Topics
- The extraction operator takes two operands
- The
left operand is an input stream expression (like cin or an ofstream object)
- The
right operand is a variable to store input
Insertion Operator <<
- The insertion operator takes two operands
- The
left operand is an output stream expression (like cout or an ofstream object)
- The
right operand is an expression of a simple type, or a string, or a manipulator
Manipulators
- Manipulators are used only in input and output statements to control format
- Manipulators are found in both
<iostream> and <iomanip>
- Examples of manipulating text
- Allow for a “field width” to align text
- Change how values are displayed
Manipulators in <iostream>
-
endl: terminate the output line
-
fixed: display in decimal point format with 6 decimal places as default
-
showpoint: display a whole number in decimal format with 6 significant digits as default
Manipulators in <iomanip>
-
setw(n): fieldwidth specification manipulator
- Sets the width of the next value (int, float, string) to be printed over ‘n’ characters with right justification as default.
- This manipulator is the ONLY one that is NOT persistent. This means it only affects the very next item displayed.
- Useful to create/align columns in output.
-
setprecision(n): decimal number specification manipulator
- Sets ALL subsequent floating-point outputs to be displayed with ‘n’ decimal places of accuracy provided that fixed manipulator has already been specified.
- Default is 6 usually decimal places.
-
scientific: set ALL subsequent floating point output to be displayed in scientific notation. This is the default.
-
hex: set ALL subsequent output to be displayed in hexadecimal notation but will not place a ‘0x’ automatically in front of number.
-
dec: set ALL subsequent outputs to be displayed in decimal notation (base 10). Mainly used if you had previously set output to scientific or hex, and need to change back.
-
setfill(' '): fills the unused field width with the specified character. By default, this is a space. Useful for adding leading zeros.
-
left: set ALL subsequent outputs to left-justification within the printing field
-
right: set ALL subsequent outputs to right-justification within the printing field. This is the default, like Java’s .format().
setw() Quirks
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cout << left << setw(15) << "Hello" << " World\n";
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10 spaces (15 - 5) between Hello and World
This places Hello in a left justified field (starts on left side) with a MINIMUM 15 characters wide.
Since Hello is less than 15 characters, unused characters are filled with spaces by default.
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cout << right << setw(15) << "Hello" << " World\n";
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10 spaces (15 - 5) between Hello and World
This places Hello in a right justified field with a MINIMUM of 15 characters wide.
Again, unused characters are filled with spaces.
1
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cout << left << setw(3) << "Hello" << " World\n";
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If you exceed setw() width, nothing gets cut off. setw() is a MINIMUM, not a maximum.
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#include <iomanip>
#include <iostream>
using namespace std;
int main() {
double myNumber = 123.4;
double yourNumber = 3.14159;
cout << fixed << showpoint << setprecision(4);
cout << "Numbers are " << endl << setw(11) << myNumber << endl << setw(11) << yourNumber << endl;
return 0;
}
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- Each is displayed right justified and
-
Rounded if necessary and
- Located in a space of at least 11 positions and
-
4 places after the decimal point
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Numbers are
123.4000
3.1416
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Powerpoint
