Input And output (I/O) Stream Flags
To implement many of the above manipulators, I/O streams
have a flag field that specifies the current settings. The flag names and their
meanings are given below :
|
Flag Name
|
Meaning
|
|
skipws
right
internal
dec
oct
hex
showbase
showpoint
uppercase
showpos
scientific
fixed
unitbuf
stdio
|
skip white space during input
left justification of output
pad after sign or base indicator
decimal base (show integers in decimal
format)
octal base (show integers in octal format)
hexadecimal base (show integers in
hexadecimal format)
show base for octal and hexadecimal
numbers
show the decimal point for all floating
point numbers
show uppercase hex numbers
show ‘+’ to positive integers
use E for floating notation
use floating notation
flush all stream after insertions
flush stdout,stderr after insertion
|
Arguments for setflags
|
First Argument
(Flag Name)
|
Second Argument
|
|
ios : : skipws
|
|
|
ios : : left
ios : : right
ios : : internal
|
ios : : adjustfield
|
|
ios : : dec
ios : : oct
ios : : hex
|
ios : : basefield
|
|
ios : : showbase
ios : : showpos
ios : : uppercase
ios : : showpoint
|
|
|
ios : : scientific
ios : : fixed
|
ios : : floatfield
|
|
ios : : unitbuf
ios : : stdio
|
|
(a) Turning the bit format flag
on In order to change the state
of the cout object, the bits that represent its state must be
change. The staf ( ) function is invoked for
setting the bit format flags of the I/O stream.
The general
format of the setf ( ) function is,
cout.set(flags
to be set);
For example,
cout.staf(ios : : showbase) ;
The bitwise OR ( | )
operator is used in the argument list of the setf(
) function in
order to change the bit format flag more than one.
For example,
cout.setf
(ios : : showbase | ios : : showpoint | ios : : uppercase) ;
(b) Turning the bit flag off The
usetf ( )
function is used to change the bits directly off. This function takes
exactly one argument to turn off the bit pattern.
The general
syntax of the usetf ( ) function is,
Cout.unsetf(flags to be turned off);
For example,
cout.setf (ios : : showbase | ios : : showpoint |
ios : : uppercase) ;
(b) Turning the bit format flag off The usetf ( )
function is used to change the bits directly off. This function takes exactly
one argument to turn off the bit pattern.
The general syntax
of the unstf ( ) function is,
cout.unsetf( flags to be turned off);
For example,
cout.unsetf (ios : : uppercase) ;
The bitwise OR ( | ) operator is used in the argument list in order to turn
off more then one bit format flag of the I/O stream.
(c) Basefield bit format
flag The basefielde format flag
is used to display integers in the proper base.
ios : : dec show integers in decimal format
ios
: : oct show integers in octal format
ios
: : hex show
integers in hexadecimal format
Only one of the
above can be set at any time. These format flags control the base in which
numbers are displayed. By default, dec
is set. The syntax of the basefield bit format flag setting is
cout.setf (ios : : dec,ios : : basefield) ;
cout.setf (ios : : oct, ios : :
basefield) ;
cout.setf (ios : : hex, ios : : basefield)
;
PROGRAM 2.11
A program to display an integer number in different bases,
namely, dec, oct, and hex using the basefield format flag setting.
/ /using basefield bit format flag
#includ <iostream.h>
void main ( )
{
int num = 71 ;
cout << “ decimal = “
<<num << “\n”;
cout.setf (ios : : oct, ios : :
basefield);
cout << “ octal = “ << num
<< “\n”;
cout.setf (ios : : hex,ios : :
basefield);
cout << “ hexadecimal = “
<< num << “\n”;
cout.setf (ios : : dec, ios : :
basefield) ;
cout << “ decimal = “ <<
num << “\n”;
}
Output of the above
program
decimal
= 71
octal = 107
hexadecimal = 47
decimal = 71
(d) Showbase bit format flag The
showbase format flag is used to display the base for octal and hexadecimal
numbers. If showbase is set, this flag prefaces integral insertions with the
base indicators used with C++ constants. If hex is set, for instance, an OX will be inserted in front of any
integral insertion. This flag is not set by default. The unsetf ( ) function is invoked to undo the
base setting.
The syntax of the showbase flag is,
cout.setf( ios : : showbase);
PROGRAM
A program to display the base of the given integer numbers
using showbase flag.
/ /using showbase flag
#include <iostream.h>
void main ( )
{
int num = 71;
cout.setf (ios : : showbase);
cout << “ decimal = “ <<
num << “\n”;
cout.setf (ios : : oct, ios : : basefield);
cout << “ octal = “ << num
<< “\n”;
cout.setf (ios : : hex, ios : :
basefield);
cout << “ hexadecimal = “
<< num << “\n”;
cout.setf (ios : : dec, ios : :
basefield);
cout << “ decimal = “ <<
num << “\n”;
}
Output
of the above program
decimal = 71
octal = 0107
hexadecimal = 0x47
decimal = 71
(e) Showpos bit format flag The showpos
format flag is used to display the sign of an integer. If this flag is set, a
“+” sign will be inserted before any integral insertion. It remains unset by
default. Note that on positive decimal output, the ‘+’ is assumed, but by
default it will not appear. If the number is negative, the ‘-‘ sign will always
appear. The unsetf ( ) function is
invoked undo the setting of a positive sign.
The syntax of
the showpos flag is,
cout.setf(ios : : showpos);
PROGRAM
A program to show the sign of the given number using the showpos flag.
/ /using showpos flag
#include <iostream.h>
void main ( )
{
int num = 71;
cout.setf (ios : : showbase);
cout.setf (ios : : showpos);
cout << “ decimal = “ <<
num << “\n”;
cout.setf (ios : : oct, ios : :
basefield);
cout << “ octal = “ << num
<< “\n”;
cout.setf (ios : : hex, ios : :
basefield);
cout << “ hexadecimal = “
<< num << “\n”;
cout.setf (ios : : dec, ios : :
basefield);
cout << “ decimal = “ <<
num << “\n”;
}
Output of the above
program
decimal = +71
octal = 0107
hexadecimal = 0x47
decimal = +71
(f) Uppercase bit format flag The
uppercase bit format flag is used to display output in uppercase. By default,
The following notations always appear in lowercase.
- A hexadecimal number (a, b, c, d, e, f)
- The base of a hexadecimal number (0x)
- A floating point number in the scientific notation (0.3e3)
The unsetf ( ) function
is used to revert back to lowercase. The syntax of the uppercase format flag
is,
cout.setf (ios : : uppercase);
PROGRAM
A program to display the base of the given hexadecimal
number in uppercase using the flag setting.
/ /using showpos flag
#include <iostream.h>
void main ( )
{
int num = 0x2abc;
cout.setf( ios : : uppercase | ios :
: showbase);
cout << “ decimal = “ <<
num << “\n”;
cout.setf (ios : : oct, ios : :
basefield);
cout << “ octal = “ <<
num << “\n”;
cout.setf (ios : : hex, ios : :
basefield);
cout << “ hexadecimal = “
<< num << “\n”;
cout.setf (ios : : dec, ios : :
basefield);
cout << “ decimal = “ <<
num << “\n”;
}
Output of the above
program
decimal = 10940
octal = 025274
hexadecimal = 0X2ABC
decimal = 10940
(g) Formatting floating point
numbers The following sections
explain how floating values are formatted using the different flag setting in
C++.
PROGRAM
A program to show the floating point numbers without any
special formatting.
/
/using field justification
#include <iostream.h>
void main ( )
{
float a, b, c, d ;
a = 1.23456789 ;
b = 34.56 ;
c = 1.34E2 ;
d = -123.5677 ;
cout << “a = “ << a
<< “\n”;
cout << “b = “ << b <<
“\n”;
cout << “c = “ << c
<< “\n”;
cout << “d = “ << d
<< “\n”;
Output of the above
program
a
= 1.234568
b = 34.560001
c = 134
d = -123.567703
(h) Showpoint bit format
flag The showpoint bit format
flag is used to show the decimal point for all floating point values. By
default, the number of decimal position is six.
The syntax of
the showpoint flag is,
cout.setf( ios : : showpoint);
The unsetf (
) flag is invoked to undo the showing of all decimal values of a
floating point number.
PROGRAM
A program to display a floating point value with all decimal
place.
/ /using showpoint
#include <iostream.h>
void main ( )
{
float a, b, c, d ;
a = 1.23456789 ;
b = 34.56 ;
c = 1.34E2 ;
d = -123.5677 ;
cout.setf (ios : : showpoint);
cout << “a = “ << a
<< “\n”;
cout << “b = “ << b
<< “\n”;
cout << “c = “ << c
<< “\n”;
cout << “d = “ << d
<< “\n”;
}
Output of the above
program
a = 1.234568
b = 34.560001
c = 134.000000
d = -123.567703
(i) Precision The precision member function is
used to display the floating point value as defined by the user. The general
syntax of the precision
is,
cout.precision (int n)
where n
is number of decimal places of the floating value to be displayed.
For example,
cout.precision (5) ;
which display a floating point number
of five decimals.
PROGRAM
A program to display a floating point value in the formatted
from using the showpoint and precision member function.
/ /using showpoint and precision member
function
#include <iostream.h>
void main ( )
{
float a, b, c, d;
a = 1.23456789;
b = 34.560;
c = 134.000;
d = -123.568;
cout.stef(ios
: : showpoint) ;
cout.precision (3) ;
cout << “a = “ << a
<< “\n” ;
cout << “b = “ << b
<< “\n” ;
cout << “c = “ << c
<< “\n” ;
cout << “d = “ << d
<< “\n” ;
}
Output of the above
program
a = 1.235
b = 34.560
c = 134.000
d = -123.568
(j) Floatfield bit format
flag Sometimes a floating point
value may have to be displayed in scientific notation rather than in fixed
format.
(i) Scientific : When scientific is set, floating point values
are inserted using scientific notation. There is only one digit before the
decimal point followed by the specified number of precision digits which in
turn is followed by an uppercase or a lower case e
depending on the setting of uppercase and the exponent value.
The general syntax
of the scientific notation is,
Cout.setf( ios : : scientific, ios : :
adjustfield);
(ii) Fixed When
fixed is set, the value is inserted using decimal notation with the specified
number of precision digits following the decimal point. If neither scientific
nor fixed is set (the default), scientific notation will be used when the
exponent is less then 4 or greater than precision. Other wise, fixed notation
is used.
The general
syntax of the fixed notation is,
cout.setf(ios : : fixed, ios : :
adjustfield);
PROGRAM
A program to display a floating point value in both
scientific and fixed notation using the floating format flag.
/ /using fixed and scientific flag
#include <iostream.h>
void main ( )
{
float a, b, c, d ;
a = 1.23456789;
b = 34.56;
c
= 1.35E2;
d = -123.567 ;
cout.setf (ios : : showpoint) ;
cout.precision (3);
cout.setf (ios : : fixed, ios : :
floatfield) ;
cout << “ display in conventional
notation \n”;
cout << “a = “ << a <<
“\n” ;
cout << “b = “ << b << “\n”
;
cout << “c = “ << c <<
“\n” ;
cout << “d = “ << d <<
“\n” ;
cout.setf (ios : : scientific, ios : :
floatfield) ;
cout << “ display in scientific
notation \n”;
cout << “a = “ << a <<
“\n” ;
cout << “b = “ << b << “\n” ;
cout << “c = “ << c <<
“\n” ;
cout << “d = “ << d <<
“\n” ;
}
Output of the above
program
display
in conventional notation
a = 1.235
b = 34.560
c = 134.000
d = -123.568
display in scientific notation
a = 1.235e+00
b = 3.456e+01
c = 1.340e+02
d = -1.235e+02
(k) Adjustfield bit format flag
The adjust field consists of there field setting
ios :
: left left
justification
ios : : right right justification
ios : : internal pad
after sign or base indicator
(i) Left : Only one of these may be set at any time. If left is set, the inserted data will be flush
left in a field of characters width wide. The extra space, if any, will be
filled by the fill character (specified by the fill
function).
The general
syntax of the left justification
format flag is,
cout.setf(ios : : left ,ios : : adjustfield);
(ii) Right : If right is set, the inserted data
will be flush right.
The general
syntax of the right justification
format flag is,
cout.setf(ios::right,ios::adjustfield);
(iii) Internal : If
internal is set, the sign
of a numeric value will be flush left while the numeric value flush right, and
the area between them will contain the pad character.
The general syntax
of the internal
justification format flag is,
cout.setf(ios : : interal,ios : : adjustfield);
PROGRAM
A program to demonstrate how a field justification of an
integer value is carried out using the adjust field format flag.
/
/using field justification
#include <iostream.h>
void main ( )
{
int num = 71;
cour.fill ( ‘*’ );
cout.setf (ios : : showpos) ;
cout.setf (ios : : left, ios : :
adjustfield) ;
cout.width(6) ;
cout << num << “\n” ;
cout.setf (ios : : right, ios : :
adjustfield) ;
cout.width(6) ;
cout << num << “\n” ;
cout.setf (ios : : internal, ios : :
adjustfield) ;
cout << num << “\n” ;
cout.width(6) ;
}
Output of the above
program
+71***
***+71
+***71
(l) Fill and Width If the total number of characters
needed to display a field is less then the current field width, the extra
output spaces will be filled width the current fill character. In C++, it is
permitted to use any character to serve as the fill character. But by default
it is blank.
(i) Fill: The
fill ( ) member function is used to
specify a new fill character. Once it is specified, it remains as the fill
character unless it is changed.
The general syntax
of the fill ( ) member function is,
cout.fill(char ch);
Where ch
is a character to be filled.
For example,
cout.fill ( ‘*’ ) ;
cout.fill ( ‘0’ ) ;
(ii) Width : The
width ( ) member
function is used to specify the size of the data variable.
The general syntax of the width ( ) member function is,
cout.width(intn);
where n is a total field width of a
variable.
For example,
cout.width (10) ;
cout.width (3) ;
PROGRAM
A program to demonstrate how a fill and width member
function is used to display a numeral in C++.
/ /using fill and width
#includ <iostream.h>
void main ( )
{
cout.width (10) ;
cout.fill ( ‘x’ ) ;
int num = 6 ;
cout << num << “ \n” ;
cout.width (15) ;
cout.fill ( ‘b’ ) ;
num = 12345 ;
cout << num << endl ;
}
Output of the above
program
xxxxxxxxx6
bbbbbbbbbb12345
(m) Unitbuf When unitbuf is set, the stream is flushed
after every insertion. This flag is unset by default.
The general syntax
of the unitbuf is,
cout.setf(ios : : unitbuf);
/ /using unitbuf
#include <iostream.h>
void main ( )
{
cout.setf (ios : : unitbuf) ;
cout << “ this is a test program
to flush out \n” ;
cout << “ the input stream\n” ;
}
(n) Stdio This flag flushes the stdout and stderr
devices defined in stdio.h This is
unset by defult.
The general
syntax of the stdio flag is,
cout.setf(ios : : stdio);
/
/using stdio
#include <iostream.h>
void main ( )
{
cout.setf (ios : : stdio) ;
cout << “ this is a test program
to flush out \n” ;
cout << “ the input stream\n” ;
}
(o) Skipws If set, leading white space is
ignored on extraction. By default
skipws is set
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