IS this allowed in C++

Is the following acceptable ..

Code:

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#include <time.h>
#include <iostream>

class Date                                               
{
public:

        Date(Date& d); // THIS **

        // Give access to the object
        Date getDate() { return date; } // This is the reason I'm having the above

        void SetDate(tm curr_tm);
        static tm getCurrentTime();
        int getDay(){return day;}
        int getMonth(){return month;}
        int getYear(){return year;}
        int getHour(){return hour;}
        int getMinute(){return minute;}
        tm getLocalDT(){return local_dt;}
        friend std::istream& operator>>(std::istream& in, Date& date);
        friend std::ostream& operator<<(std::ostream& out, const Date& date);
       
private:

        int day;
        int month;
        int year;
        int hour;
        int minute;
        tm local_dt;

        Date &date; // THIS **
};


#endif;

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Looks a bit fishy. What could possibly be the purpose of the date member?

It doesn't look valid since you'll always need to have a valid instance of Date (or one of it's derived class) to initialize another instance. Which get to the question, how do you create the first instance of Date.

What you might want is to make getDate a static function. It would make more sense... I think. But then, what is getDate supposed to do ? And... what is this class supposed to be exactly ? The interface looks rather confused.

Quote:

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Originally Posted by anon

Looks a bit fishy. What could possibly be the purpose of the date member?

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I need to get the date (Day, Month, Year, Hour, Minute, Second) as one object ... There's a Class which has Date as a member .. need to initialize that member

Quote:

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Originally Posted by foxman

what is this class supposed to be exactly ? The interface looks rather confused.

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Date class like any other Date class .. What u mean is confused?

You basically have a chicken and the egg problem. In order to create a Date object you need to have an instance to an already existing Date object in which to assign the reference. However, in order to get that instance it would require an existing Date object in which to assign the reference. And the cycle continues.

I don't know if the compiler will spit out an error or not as it doesn't seem to be any syntax error, just a logic error.

Quote:

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Originally Posted by csonx_p

Date class like any other Date class .. What u mean is confused?

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I can understand the int members.

Then, in addition you have a tm member. What is that supposed to do, represent another date?

And finally, what is the purpose of the Date reference?

How many dates is one Date instance supposed to store?

Quote:

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Originally Posted by anon

Then, in addition you have a tm member. What is that supposed to do, represent another date?

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Yes, should this be a free function, or a friend maybe?

Looks fine as long as you add another constructor. Perhaps a default constructor that just initializes date to "*this". Though I'm not clear on what the purpose of getDate() is.

The only way to solve the chicken and egg problem caused by having a reference to the same type within the class (that I can see anyway) would be to have the constructor initialise it to *this. That would kind of defeat the purpose of having the reference since you could just use the 'this' pointer anyway.
I therefore conclude that it is an error to have a member of a class that is a reference to an object of that same class.

Aside from that, you seem to having problems choosing a style?

Date(Date& d); // THIS **
friend std::istream& operator>>(std::istream& in, Date& date);
friend std::ostream& operator<<(std::ostream& out, const Date& date);

Date &date; // THIS **

First it's Date& date, then it's Date &date.
A copy-n-paste error? An overlooked detail?
You should stick to one. And you've demonstrated you've used the former.

Quote:

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Originally Posted by Thantos

You basically have a chicken and the egg problem. In order to create a Date object you need to have an instance to an already existing Date object in which to assign the reference. However, in order to get that instance it would require an existing Date object in which to assign the reference.

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Not true. While I don't advocate the technique, a class X can contain a reference to X without relying on another instance existing. For example;

Code:

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class X
{
      public:

          X & const self;

          X() : self(*this) {};
};

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I've seen this sort of thing used by people who have migrated from other OO languages (smalltalk?) to C++, and are having trouble getting used to typing "*this" to say "self".

The problem with this is that it requires all constructors (copy constructors, etc) to be manually defined for every class ..... there can be absolutely no reliance on compiler-generated defaults.

Yes, I realise the problem in this thread is that a reference member is probably being used inappropriately. The above is noted in interests of completeness.

Code:

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Date getDate() { return date; } // This is the reason I'm having the above

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Why can't getDate do?

Code:

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Date getDate() { return *this; } // This is the reason I'm having the above

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--
Mats

Code:

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Date getDate() { return *this; } // This is the reason I'm having the above

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If this is really what the OP want, it would be quite ridiculous. That would be like

Code:

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int getInt(int n)
{
  return n;
}

int main()
{
  // a = 5 + 6
  int a = getInt(5) + getInt(6);
}

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...and I think we all agree that's useless, don't we ?

Quote:

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Originally Posted by foxman

Code:

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Date getDate() { return *this; } // This is the reason I'm having the above

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If this is really what the OP want, it would be quite ridiculous. That would be like

Code:

---

int getInt(int n)
{
  return n;
}

int main()
{
  // a = 5 + 6
  int a = getInt(5) + getInt(6);
}

---

...and I think we all agree that's useless, don't we ?

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And of course, the current convoluted way of doing the same thing is better?

In your example, it would be (somewhat simplified):

Code:

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int getInt(int n)
{
  int &nn = n;

  return nn;
}

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Edit: The above is obviously somewhat "Rube Goldberg"-esque. It serves no purpose, but it will work from a logical perspective. I could not think of the name "Rube Goldberg" when I wrote my post, but it was what I had in mind.

--
Mats

Quote:

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Originally Posted by grumpy

Code:

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          X & const self;

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That's not valid syntax. A reference cannot be const like that. The const key word must come before or after the X.