Formatted Console IO Operations

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C++ supports a number of features that could be used for formatting the output. These features include:

  1. ios class functions and flags.
  2. Manipulators.
  3. User-defined output functions.

1. ios Class functions and flags

The ios class contains a large number of member functions that could be used to format the output in a number of ways. The most important ones among them are listed below.

FunctionSyntaxUse
width()cout.width(size);To specify the required field size for displaying an output value.
precision()cout.precision(2);To specify the number of digits to be displayed after the decimal point of a float value.
fill()cout.fill(‘character’);To specify a character that is used to fill the unused portion of a field.
setf()cout.setf(arg1, arg2);To specify format flags that can control the form of output display such as left or right justification.
unsetf()cout.resetiosflags()To clear the flags specified.
Formatted IO Functions

In setf() function we can provide one or two argument.

cout.setf(arg1, arg2);

The arg1 is formatting flags defined in the ios class, and arg2 is known as bit field specifies the group to which the formatting flags belong. The flags and bit field are shown below:

Format requiredFlag (arg1)Bit-field (arg2)
Left justified output Right justified output Padding after sign or base indicator (like +##20)ios::left ios::right   ios::internalios::adjustfield ios::adjustfield   ios::adjustfield
Scientific notation
Fixed point notation		ios::scientific ios::fixedios::floatfield
ios::floatfield
Decimal baseios::docios::basefield
Octal base
Hexadecimal base		ios::oct ios::hexios::basefield
ios::basefield

There some of the flags without bit fields are mentioned below:

FlagMeaning
ios::showbase
ios::showpos
ios::showpoint
ios::uppercase		Use base indicator on output.
Print + before positive numbers.
Show trailing decimal point and zeros.
Use uppercase letters for hex output.
ios::skipusSkip white space on input.
ios::unitbuf
ios::stdio		Flush all streams after insertion.
Flush stdout and stderr after insertion.

Example of ios functions:

#include <iostream> 
#include <math>
using namespace std; 
int main()
{
	cout.fill('*'); 
	cout.setf(ios::left,ios::adjustfield); 
	cout.width(10);
	cout<<"value"; 
	cout.setf(ios::right,ios::adjustfield); 
	cout.width(15);

	cout<<"SQRT OF VALUE"<<"\n";
	cout.fill('.'); 
	cout.precision(4); 
	cout.setf(ios::showpoint); 
	cout.setf(ios::showpos);
	cout.setf(ios::fixed,ios::floatfield);

	for(int i=1;i<=10;i++)
	{
		cout.setf(ios::internal, ios::adjustfield); 
		cout.width(5);
		cout<<i;
		cout.setf(ios::right, ios::adjustfield); 
		cout.width(20);
		cout<<sqrt(i)<<"\n";
	}
	cout.setf(ios::scientific, ios::floatfield);
	cout<<"\nSQRT(100)="<<sqrt(100)<<"\n"; 
	return 0;
}

Output:

value*******SQRT OF VALUE
+...1.............+1.0000
+...2.............+1.4142
+...3.............+1.7321
+...4.............+2.0000
+...5.............+2.2361
+...6.............+2.4495
+...7.............+2.6458
+...8.............+2.8284
+...9.............+3.0000
+..10.............+3.1623

SQRT(100)=+1.0000e+01

2. Manipulators

Manipulators are used to manipulate the output in specific format. Below is the list of manipulators in c++.

ManipulatorsUse
setw()To specify the required field size for displaying an output value.
setprecision()To specify the number of digits to be displayed after the decimal point of a float value.
setfill()To specify a character that is used to fill the unused portion of a field.
setiosflags()To specify format flags that can control the form of output display such as left or right justification.
resetiosflags()To clear the flags specified.

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