memory Add or update Save all the existing along with new or

updated ones in a temporary file Delete the old file Rename temporary file as the old one


Task (to be done by next lecture)

After writing records to a file, read all records from the file and display them where each item in a record should be separately outputExample

○ For each record (read from file), show like thatAccount No: Name:Balance:


Technology

Cs 1114 - lecture-29