Input and output in C++

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By
Nilesh Dalvi
LLeeccttuurreerr,, PPaattkkaarr--VVaarrddee CCoolllleeggee..
http://www.slideshare.net/nileshdalvi01

Introduction
• Every program takes some data as input and
generates processed data as output.
• C++ supports set of I/O functions.
• C++ uses the concepts of stream and stream
classes to implement its I/O operations with console
and disk files.
• In this chapter we will discuss how stream classes
support the console-oriented I/O operations.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

Streams in C++
• Stream is a sequence of bytes.
• If data is received from input devices in
sequence then it is called as source stream.
• When data is passed to output devices then
it is called destination.
• The data is received from keyboard or disk
and can be passed on to monitor or to the
disk.

Streams in C++
Streams in I/O devices

Streams in C++
• Data in source stream can be used as input
data by program .
• Source stream is called as input stream.
• Destination stream that collects output data
from the program is known as output
stream.

Streams in C++
Input and output streams

Streams Classes
• C++ streams based are based on class and
object theory.
• C++ has a number of stream classes that
are used to work with console and file
operations.
• These classes are known as streams classes.
• All these classes are declared in the header
file <iostream>.

Streams Classes
Hierarchy of streams classes

Streams Classes
• Classes istream and ostream are derived
classes of base class ios.
• streambuf handles the buffer by providing
the facilities to flush and pour the buffer.
• iostream is derived from classes istream
and ostream by using multiple inheritance.
• ios class is a virtual class which avoid
ambiguity
• ios class has an ability to handle formatted
and unformatted I/O operations.

Streams Classes
Class Name Contents
ios • Contains basic facilities that are used by all
other input and output classes
istream • Inherits properties of ios.
• Declares input function get(), getline(), read().
• Contains overloaded extraction >> operator
ostream • Inherits properties of ios.
• Declares input function put(), write().
• Contains overloaded insertion << operator
iostream • Inherits properties of ios, istream and ostream.

Unformatted console I/O operations
Input and output streams
• Input stream uses cin object to read data
• Output stream uses cout object to display
data on the screen.
• Data type is identified by these functions
using operator overloading << (insertion)
and >> (extraction).
• The >> operator is overloaded in istream
class
• The << operator is overloaded in ostream
class

Working of cin and cout statements

Input Stream
• It does read operation through keyboard.
• It uses cin object.
• cin statement uses >> operator before
variable name.
• Syntax:
cin >> variable;
• Example:
int weight;
cin >> weight;

Output Stream
• It displays the contents of variables on the
screen.
• It uses cout object.
• cout statement uses << operator before
variable name.
• Syntax:
cout << variable;
• Example:
int weight;
cout << weight;

get() and put()
• The single character input and output
operations in C++ can be done with get()
and put() functions.
• get() – reads character.
• put() – display the character.

The get() has two syntaxes.
• get(char) – assigns the input character to its
argument.
char c;
cin.get(c); //get char from keyboard.
while(c != 'n')
{
cout << c; //display char on screen.
cin.get(c); //get another char.
}

The get() has two syntaxes.
• get(void) – returns the input character.
char c;
c = cin.get();
value returned by function get() is assigned
to c.

• The function put() can be used to output a
line of text, character by character.
cout.put(‘X’);
• Displays the character X.
cout.put(68);
• This statement will convert int value 68 to
char value and display the character
whose ASCII value is 68.

Character I/O with get() and put()

getline() and write() functions:
• Displays a line of text by using line-oriented I/O
functions getline() and write().
• getline()- reads a whole line of text that ends
with a newline character(‘n’).
• Invoked by using object cin as follows:
cin.getline (line, size);
• Reading is terminated as the newline char ‘n’
is encountered or size-1 characters are read.
• Newline character is read but not saved.
• Instead, it is replaced by null character.

Reading Strings with getline()

• write() function displays an entire line and
has the following form:
cout.write (line, size);
• line – represents the name of the string to
be displayed .
• size - indicates number of characters to
display.

Displaying String with write()

Formatted Console I/O Operations
• C++ provides various formatted console I/O
functions for formatting the output.
1. ios class functions and flags.
2. Manipulators
3. User-defined output functions
• ios grants operations common to both input
and output.

Function Working
width() To set required field width. o/p will be displayed with
given width.
precision() To set number of decimal point for a float value.
fill() To set character to fill in the blank space of the field.
setf() To set various flags for formatting output.
unsetf() To remove the flags setting
Table: ios class functions

Fig: Formatted functions with cout object

Defining field width: width()
• width() – defines width of a field necessary
for the output of an item.
cout.width (w);
• w - field width(number of columns).
• Output will be printed in a field of w
characters wide at the right end of the field.
• Field width should be specified for each
item separately.

• For example, the statements
cout.width(5);
cout<<543<<12<<"n";
will produce following output:
5 4 3 1 2
• 543 is printed right-justified in the first five
columns.
• width(5) does not retain the setting for
printing the 12.

cout.width(5);
cout<<543;
cout.width(5);
cout<<12<<"n";
This produce the following output:
5 4 3 1 2
• C++ never truncates the values and
• If the specified width is smaller than the size of
the value, C++ expands the field to fit the
value.

Specifying field size with width()

Setting precision : precision()
• Default floating numbers are printed
with six digits after the decimal point.
• precision() – specifies number of digits
to be displayed after the decimal
point while printing the floating-point
numbers, has the form:
cout.precision(d);
• d is the number of digits to the right of
the decimal point.

• For Examples:
cout.precision(3);
cout<<1.23456<<”n”;
cout.precision(4);
cout<<3.14159<<”n”;

width() and precision()
• We can also combine the field
specification with the precision setting.
Example:
cout.precision(2);
cout.width(5);
cout<<1.2345;
• The output will be:
1 . 2 3

Filling and Padding :fill()
• We can use the fill() function to fill the
unused positions by any desired
character.
• It is used in the following form:
cout.fill(ch);
• where ch represents the character
which is used for filling the unused
positions.

Filling and Padding :fill()
• For Example:
cout.fill(‘*’);
cout.width(10);
cout<<5250<<"n“;
• The output would be:
* * * * * * 5 2 5 0
• Financial institutions and banks use this kind
of padding while printing cheques so that
no one can change the amount easily.

Formatting flags, bit-fields and setf()
• setf() function can be used as follows:
cout.setf(arg1,arg2);
• arg1- one of the formatting flags defined in
the class ios.
• It specifies the format action required for
the output.
• arg2- Another ios constant known as bit
field specifies the group to which the
formatting flag belongs.

Table : Format-state-flags
Flag Bit Field Flag Purpose
ios::left
ios::right Right-Justify all Output
ios::adjustfield
ios::internal Left-Justify sign or Base indicator and
Left-Justify all Output
right-justify rest of the number
ios::dec
ios::basefield
Displays integer in base 10(decimal)
format
ios::oct Displays integer in base 8(octal)
format
ios::hex Displays integer in base
16(hexadecimal) format
ios::fixed
ios::floatfield
Use fixed point notation when
displaying floating point numbers
ios::scientific Use exponential notation when
displaying floating point numbers

• Consider the following segment of code:
cout.fill(‘*’);
cout.setf(ios::left,ios::adjustfield);
cout.width(10);
cout<<"TABLE 1"<<"n";
• This will produce the following output:
T A B L E 1 * * *

• The statements
cout.fill('*');
cout.precision(3);
cout.setf(ios::internal,ios::adjustfield);
cout.setf(ios::scientific,ios::floatfield);
cout.width(15);
cout<<-12.34567<<“n”;
• will produce the following output:
- * * * * * 1 . 2 3 5 e + 0 1

Displaying Trailing Zeros And Plus Sign
• If we print the numbers 10.75, 25.00 and
15.50 using,
cout.width(8);
cout.precision(2);
• Then output will be as follows:
1 0 . 7 5
2 5
1 5 . 5
• The trailing zeros in the second and third
items have been truncated.

• The above output would look better if they
are printed as follows:
10.75
25.00
15.50
• setf() can be used with the flag
ios::showpoint as a single argument to
achieve this form of output.
• For example,
cout.setf(ios::showpoint);
• which display tailing zeros

• plus sign can be printed before a positive
number using the following statement:
cout.setf(ios::showpos);
• showpoint and showpos do not have any
bit fields and therefore are used as single
arguments in setf().

cout.setf(ios::showpoint);
cout.setf(ios::showpos);
cout.precision(3);
cout.setf(ios::fixed,ios::floatfield);
cout.setf(ios::internal,ios::adjustfield);
cout.width(10);
cout<<275.5<<"n";
• will produce the following output:
+ 2 7 5 . 5 0 0

Flag Lists
• Following table lists the flags that do
not posses a named bit field:

Formatting with flags in setf()

Managing output with manipulators:
• The header file iomanip provides a set of
functions called manipulators which can be
used to manipulate the output formats.
• Two or more manipulators can be used as a
chain in one statement as shown below:
cout<<manip1<<manip2<<manip3<<item;
cout<<manip1<<item1<<manip2<<item2;

• The most commonly used manipulators are
shown in table.

• One statement can be used to format output
for two or more values.
• For example, the statement
cout<<setw(5)<<setprecision(2)<<1.2345
<<setw(10)<<setprecision(4)<<sqrt(2)
<<setw(15)<<setiosflags(ios::scientific)
<<sqrt(3)<<endl;
• Will print all the three values in one line with the
field size of 5,10,and 15 respectively.

• We can jointly use the manipulators and the
ios functions in a program:
cout.width(5);
cout<<setprecision(2)<<1.2345
<<setw(10)<<setprecision(4)<<sqrt(2)
<<setw(15)<<setiosflags(ios::scientific)
<<sqrt(3)<<endl;

Designing Our Own Manipulators
• General form for creating a manipulator is:
ostream & manipulator(ostream & output)
{
.....
.....(code)
.....
return output;
}
• Here, the manipulator is the name of the
manipulator

• The following function defines a manipulator
called unit that displays "inches":
ostream & unit(ostream & output)
{
output<<"inches";
return output;
}
• The statement
cout << 36 << unit;
• will produce the following output
36 inches

• We can also create manipulators that could
represent a sequence of operations. Example:
ostream & show(ostream & output)
{
output.setf(ios::showpoint);
output.setf(ios::showpos);
output<<setw(10);
return output;
}
• Manipulator show turns on the flags showpoint
and showpos and sets the field width to 10.

#include <iostream>
#include <iomanip>
ostream & curr(ostream & ostr)
{
cout<< setprecision(2);
cout<<”Rs. “;
return ostr;
}
int main()
{
float amt = 4.5476;
cout<<curr<<amt;
return 0;
}
//Output: Rs. 4.55

Input and output in C++

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