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Summary
37) Stream Manipulations
38) Manipulators
39) Non Parameterized Manipulators
40) Parameterized Manipulators
41) Format State Slags
42) Formatting Manipulation
43) Showing the Base
44) Scientific representation
45) Exercise
Stream Manipulations
After having a thorough look into the properties and object definition of I/O streams,
we
will discuss their manipulations. Here, there is need of some header files to include
in our
program the way, cin
and cout
are used. We include
iostream.h and
fstream.h while
using
file manipulations. In case of manipulation of the I/O streams, the header file
with the
name of iomanip.h
is included.
It is required to be included whenever there is need of
employing manipulators.
As discussed earlier, we can determine the state of a stream. The states of the
stream can
be determined. For example, in case of
cin, we can check where
the end of file comes.
For state- checking, these stream objects have set of flags inside them. These flags
can be
considered as an integer or long integer. The bit position of these integers specifies
some
specific state. There is a bit for the end of file to test. It can be written as
under:
cin.eof() ;
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It will return the state of end of file. The bit will be set if the file comes to
an end.
Similarly, there is a fail
bit. This bit determines whether an operation has failed or not.
For example, an operation could be failed due to a formatting error. The statement
cin.fail; will return the value of the
fail bit. As this statement
returns a value, we can use
it in an ‘if statement’ and can recover the error. Then there is a
bad bit.
This bit states that
data has lost. The presence of this bit means that some data has lost during I/O
operation.
So we can check it in the following manner.
cin.bad();
It can be used in parentheses as a function call that will allow us to check whether
the
operation failed or successful. Similarly we can also check for’
good’, that is a bit
showing that everything is good. This bit will be set if
fail and
bad bits are not set. We
can check this bit as cin.good
; and can find out whether the input operation was
successful. If some bit like
bad has been set, there should also be a mechanism to clear it.
For this, we have
cin.clear() ;
as a member function for these objects. This will reset the bits to their normal
good state.
This is a part of checking input stream.
Manipulators
Whenever carrying out some formatting, we will want that the streams can manipulate
and a number should be displayed in a particular format. We have stream manipulators
for doing this. The manipulators are like something that can be inserted into stream,
effecting a change in the behavior. For example, if we have a floating point number,
say
pi (л), and have written it as
float pi = 3.1415926 ;
Mow there is need of printing the
value of pi up to two decimal places i.e. 3.14 . This is a formatting functionality.
For this,
we have a manipulator
that tells about width and number of decimal points of a number
being printed. Some manipulators are parameter less. We simply use the name of the
manipulator that works. For example, we have been using
endl, which is actually
a
manipulator, not data. When we write
cout << endl ; a new line
is output besides
flushing the buffer. Actually, it manipulates the output stream. Similarly
flush was a
manipulator for which we could write
cout << flush that means
flushing the output
buffer. So it manipulates the output.
A second type of manipulators takes some argument. It can be described with the
help of
an example. Suppose we want to print the value of pi up to two decimal places. For
this
purpose, there should be some method so that we can provide the number i.e. two
(2) up
to which we want the decimal places. This is sent as a parameter in the manipulators.
Thus we have the parameterized manipulators.
Let’s have a look on what streams do for us. We know that streams are like ordered
sequence of bytes and connect two things i.e., a source and a destination. In the
middle,
the stream does some conversion. So it may take some binary representation of some
information and convert it into human readable characters. It may also take characters
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and convert them into an internal representation of data. With in the conversion
of data,
we can do some other things. For example, you might have seen that if a system prints
computerized cheques, it puts some special characters with the numbers. If there
is a
cheque for four thousand rupees, this amount would be written on it as ****4000.00.
The
idea of printing * before the amount is that no body could insert some number before
the
actual amount to change it. As we don’t want that somebody has increased the amount
on
the cheque from Rs 4000 to Rs 14000.The printing of * before the amount is a
manipulation that we can do with input or output objects. We can also tell the width
for a
number to be printed. So there are many conversions that we can do. We can use fill
characters like * as mentioned in the example of cheque printing. To accomplish
all these
tasks, there are different methods. So it becomes a little confusing that the same
work is
being done through 2-3 different methods. Some are inline manipulators like
endl. We
can use it with <<
and write inline as
cout << endl ; The same work could be done with
the flush method.
We could also write cout.flush
; Thus it is confusing that there is an
inline manipulator and a function for the same work.
Non-Parameterized Manipulators
Let’s start with simple manipulators. We have been dealing with numbers like integers,
floats etc for input and out put. We know that our number representations are associated
with some base. In daily life, the numbers of base 10 are used in arithmetic. When
we see
4000 written on a cheque, we understand that it is four thousands written in the
decimal
number system (base 10). But in the computer world, many systems are used for number
representation that includes binary (base 2), octal (base 8), decimal (base 10)
and
hexadecimal (base 16) systems. A simple justification for the use of these different
systems is that computers internally run on bits and bytes. A byte consists of eight
bits.
Now if we look at the values that can be in eight bits. 256 values (from 0 to 255
) can be
stored in eight bits. Now consider four bits and think what is the highest number
that we
can store in four bits. We know that the highest value in a particular number of
bits can
be determined by the formula 2n - 1 (where n is the number of bits).
So the highest value
that can be stored in four bits will be 24 - 1 i.e. 15. Thus the highest
value, we can store in
four bits is 15 but the number of different values that can be stored will be 2n
i.e. 16
including zero. Thus we see that while taking half of a byte i.e. four bits, 16
(which is the
base of hexadecimal system) different numbers can be stored in these four bits.
It means
that there is some relationship between the numbers that have a base of some power
of
two. So they can easily be manipulated as bit format. Thus four bits are hex. What
about
eight (octal)? If we have three bits, then it is 23 = 8, which is
the base of octal system.
Thus, we can use three bits for octal arithmetic.
We can use manipulators to convert these numbers from one base to the other. The
manipulators used for this purpose, can be used with
cin and
cout. These are nonparameterized
manipulators. So if we say the things like
int i = 10 ; Here
i has the
decimal value 10. We write
cout << i ; and 10 is being displayed on the screen. If we
want to display it in octal form, we can use a manipulator here. If we write
cout << oct << i ;
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it will display the octal value of i (10) which is 12. This manipulator converts
the
decimal number into an octal number before displaying it. So the octal representation
of
10 which is 12, will be displayed on the screen. Similarly if we write
cout << hex << i ;
Here hex stands for the hexadecimal.
hex is the manipulator
that goes into the out put
stream before i
and manipulates the stream by converting the decimal number into a
hexadecimal number. As a result, the hexadecimal value of 10 is displayed on the
screen.
If we have a number in octal or hexadecimal system , it can be converted into a
decimal
number by putting the dec
manipulator in the stream like
cout << dec << i ;
These (oct, hex and dec) are very simple inline manipulators without any argument.
There is also a manipulator for white space. The white space has a special meaning.
It is a
delimiter that separates two numbers (or words). In
cin and
cout, the white space acts
as a
delimiter. If we want that it should not act as a delimiter, it can used as a
ws manipulator.
This manipulators skips white space. This manipulator takes no argument. This
ws
manipulator is sometime useful but not all the times. The following table shows
the nonparameterized
manipulators and their description.
Manipulator Domain Effect
dec In / Out Use decimal conversion base
hex In / Out Use hexadecimal conversion base
oct In / Out Use octal conversion base
endl Output Inserts a new line and flush the stream
ends Output Terminate a string with NULL
flush Output Flush the stream
ws Input Skip leading whitespace for the next
string extraction only
The base becomes important while doing programming of scientific programs. We may
want that there is the hexadecimal presentation of a number. We have discussed the
justification of using hexadecimal or octal numbers, which is that they match with
bits.
Here is another justification for it. Nowadays, computers are just like a box with
a button
in front of them. A reset button is also included with the main power button. While
seeing
the pictures or in actual Miniframe and mainframe computers, you will notice that
there
is a row of switches in front of them. So there are many switches in front of these
computers that we manipulate. These switches are normally setting directly the values
of
registers inside the computer. So you can set the value of register as 101011 etc
by
switching on and off the switches. We can do that to start a computer or signaling
something to computer and so on. There are a lot of switches in front of those computers
ranging between 8 to 16. You have to simply remember what is the value to start
the
computer. Similarly, it will require the reading the combinations of switches from
the
paper to turn on the computer. This combination tells you which switch should be
on and
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which should be off. As a human being instead of remembering the whole pattern like
10110000111 etc, it could be easy to remember it as 7FF. Here we are dealing with
HEX
numbers. For the digit 7, we need four bits. In other words, there is need to set
four
switches. The pattern of 7 is 0111. So we set 7 with this combination. For F, all
the four
bits should be on as 1111 and so on. Thinking octal and hexadecimals straight away
maps
to the bits. It takes a little bit of practice to effectively map on the switches.
On the other
hand, decimal does not map to those bits. What will be its octal number in case
of
decimal number 52.? You have to calculate this. What is the binary representation
of 52?
Again you have to calculate. There are a lot of things which you have to calculate.
On the
hand, if we say 7ABC in case of HEX, we are mapping the number straight away on
four
bits. In octal system, we map the number on three bits. A is ten so it will be 1010
so you
can quickly set the switches. It may not be relevant today. But when you are working
with big computers, it will become quite relevant. There are many times when we
have to
manipulate binary data using mechanical device while thinking in hexadecimal and
octal
terms. In the language, you have the facility to set the base. You can use
setbase(),
hex,
oct, dec and setf.
There are many ways of doing the same thing. Programmers write these
languages. Therefore they make this facility available in the language as built
in.
Parameterized Manipulators
Suppose we want to print the number 10 within a particular width. Normally the numbers
are written right justified. In case of no action on our part,
cout displays a number
left
justified and in the space required by the number. If we want that all numbers should
be
displayed within the same particular width, then the space for the larger number
has to be
used. Let’s say this number is of four digits. Now we want that there should be
such a
manipulator in the output that prints every number in a space of four digits. We
have a
manipulator setw
(a short for set width), it takes as an argument the width in number of
spaces. So to print our numbers in four spaces we write
cout << setw(4) << number ;
When printed, this number gets a space of four digits. And this will be printed
in that
space with right justification. By employing this mechanism, we can print values
in a
column (one value below the other) very neat and clean.
Now in the example of printing a cheque, we want that the empty space should be
filled
with some character. This is required to stop somebody to manipulate the printed
figure.
To fill the empty space, there is need of manipulator
setfill. We can write this
manipulator with cout
as the following
cout << setfill (character) ;
where the character
is a single character written in single quotes. Usually, in cheque
printing, the character * is used to fill the empty spaces. We can use any character
for
example, 0 or x. The filling character has significance only if we have used
setw
manipulator. Suppose, we are going to print a cheque with amount in 10 spaces. If
the
amount is not of 10 digits, the empty space will be filled with *. Thus the usage
of setfill
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is there where we use setw
for printing a number in a specific width. So if we want to
print an amount in 10 spaces and want to fill the empty spaces with *, it can be
written as
under.
cout << setfill(*) << setw(10) << amount ;
Thus the manipulators can also be of cascading nature. The stream insertion operator
(<<) is overloaded and every overload of it returns a reference to the
cout object itself.
This means that while working from left to right, first the fill character will
be set
returning a reference to cout
. Later, its width will be set to 10 character and return a
reference to cout again.
Finally, the amount will be displayed in the required format.
Thus, we have manipulated the stream in two ways. Example of a pipe with two bends
can help it understand further. Now whatever figure goes into it, its width and
the fill
character is set and things are displayed in the space of 10 characters. If we want
to print
an amount of Rs 4000 on the cheque, it will be printed on the cheque as ******4000.
Thus, we have two manipulators,
setw and
setfill which are used
with cout.
Let’s further discuss the same example of cheque. In real world, if we look at a
computer
printed cheque , the amount is printed with a decimal point like 4000.00 even if
there is
no digit after decimal point. We never see any amount like 4000.123, as all the
currencies
have two- digit fractional part. Thus, we examine that the fractional part has been
restricted to two decimal places. The decimal digits can be restricted to any number.
We
have a manipulator for this purpose. The manipulator used for this purpose is
setprecision. This is a parameterized manipulator. It takes an integer
number as an
argument and restrict the precision to that number. If we write
cout << setprecision (2) << float number ;
The above statement will display the given float number with two decimal places.
If we
have the value of pi stored in a variable, say
pi, of type float with
a value of 3.1415926
and want to print this value with two decimal places. Here, manipulator
setprecision can
be used. It can be written as under.
cout << setprecision (2) << pi ;
This will print the value of
pi with two decimal places.
Now think about it and write on the discussion board that whether the value of pi
is
rounded or truncated when we print it with setprecision manipulator. What will be
the
value of pi with five decimal places and with four decimal places? Will the last
digit be
rounded or the remaining numbers will be truncated?
At this point, we may come across some confusion. We have learned the inline
manipulators that are parameter less. For these, we simply write
cout << hex <<
number; which displays the number in hexadecimal form. There is also
a parameterized
manipulator that performs the same task. This manipulator is
setbase. It takes the base
of
the system (base, to which we want to format the number) as an argument. Instead
of
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using oct, dec and
hex manipulators,
we can use the setbase
manipulator with the
respective base as an argument. So instead of writing
cout << oct << number ;
we can write
cout << setbase (8) << number ;
The above two statements are equivalent in the way for having the same results.
It is a
matter of style used by one of these manipulators. We can use either one of these,
producing a similar effect. The
cout << setbase(8) means
the next number will be printed
in the base 8. Similarly cout
<< setbase(16) means the next number will be printed in
hexadecimal (base 16) form. Here a point to note is that
setbase (0) is the same
as
setbase(10).
Following is the table, in which the parameterized manipulators with their effect
are
listed.
Manipulator Domain Effect
resetioflags(long
f)
In / Out Clear flags specified in f
setbase (int b) In / Out Set numeric conversion base to b (b may be 0, 8, 10 or
16)
setfill (int c) Output Set fill character to c
setiosflags(long f) In / Out St flags specified in f
setprecision (int
p)
Output Set floating point precision to p
setw (int w) Output Set field width to w
Format State Flags
We have discussed that there are flags with the stream objects. This set of flags
is used to
determine the state of the stream. The set includes
good, fail, eof etc that
tells the state of
the stream. There is also another set of flags comprising the ones for input/output
system
(ios). We can use setioflag,
and give it as an argument a
long number. Different
bit values
are set in this number and the flags are set according to this. These flags are
known as
format state flags and are shown in the following table. These flags can be controlled
by
the flags,
setf and
unsetf member functions.
Format state flag Description
ios::skipws Skip whitespace character on an input stream.
ios::left Left justify output in a field, padding characters appear to the right
if necessary.
ios::right Right justify output in a field, padding characters appear to the left
if necessary.
ios::internal Indicate that a number’s sign should be left justified in a field
and
a number’s magnitude should be right justified in that same field
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(i.e. padding characters appear between the sign and the number).
ios::dec Specify that integers should be treated as decimal (base 10) values.
ios::oct Specify that integers should be treated as octal (base 8) values.
ios::hex Specify that integers should be treated as hexadecimal (base 16)
values.
ios::showbase Specify that the base of a number is to be output ahead of the
number(a leading 0 for octals, a leading 0x or 0X for
hexadecimals).
ios::showpoint Specify that floating-point numbers should be output with a
decimal point. This is normally used with ios::fixed.
ios::uppercase Specify that uppercase letters (i.e X and A through F) should be
used in the hexadecimal integers and the uppercase E in scientific
notation.
ios::showpos Specify that positive and negative numbers should be preceded by
a + or - sign, respectively.
ios::scientific Specify output of a floating-point value in scientific notation.
ios::fixed Specify output of a floating-point value in fixed point notation
with a specific number of digits to the right of the decimal point.
Let’s talk about more complicated things. We discussed a parameterized manipulator
setw that sets the width to print in the output. There is an alternative
for it i.e. the member
function, called ‘width()’.
This function also takes the same parameter and an integer, in
which width the things are to display or read. This function applies to both input
and
output stream. For this, we write
cin.width (7). This will
create a format field of the width
of 7 characters for an input. Now we write
cout.width (10) ; this
will set the width of
output field to 10. With it, the next number to be printed will be printed in 10
spaces.
Thus setw, inline
manipulator has the alternative function
cin.width and
cout.width with
single argument.
It equally applies to the setprecision.
This is the parameterized, inline- manipulator that
sets the places after the decimal point. There is a member function as well in these
objects that is precision.
The setprecision
is an inline manipulator, used along with
stream insertion (<<). If we want to do the same thing with a function call,
cout.precision(2) is written. It has the same effect as that of
cout << setprecision (2).
Thus we have different ways of doing things.
We have used setfill
manipulator. Here is another member- function i.e.
cout.fill. The
behavior of this function is exactly the same. We simply write
cout.fill(‘*’) ; identical
to
cout << setfill(‘*’). The filling character is mostly used whenever we
use financial
transactions but not necessarily. We can also use zero to fill the space.
So fill and
setfill,
width and
setw,
precision and
setprecision and almost
for every inline
manipulator, there are member functions that can be called with these streams.
The member functions are defined in
iostream.h. However, the
manipulators are defined
in iomanip.h. Normally
we have been including iostream.h
in our programs to utilize the
member functions easily. But inclusion of a header file ‘iomanip.h file is must
for the use
of manipulators.
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We should keep in mind that when we can write inline manipulators in the following
fashion.
cout << setw (7) << i ;
And in the next line we write
cout << j ;
Here the setw manipulator
will apply to i
only and not after that to
j. This means that
inline manipulators apply only to the very next piece of data i.e. output. It does
not apply
to subsequent output operations.
Formatting Manipulation
We can adjust the output to left side, right side or in the center. For this purpose,
we have
a member function of the object whose syntax is as under:
cout.setf(ios:: flag,
ios:: adjust field)
The setf is a short
for set flag. The flags are long integers, also the part of the objects.
They are the bit positions, representing something. Here we can set these flags.
The flags
of adjustfield are
set with values i.e. left, right, left | right and internal. The description of
these is as follows.
Value of flag Meaning Description
left Left-justify
output
Justifies the output to left side
right Right-justify
output
Justifies the output to right side
left | right Center output Centralized the output
internal Insert padding Places padding between signs or base indicator
and the first digit of a number. This applies only
to number values and not to character array.
Following is the code of a program that shows the effects of these manipulators.
//This program demonstrate the justified output
#include <iomanip.h>
#include <iostream.h>
void main()
{
int i = -1234;
cout.setf(ios::left, ios::adjustfield);
cout << "|" << setw(12) << i << "|" << endl;
cout.setf(ios::right, ios::adjustfield);
cout << "|" << setw(12) << i << "|" << endl;
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cout.setf(ios::internal, ios::adjustfield);
cout << "|" << setw(12) << i << "|" << endl;
cout.setf(ios::left | ios::right,
ios::adjustfield);
cout << "|" << setw(12) << i << "|" << endl;
cin >> i ;
}
Following is the output of the above program.
|-1234 |
| -1234|
|- 1234|
| -1234|
We have discussed two types of manipulators for base, the parameter less manipulator
in
which we look for oct,
dec and
hex. On the other hand,
there is a parameterized
manipulator setbase
which takes an integer to set the base. It uses 0 or 10 for decimal, 8
for octal and 16 for hexadecimal notations.
Now we have a generic function
setf that sets the flags.
We can write something like
cout.setf(ios::hex)
The hex is defined in ios.
It has the same effect. It sets the output stream, in this case
cout, to use hexadecimal display for integers. So it is the third way
to accomplish the
same task. The use of these ways is a matter of programming style.
Showing the base
Now there should be someway to know which base has the number output by the
programmer. Suppose we have a number 7ABC, then it be nothing but hexadecimal.
What will be the nature of 7FF. It is hexadecimal. However, the number 77 (seven
seven)
is a valid number in all of different basis. We have a built-in facility
showbase. It is a
flag. We can set the showbase
for output stream that will manipulate the number before
displaying it. If you have the
showbase falg on (by default
it is off), a number will be
displayed with special notations. The
setf function is used to
set the flag for the base field.
Its syntax is as under:
cout.setf(ios::base,
ios::basefield);
Here base has three values i.e. oct, dec and hex for octal, decimal and hexadecimal
systems respectively. If the basefield is set to
oct (octal), it will display
the number with a
preceding zero. It shows that the number is in octal base. If the basefield is set
to hex
(hexadecimal), the number will be displayed with a preceding notation 0x. The number
will be displayed as such if the basefield is set to
dec (decimal). If there
is a number, say
77, it will be difficult to say that it is in octal, decimal or hexadecimal base,
a valid
number for all the three systems. However, if we output it with the use of
showbase, it
will be easy to understand in which base the output number is being represented.
The
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following example, demonstrates this by showing the number (77) along with the base
notation.
/* This program demonstrate the use of show base.
It displays a number in hex, oct and decimal form.
*/
#include <iostream.h>
void main()
{
int x = 77;
cout.setf(ios::showbase);
cout.setf(ios::oct,ios::basefield); //base is 8
cout << x << '\n'; //displays number with octal notation
cout.setf(ios::hex,ios::basefield); //base is 16
cout << x << '\n'; //displays number with hexadecimal notation
cout.setf(ios::dec,ios::basefield);
cout << x << '\n';
}
Following is the output of the program.
0115
0x4d
77
Scientific Representation
When the numbers get bigger, it becomes difficult to write and read in digits format.
For
example, one million will be written as 1000000. Similarly hundred million will
be
100000000 (one with eight zeros). How will we display the number which is of 20-digit
long? For this, we use scientific notation. To do it, a manipulator
ios:: scientific can be
used. If the flag in setf
to the scientific
is set, it can be written as
cout.setf(ios::scientific, ios::floatfield) ;
Then the floating point numbers will be displayed in scientific notation. A number
in
scientific is like 1.946000e+009. So we can set the state of output stream to use
scientific
notation for outputting a number.
To do the scientific notation off and restore the default notation, we set the flag
in setf
function to fixed
(which is a short for fixed point notation). This can be written as
cout.setf(ios::fixed, ios::floatfield) ;
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Uppercase/Lowercase Control
Similarly, we have a manipulator
ios::uppercase. While using
this manipulator, the e in
scientific notation is written in uppercase i.e. E. If we are using hexadecimal
numbers,
then the characters of it will be displayed in uppercase letters as A, B, C, D,
E and F.
Exercise
• We have been using matrices i.e. a two dimensional array. As an exercise,
try to
print out a matrix of three rows and three columns, in such a way that it should
be
nicely formatted. The numbers should be aligned as we write it in a neat and clean
way on the paper. You can use the symbol | at the start and end of each row as we
don’t have a so big square bracket to put around three rows. To be more elegant
to
print a matrix, we can use a proper graphic symbol to put square brackets around
the matrix instead of using | symbol. In the ASCII table, there are many symbols
that we can use to print in our programs. We have the integer values of these
symbols in the table. Suppose you have a value 135 of a symbol. Now to print this
symbol, press the ‘alt’ key and keeping the key pressed enter the integer value
i.e.
135 from the num pad of the key board, release the ‘alt’ key. Now you will see
that symbol on the screen. For the value 135, the symbol is ç. In programming, we
can provide this symbol to be printed as a single character in single quotes. For
this, put a single quote and then enter the symbol in the way stated above and then
put the single quote. It will be written as ‘ç’. Find out proper symbols from the
ASCII table that can comprise to put a square bracket around the matrix.
• Write simple programs to demonstrate the use of different manipulators
and
examine their effects. |
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