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Can we use a self referential class in C++? If yes what is the difference between self referencing in C and in C++
Is there any problems in storing the address of classes?
PS: I wrote a program using the concept in C++ but it isn't working. Reply asap
What do you mean by "self referential class"?
There is no such thing as the address of a class. A class is a category of object. Objects have addresses in memory. Categories do not.
Fine I meant the address of the objects!
So if you mean "can an object store its own address", then the answer is yes. In fact, you cannot stop an object from storing its own address, as that is what "this" represents.
I want to make the objects linked
Okay. There's not really anything stopping you from doing so. Use the & operator to get an address from an object.
If there's some error with the code you've written, you can get actual advice and hints if you tell us (a) what you did (i.e. show us what you've written) and (b) what errors you are getting.
Here is the code. The program is very simple, a book shop - in admin mode we need add books as in client mode we can subscribe them. I want to do this program using dynamic memory allocation not array of objects.
Code:/*Sarath*/
#include<iostream.h>
#include<conio.h>
class bookshop;
bookshop *start,*temp,*ptr;
class bookshop //self referential class to define a bookshop
{
char title[20]; //to store book title
char author[20]; //to store author name
float price; //price of the book
int copies; //no: of copies
public:
class bookshop *next; //to point to node of same class
public:
bookshop(bookshop *);
void admin(); //to enter new stock
void client(); //to search and purchase
void display(); //to display book details
};
bookshop::bookshop(bookshop *temp) //parametrised constructor
{ //to insert new node
if(start==NULL)
{
start=temp;
start->next=NULL;
}
else
{
ptr=start;
while(ptr->next!=NULL)
ptr=ptr->next;
ptr->next=temp;
temp->next=NULL;
}
}
void main()
{
int choice;
start=NULL;
clrscr();
do
{
cout<<"\n\n\tBook Shop\n";
cout<<"\n\t1. Admin\n\t2. Client\n\t3. Quit";
cout<<"\n\n\tChoice: ";
cin>>choice;
bookshop *temp=new bookshop(temp);
switch(choice)
{
case 1:
temp->admin();
break;
case 2:
temp->client();
delete temp; //to delete last node
break;
case 3:
cout<<"\n\tPress any key to quit..";
break;
default:
cout<<"\nInvalid choice!\n";
}
}while(choice!=3);
getch();
}
void bookshop::admin()
{
cout<<"\n\tBook title: ";
cin>>title;
cout<<"\n\tAuthor: ";
cin>>author;
cout<<"\n\tPrice: ";
cin>>price;
cout<<"\n\tNo of copiess: ";
cin>>copies;
display();
}
void bookshop::client()
{
start->display();
int flag=0;
cout<<"\n\tTitle?:";
cin>>title;
cout<<start;
ptr=start;
while(ptr->next!=NULL)
{
if(ptr->title==title)
{
ptr->display();
flag=1;
break;
}
ptr=ptr->next;
}
if(flag==0)
cout<<"\n\n\t"<<title<<" is not available!";
}
void bookshop::display()
{
cout<<"\n\n\t"<<title<<" is available";
cout<<"\n\tAuthor: "<<author;
cout<<"\n\tPrice: "<<price;
ptr=start;
while(ptr!=NULL) {
cout<<" "<<ptr->title; ptr=ptr->next;}
}
Your code is all over the place. Be careful with your global pointers, you are redeclaring local variables with the same name as your globals. Additionally:
1. void main is wrong. Read how to define main - FAQ
2. This is C++, not C. You should be using std::string vice char arrays.
3. Again since this is c++, you should be using std::vector vice trying to implement a linked list.
Letting us know what isn't working and the error messages you recieve is the way to get more specific help here.
Whats wrong in main? Linking is working well[I have checked by printing the addresses of the objects] But the problem is that I cant access the members using the object pointer.
No syntax errors. But when I print the values using "start->title" I am getting smileys and all :D
For a minute there I thought I was in the C forum section..
1) This isn't C++, it's "C with classes"
2) Replace your compiler with a standard-compliant one. iostream.h is pre-standard and deprecated.
3) Why are you rolling your own linked list? Use std::list
4) Why does each bookshop only hold one book? I suggest a single class bookshop which can hold several class book, in for example an std::list or vector
5) main is leaking memory. Look up RAII and smart pointers.
6) "bookshop *temp=new bookshop(temp);" temp is uninitialized when passed to bookshop()
I am not an expert in C/C++. Thats the answer for all the 'whys'. And thanks for the suggestions
I really appreciate pointing out mistakes, but whenever a newcomer is asking for help, everyone is proposing already-made tools. That's great, but keep in mind that C/C++ is used for learning BASIS of programming. The fact that you have smart pointers, linked-lists, vectors, strings here does not mean that these will be present in every other language. Telling him to use std::list to solve the problem is not the way to go. Let him get his idea working first and then prove it is not a good solution.
Yet you require from him distinguishing C from C++, while one is generally a superset of the other.
About the leaking memory:
The global pointer variable "start", which points to the first node, has to be deleted. The memory it points to has to be freed when it is no longer used. You might want to do this at the end of your main():
This will delete only the first node, since you pass to the delete operator only start. Nodes should be deleted recursively. You can do this implementing a destructor:Code:int main()
{
...
delete start; // we remove tree from memory
return 0;
}
Your constructor does not need the 'temp' parameter. You do not need to pass the object's address to any of its method, since it is done automatically by the language. Remove this parameter and use 'this' pointer instead, which has the functionality you want.Code:bookshop::~bookshop() // destructor
{
if(next!=NULL) // if this is not the last node, delete the next one
{
delete next;
}
}
I disagree. Computer science is not the only basis for programming; programmatic problem solving is another basis (now I feel like I'm talking linear algebra, but anyway...), and in this it makes sense to use the tools provided by C++. Sure, one should also learn how to implement these data structures, but this should be done as a separate exercise which comes with the teaching of how to utilise RAII. I suggest that you read Stroustrup's essay on Learning Standard C++ as a New Language (PDF) and Koenig and Moo's Accelerated C++ as an example of the general approach. (Sara th: you may want to consider working through Accelerated C++ yourself to get a good grounding in C++ and programming technique.)Quote:
Originally Posted by kmdv
@ sarath :
I I just read thcode. I think ur problem is that u can't search for a particular book. The mistake is , u have used == operator to compare strings.. Instead u should use strcmp()..
@others :
try to understand what is the problem he is facing.. And make him clarify it rather than confusing him with much complex things.
1. You can compare std::string objects with ==.Quote:
Originally Posted by krishnapollu
2. If you think using std::string is more complex than character arrays:
....either you are deliberately giving out wrong information.
....or more likely ...you use a prehistoric compiler and have never used strings.
_____
Also I think I agree with kmdv's post.
@Laserlight : Don't you think using a std::list would be a wrong thing to do ...for a student when he is learning about the implementation of a linked list ?
I also think that this was an assignment more or less connected with the implementation of a linked list.
To be more precise to my previous post: I do not encourage learning C++ by assigning C-style programs. BUT if someone has already faced a problem, wrote some code, he should be given an explanation of why it does not work, why it is a bad practise, and what is most important, run this code to see what happens. C/C++ is used for learning basic data structures, and it might have been this "separate assignment".
It isn't a language-specific approach, it even isn't thing-specific.
Thanks a lot Krishna! Error fixed and thank you all for the suggestions, especially kmdv.
By the way, this is not at all an implementation of linked list. An assignment, true, to implement a bookshop using class. I wanted to do it with dynamic memory allocation rather than going for an array of objects.
Why would a bookshop need to know the address of the next bookshop ? Your assignment (probably) means you to implement a bookshop by a linked list of books. If nothing is specified about the way you do it ...it would be much much easier to put the books into a std::list or std::vector...depending on how you want to access them .Quote:
Originally Posted by Sara th
Already said I am not an expert programmer. Means I don't know how to use std::list and all :D
That is my point. You DO NOT need to be an expert to use them. It is much simpler than making your own implementation and using it. Also it'd hardly take more than half an hour to learn the basic usage of those containers .
Oh come on! I was not aware of these things when I wrote the program. Next time I will try
i thnk ur prblm is us txt spk n frm.Quote:
Originally Posted by krishnapollu
These "complex things" you are referring to are standard C++ and are in fact easier to implement than a linked list or char arrays. If you do not know how to use the standard features of the language then maybe you should learn before contributing to this board. The answer was in fact provided, if the OP used std::string vice char arrays the use of '==' would have worked.Quote:
Originally Posted by krishnapollu
Well, let's see what the OP has to say about that......Quote:
Originally Posted by kmdv
So, since we are in fact using C++, then a solution using the STL with std::list and/or std::vector would be the solution. kmdv, we are in the business of teaching people how to program. This means to use the STL when appropriate and to properly implement the C++ language, which is not using char arrays or any other C feature such as the implementation of a user defined linked list.Quote:
Originally Posted by Sara th
Since you seemed to have missed the link Laser posted, here it is again: Learning C++ as a new language. Call me crazy but I think Bjarne Stroustrup might know what he is talking about when it comes to C++.
For your information, I am aware of the links other post.
I understand, I said:Quote:
This means to use the STL when appropriate and to properly implement the C++ language, which is not using char arrays or any other C feature such as the implementation of a user defined linked list.
The difference is that he has already started coding. If he hadn't and had asked "how can I implement a sequence of bookshops?" I would have answered "use std::list or std::vector". But he has shown his code and I attempted to point out his mistakes.Quote:
I do not encourage learning C++ by assigning C-style programs. BUT [...]
Yes. However, I also think that cluttering the learning of the implementation of a linked list with so many different member variables, and without any clarity in differentiating between a node and the entire linked list, is a wrong pedagogical approach.Quote:
Originally Posted by manasij7479
That's fine. You don't need to be aware of everything before you start.Quote:
Originally Posted by Sara th