Format Manipulators

 

Introduction	setiosflags	ios::left	scaling
setw	ios::showpoint	ios::right	Exercises
setprecision	ios::scientific	escape sequences

 

 

Introduction

 

C++ provides tools to format output.  These format manipulators are available by including the file <iomanip.h> as a compiler directive at the top of the source code.

 

#include <iostream.h>

#include <iomanip.h>

 

setw (width) manipulator

 

Causes the next value to be displayed in a field specified by width.  This setw (width) command is placed in the output expression prior to the output of variables or text constants. 

 

 

Code:

 

cout << setiosflags(ios::right);

 

cout << "1234567890" << endl;

cout << setw(10) << "abcde" << endl;

cout << 45 << endl;

 

Run output:

 

    1234567890

             abcde

    45

 

The text constant "abcde" will be right justified in a field-width of 10 columns.  However, the setw (10) does not affect the next output.

 

The setw (width) manipulator only applies to the next value to be printed.  However, the other manipulators will affect the appearance of all values which follow.

 

setprecision

 

controls the number of decimal points displayed by a floating point value.  The default precision display setting is 6 decimal places to the right of the decimal point. 

 

Code:

 

cout << 321.23456789 << endl;

        // default, prints 6 places to right of decimal

cout << setprecision (4);

cout << 321.2345678 << endl;          // displays 4 places to right of decimal

cout << 7.28 << endl;                       // only 7.28 gets printed, not enough places

cout << 25 << endl;                          // setprecision () has no effect on integers

 

Run output:

 

321.234568

321.2346

7.28

25

 

setiosflags manipulator

 

 

Provides for many options of which one or more can be used at a time.  Multiple options are separated by the (|) symbol.  Some of the options available are:

 

Option	Description
ios:showpoint	Displays decimal point and trailing zeros as necessary
ios::fixed	Displays real values in fixed-point form. Values are rounded off.
ios: scienfific	Displays real values in floating-point form
ios::left	Displays values left-justified
ios::right	Displays values right-justified within a field

 

Example 3: ios::showpoint

 

Code:

 

cout << setiosflags (ios::showpoint);       // will cause trailing zeros to print

cout << setprecision (4);

cout << 1.25 << endl;

 

Run output:

 

1.2500

 

Example 4: ios::scientific with setprecision ()

 

 

Code

 

cout << setprecision (2) << setiosflags (ios::scientific);

cout << 1.25 << endl;

cout << 12365.6219 << endl;         // answer is truncated to 2 decimal places

cout << 6.023e23 << endl;

 

Run output:

 

1.25e+00

1.23e+04

6.02e+23

 

Example 5: ios::left

 

 

Code:

 

cout << "12345678901234567890" << endl;

cout << setiosflags (ios::left) << setw (10) << "abcde";

//  left-justify state is still turned on

cout  << 45 << endl;

 

Run output:

 

12345678901234567890

abcde     45

 

Example 6: ios::right, ios::showpoint, ios::fixed, and setprecision()

 

 

Code:

 

cout << setiosflags (ios::right | ios::fixed | ios::showpoint);

cout << setprecision (2);

cout << setw(10) << 20 << endl;

cout << setw(10) << 25.95 << endl;

cout << setw(10) << 123.456 << endl;

 

Run output:

 

    20.00

    25.95

   123.46

 

Exercises

Exercise 1

Develop an 8 x 8 structure (no visible boundaries)

Place the character F around the perimeter.

Place the Character T in all other cells