Several Data Types

The I/O Manipulators

In addition to setting or clearing the format flags directly, you can alter the format parameters of a stream through the use of special functions called manipulators, which can be included in an I/O expression. The standard manipulators are shown in the following table:

Manipulator	Purpose	Input/Output
boolalpha	Turns on boolapha flag	Input/Output
dec	Turns on dec flag	Input/Ouput
endl	Output a newline character and flush the stream	Output
ends	Output a null	Output
fixed	Turns on fixed flag	Output
flush	Flush a stream	Output
hex	Turns on hex flag	Input/Output
internal	Turns on internal flag	Output
left	Turns on left flag	Output
nobooalpha	Turns off boolalpha flag	Input/Output
noshowbase	Turns off showbase flag	Output
noshowpoint	Turns off showpoint flag	Output
noshowpos	Turns off showpos flag	Output
noskipws	Turns off skipws flag	Input
nounitbuf	Turns off unitbuf flag	Output
nouppercase	Turns off uppercase flag	Output
oct	Turns on oct flag	Input/Output
resetiosflags(fmtflags f)	Turn off the flags specified in f	Input/Output
right	Turns on right flag	Output
scientific	Turns on scientific flag	Output
setbase(int base)	Set the number base to base	Input/Output
setfill(int ch)	Set the fill character to ch	Output
setiosflags(fmtflags f)	Turn on the flags specified in f	Input/Output
setprecision (int p)	Set the number of digits of precision	Output
setw(int w)	Set the field width to w	Output
showbase	Turns on showbase flag	Output
showpoint	Turns on showpoint flag	Output
showpos	Turns on showpos flag	Output
skipws	Turns on skipws flag	Input
unitbuf	Turns on unitbuf flag	Output
uppercase	Turns on uppercase flag	Output
ws	Skip leading whitespace	Input

To use a manipulator that takes a parameter, you must include <iomanip>.

Programming Tip 

One of the most interesting format flags found in the modern iostream library is boolalpha. This flag can be set either directly of by using the manipulators boolalpha() of noboolalpha(). What makes boolalpha so interesting is that setting it allows you to input and output Boolean values using the keywords true and false. Normally, you must enter 1 for true and zero for false. For example, consider the following program:

// Demonstrate boolalpha format flag. #include <iostream> using namespace std; int main () {   bool b;   cout << "Before setting boolalpha flag: ";   b = true;   cout << b << " ";   b = false;   cout << b << endl;   cout << "After setting boolapha flag: ";   b = true;   cout << boolalpha << b << " ";   b = false;   cout << b << endl;   cout << "Enter a Boolean value: ";   cin >> boolalpha >> b;   cout << "You entered " << b;   return 0; } 

Here is a sample ren:

Before setting boolalpha flag: 1 0 After setting boolalpha flag: true false Enter a Boolean value: true You entered true

Once the boolalpha flag has been set, Boolean values are input and output using the words true or false. As the program shows you must set boolalpha flag for cin and cout separately. Like all format flags, setting boolalpha for one stream does not imply that it is also set for another.