Features for formatting output

C++ provides three groups of features to format output:

1. ios class member functions
2. ios format flags (with setf() / unsetf())
3. Manipulators (<iomanip> and <iostream>)

1. ios member functions

• width(n) – minimum field width, applies to the next item only.
• precision(n) – number of significant digits (decimals with fixed).
• fill(c) – padding character for unused field width.
• setf(), unsetf() – set/clear flags.

cout.width(8); cout.fill('#'); cout << 42;      // ######42
cout.precision(3); cout << 3.14159;             // 3.14

2. Format flags

• Justification: ios::left, ios::right, ios::internal
• Base: ios::dec, ios::oct, ios::hex, with ios::showbase
• Floating point: ios::fixed, ios::scientific, ios::showpoint
• Others: ios::showpos, ios::uppercase, ios::boolalpha

cout.setf(ios::showpos);
cout.setf(ios::fixed, ios::floatfield);
cout.precision(2);
cout << 7.5;                                    // +7.50
cout.setf(ios::hex, ios::basefield);
cout << 255;                                    // ff

3. Manipulators

• setw(n), setfill(c), setprecision(n), setiosflags(f), resetiosflags(f)
• endl, ends, flush, dec, oct, hex, left, right, fixed, scientific

cout << setw(10) << setfill('*') << left << "Hi" << endl;   // Hi********
cout << hex << 255 << dec << " " << 255 << endl;             // ff 255

Complete example

#include <iostream>
#include <iomanip>
using namespace std;
int main() {
    cout << left  << setw(10) << "Item"
         << right << setw(8)  << "Price" << endl;
    cout << left  << setw(10) << "Book"
         << right << setw(8)  << fixed << setprecision(2) << 250.5 << endl;
    cout << left  << setw(10) << "Pen"
         << right << setw(8)  << 15.0 << endl;
    return 0;
}

Output:

Item         Price
Book        250.50
Pen          15.00

Difference in use

• width() and setw() affect only the next value; the others stay until changed.
• Manipulators can be chained inside one cout statement; ios functions need separate statements.