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Streams and IO

Streams are pipe like constructors used for

providing IO.

When a programmer needs to handle inputfrom or output to external entities,then

streams are used by c++.

The stream is the central concept of theiostream classes


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Output streams

An output stream object is a destination for bytes.

The three most important output stream classare

, and ostrstream.ofstream,ostream

The ostream class, through the derived class, supports the predefined streambasic_ostream

objects:cout standard output

cerr standard error with limited bufferingclog similar to cerrbut with full buffering
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Input streams

An input stream object is a source of bytes.

The three most important input stream

istrstream, andifstream,istreamclasses are

The istream class is best used for sequential

text-mode input. You can configure objects

of class istream for buffered or unbuffered

operation. All functionality of the base

class,ios, is included in istream. You will

rarelconstruct objects from class istream.

Instead, you will generally use the
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Formatting I/O

Formatting using Ios functions

Width()-It specifies the width for display.the output will take up thewidth specified.used in alignng vertical column of numeric items.

Precision()-It specifies the precision of the floating point

number.Default precision is six digits after decimal point Fill()-it specifies the character for filling up the unused prion of the

field.It is usually usd with the width member function.

Setf()-The function specifies the format flags that controls outputdisplay like left or right justification,padding after signsymbol,scientific notation display,displaying abse of the number

Unsetf()-This function provides undo operation for above mentionedoperations with setf.


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.The prototype of the function is

functionname

The functions set new value to the stream andretutn value.The width function sets new width to

the argument specified and returns old width.,Theprecision function sets new precision and returnsold precision.

Member functions of Ios


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I/O manipulators

Manipulators are special functions for

formatting

The choice between manipulators and ios

functions to solve formatting problemssometimes depends upon the user.

Equivalent manipulators for some of the io

functions are:Setw(),setprecision(),setfill(),setiosflags(),rese

tiosflags().


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Unlike Ios,manipulators do not return theprevious status

Manipulators can write our own manipulatorand use it in the programmarksheet printing

program can use it for printing

Ios functions are singleThey cannot becombined to have multiple effects

together.When a large set of formattingoptions are used,manipulators are used to

write and produce more readable code.Ios functions need whereas

manipulators need .

Difference between ios and manipulators


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#include #include

/*

* Input using cin

*/

int main () {

char myline[256];=

Example program


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Object Serialization


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Object Serialization

Simple persistence method which provides

a program the ability to read or write a whole

object to and from a stream of bytes

Allows Java objects to be encoded into a

byte stream suitable for streaming to a file

on disk or over a network

The class must implement the Serializable

interface (java.io.Serializable), which does

not declare any methods, and have

accessors and mutators for its attributes


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Object Serialization :example pgm

// create output stream

File file = new

File("teams_serialize.ser");String fullPath =

file.getAbsolutePath();

fos = newFileOutputStream(fullPath);

// open output stream and store


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Object persistence

One of the most critical tasks that

applications have to perform is to save and

restore data

Persistence is the storage of data from

working memory so that it can be restored

when the application is run again

In object-oriented systems, there are several

ways in which objects can be made

persistent

The choice of ersistence method is an


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C++ Namespaces

A mechanism for logically grouping

declarations and definitions into a common

declarative region


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C++ Namespaces

The contents of the namespace can be

accessed by code inside or outside the

namespace

Use the scope resolution operator to access

elements from outside the namespace

Alternatively, the usingdeclaration allows the

names of the elements to be used directly


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C++ Namespaces

Creating a namespacenamespace smallNamespace

{

int count = 0;void abc();

} //end smallNamespace

Using a namespace

usingnamespace smallNamespace;

count +=1;

abc();


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STD Namespaces

Items declared in the C++ Standard Library

are declared in the stdnamespace

C++ include files for several functions are inthe stdnamespace

To include input and output functions from the

C++ library, writeinclude

usingnamespace std;


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Ansi string objects

The ANSI string class implements a first-

class character string data type that avoids

many problems

associated with simple character arrays

("C-style strings"). You can define a string

object very

simply, as shown in the following example


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Ansi string class syntax pgm

#include

using namespace std;

...

string first_name = "Bjarne";string last_name;

last_name = "Stroustrup";

string names = first_name + " " + last_name;

cout


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Ansi string class member functions

Member functions

The string class defines many member functions. A few of the basicones are described below:

A string object may defined without an initializing value, in which caseits initial

value is an empty string (zero length, no characters):string str1;

A string object may also be initialized with

a string expression:

string str2 = str1;

string str3 = str1 + str2;string str4 (str2); // Alternate form

a character string literal:

string str4 = "Hello there";


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Standard Template Library

The standard template library (STL) containsContainers

Algorithms

Iterators

A containeris a way that stored data is

organized in memory, for example an array of

elements.

Algorithms in the STL are procedures that are

applied to containers to process their data, for

example search for an element in an array, or

sort an array.

C t i It t Al ith


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Containers, Iterators, Algorithm

Container

AlgorithmIterator

Container

Iterator

Algorithm

Objects

Iterator

Iterator

Algorithm

Algorithms use iterators to interact with objectsstored in containers


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Containers

A container is a way to store data, eitherbuilt-in data

types like int and float, or class objects

The STL provides several basic kinds ofcontainers

: one-dimensional array

: double linked list : double-ended queue

: queue

: stack

: set


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Sequence Containers

A sequence container stores a set ofelements in

sequence, in other words each element

(exceptfor the first and last one) is preceded byone

specific element and followed byanother, ,

and are sequentialcontainers

In an ordinary C++ array the size is


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Sequence Containers

is a double linked list (each elementhas

points to its successor and predecessor), it

isquick to insert or delete elements but has

slow

random access is a double-ended queue, that

means one

can insert and delete elements from both


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Associative Containers

An associative container is non-sequential

but uses

a keyto access elements. The keys,typically a number or a string, are used by

the container to arrange the stored elements

in a specific order,

for example in a dictionary the entries are

ordered

alphabetically.


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Associative Containers

A stores a number of items whichcontain keys

The keys are the attributes used to order the

items,for example a set might store objects of the

class

Person which are ordered alphabetically usingtheir name

A stores pairs of objects: a key object

and


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vector

array_

Iterators

Iterators are pointer-like entities that areused to

access individual elements in a container.

Often they are used to move sequentiallyfrom element to element, a process called

iteratingthrough a container.17

4

23

12

size_ 4

vector::iterator

The iterator corresponding tothe class vector is ofthe type vector::iterator


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Iterators

One can have multiple iterators pointing todifferent or identical elements in the

containervector v

array_ 17

4

23

12

size_ 4i3

i1

i2


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Iterators#include

#include

int arr[] = { 12, 3, 17, 8 }; // standard C array

vector v(arr, arr+4); // initialize vectorwith C array

for (vector::iterator i=v.begin();

i!=v.end(); i++)// initialize i with pointer to first element of v

// i++ increment iterator, move iterator to next

element


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File handling in C++

Introduction to File Handling

Data entered once, required later again

Same Data to be used by others

Data required again by the same program

Files and Streams


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I/O Streams

StreamDescription

cin

Standard input streamcout

Standard output stream

cerr

Standard error stream


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ofstream

Output file stream Class

open() is a member function of the class

ofstreamInherited functions of ofstream class, from

the class ostream are

put()

write()

seekp()

tellp()


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fstream

It supports files for simultaneous input and output

fstream is derived fromifstream

ofstream

iostream

They are parent classes and fstream is the child classMember functions of the class fstream

open

close

close all

seekg

seekp

tellg

tellp


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//This program creates a file called message.dat

#include //Required for file

I/Oint main()

{

ofstream myfile (message.dat);

If (!myfile)

{

//check if the file is

opened or notcout


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Function in C++Function Prototype

Function Call

Function Definition

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