Formatted I/O

Formatted I/O

•  In this section we will learn how to control the information flow. There is a set of format flags that control the way information is formatted. The ios class declares the values that are used to set or clear the format flags ‒

• Following are the format flags along with their meaning.

Flags : Meaning

Skipws: If this flag is set then leading white spaces are discarded (skipped). On clearing this flag the leading white spaces are not discarded.

left: On setting this flag the output becomes left justified.

right: On setting this flag the output becomes right justified.

internal: If it is set then numeric value is padded to fill the field between any sign or base character  and number.

oct: It is set means numeric values are outputted in octal.

dec: It is set means numeric values are outputted in decimal.

hex: It is set means numeric values are outputted in hex.

showbase: If set then it shows base indicator(for example 0X for hex).

showpos: It shows+ sign before positive numbers.

showpoint: On set it shows decimal point and trailing zeros for all floating point numbers.

Scientific: On set it shows exponential format on floating point numbers.

 fixed: On set it shows fixed format on floating point numbers.

boolalpha: Booleans can be set using true or false.

uppercase: On setting this flag upper case A‒F are used for hex values and E for scientific values.

• The oct, dec and hex fields are collectively referred as basefield. The left, right and internal fields can be referred as adjustfield, similarly scientific and fixed can be referred as floatfield.

• The setf() function is used to set the flag and unsetf() function is used to clear the flag.

• For example, if we want the text to be displayed on the console should be right justified then ‒

cout.setf(ios::right);

cout<<"Twinkle Twinkle Little Stars";

Following is a program that shows how several format flags can be used.

#include <iostream>

using namespace std;

int main()

{

    cout << 100.75 << "hello India" << 100 << "\n";

    tortuot cout << 10 << " " << ‒10 << "\n";

    cout << 100.0 << "\n\n";

    cout.unsetf(ios::dec);

    cout.setf(ios::hex| ios::scientific);

    cout << 100.75 << "hello India<< 100 << "\n";

    cout.setf(ios::showpos);

    cout << 10 << " " << ‒10 << "\n";

    cout.setf(ios::showpoint | ios::fixed);

    cout << 100.0;

    retrun 0;

}

Output

100.75 hello India 100

10‒10

100

1.0075e+02 hello India 64

a fffffff6

+100.000000

width(), precision() and fill()

There are three important member functions that define the fields like width, precision and fill characters.

•  By default the output value contains the number of characters as per the space occupied by it. But we can define the width of the output by using width() function.

For example

cout.width(10);

cout<<"ABCD"

•  It will set minimum field width of 10. That means in a line total number of bobo characters are 10. In above cout statement the text "ABCD" contains 4 characters only. Hence first 6 blank characters and then ABCD will be printed on the output screen. The output will be

ABCD

That means we get the right justified output.

•  Following program illustrates the use of width, precision and fill functions.

#include<iostream>

using namespace std;

int main()

{

cout << "ABCD "<<"\n";

cout.width(10);

cout<<"ABCD "<<"\n"; //sets right justified text

cout.fill('*'); // set fill character

cout.width(10); // set width

cout<<"ABCD"<<"\n";

// right justified text with preceding *hence the total number of characters are 10

cout.setf(ios::left); // left justify

cout.width(10); // set width

cout<<"ABCD"<<"\n"; // output left justified

cout.width(10); // set width

cout.precision(10); //set 10 digits of precision

cout << 10.203040 << "\n";

indacout.precision(4); // set 4 digits of precision

cout << 102.0304050 << "\n";

cout.width(10);

cout.fill('*');

cout <<""; //simply prints * 10 times

return 0;

}

Output

ABCD

ABCD

******ABCD

ABCD******

10.20304**

102.0304

**********