Questions regarding C++ Classes

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March 19th, 2002, 05:47 AM

Ratt

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Join Date: Mar 2002

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Questions regarding C++ Classes

Hi, teaching myself C++ and require some help / assistance.

Source Code 1

Code:

#include <iostream>
#include <iomanip>
using namespace std;

class Time;

// date class
class Date {
	int mo, da, yr;
public:
	Date(int m, int d, int y) {mo = m; da = d; yr = y;}
	friend void display(const Date&, const Time&); // bridge function
};

// time class
class Time{
	int hr, min, sec;
public:
	Time (int h, int m, int s) {hr = h; min = m; sec = s;}
	friend void display(const Date&, const Time&);	// bridge function
};

// a bridge friend function
void display(const Date& dt, const Time& tm)
{
	cout << dt.mo << '/' << dt.da << '/' << dt.yr;
	cout << ' ';
	cout << tm.hr << ':' << tm.min << ':' << setfill('0') << right << setw(2) << tm.sec;
}

int main()
{
	Date dt(2, 16, 97);
	Time tm(10, 55, 5);
	display(dt, tm);
	return 0;
}

1st Question:-
I've added the iomanip header and cout manipulators [ setfill('0') << right << setw(2) ] to the orignal source so that the display shows:
2/16/97 10:55:05 instead of 2/16/97 10:55:5

Is this an acceptable way of manipulating the data members or are there better alternatives?

Source Code 2

Code:

#include <iostream>
#include <cstring>
using namespace std;

// date class
class Date {
	int mo, da, yr;
	char *month;
public:
	Date(int m = 0, int d = 0, int y = 0);
	~Date();
         void display() const;
};

Date::Date(int m, int d, int y)
{
	static char *mos[] ={ "January", "February", "March", "April", "May", "June", 
                  "July", "August", "September", "October", "November", "December"};

        mo = m; da = d; yr = y;
            if (m !=0) {
		month = new char[strlen(mos[m-1])+1];
		strcpy(month, mos[m-1]);
                }
	    else
		    month = 0;
}

// destructor
Date::~Date()
{
    delete[] month;
}

// display member function
void Date::display() const
{
	if (month != 0)
		cout << month << ' ' << da << ", " << yr;
    	else
        	cout << da << ", " << yr;
}

int main()
{
	Date dt(5, 24, 2000);
	dt.display();
	return 0;
}

2nd Question:-
Referring to the Date function in the Date class, I can't understand the following assignment:

month = new char[strlen(mos[m-1])+1];

Since the following assignment will work just fine:

month = new char[strlen(mos[m-1])];

Are there any reasons to assign month the former way?

March 19th, 2002, 12:33 PM

M.Hirsch

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Posts: 5,966

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Reputation Power: 189

to your second question:

strings are terminated with a trailing \0. this is why you need to add one to the actual string length or it will start overwriting your next variable.
a single byte would do no harm on small programs since the 8 MSBs are anyway 0. but if you use a lot of memory or write drivers (or some other things probably too...) then it will kill the next variable on the heap when you strcpy() to it...

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