9.15.1. Time Example (Class Version)

The Time example consists of three files illustrating the organization of a larger, realistic program.

Time.h

contains the class specification. Programs realize several benefits by separating the class description from the function definitions:

• the class specification is easily and compactly included in documentation
• functions, which might embody trade secrets, are delivered to clients in machine code rather than full source code
• programs only have a single copy of the functions' machine code
• it's easier to build and manage client programs that use the class in some but not all of its files
• it's easier to reuse the class in other programs

Time.cpp

contains the member function definitions. Programs only need one copy of these functions. The linker joins the functions' machine code in this file with the calls made throughout the program.

driver.cpp

represents a client of the Time class. In a larger, more realistic program, the client code will typically span many files - some, but perhaps not all, of those files will use the services of a specific class.

The textbook introduced the Time program in chapter 4 as a structure example. We updated it in chapter 5 to demonstrate that structures can be passed to functions in three ways (a) by value, (b) by pointer, and (c) by reference. Parts of the Time class have been presented in the preceding sections of this chapter to illustrate various aspects of object-oriented programming. The following figures present the complete, final version of the program.

class Time
{
    private:
	int	hours;
	int	minutes;
	int	seconds;

    public:
		Time() : hours(0), minutes(0), seconds(0) {}
		Time(int h, int m, int s) : hours(h), minutes(m), seconds(s) {}
		Time(int s);

	Time	add(Time t2);

	void	print();
	void	read();
};

#include <iostream>
#include <iomanip>
#include "Time.h"
using namespace std;


Time::Time(int s)
{
	hours = s / 3600;
	s %= 3600;		// s = s % 3600;
	minutes = s / 60;
	seconds = s % 60;
}


void Time::print()
{
	cout.fill('0');
	cout << hours << ":" << setw(2) << minutes << ":" <<
		setw(2) << seconds << endl;
	cout.fill(' ');
}


Time Time::add(Time t2)
{
	int	i1 = hours * 3600 + minutes * 60 + seconds;
	int	i2 = t2.hours * 3600 + t2.minutes * 60 + t2.seconds;

	return Time(i1 + i2);
}


void Time::read()
{
	cout << "Please enter the hours: ";
	cin >> hours;

	cout << "Please enter the minutes: ";
	cin >> minutes;

	cout << "Please enter the seconds: ";
	cin >> seconds;
}

#include <iostream>
#include "Time.h"
using namespace std;


int main()
{
	Time	t;
	t.read();

	t.print();

	Time	s(1, 30, 4);
	s.print();

	Time	u = t.add(s);
	u.print();

	//t.add(s).print();	// alternate

	return 0;
}