unable to make default constructor for class with reference as member variable

[chnnaveen]

I facing some issue in below code
...

 class Temp {
                private :
                        string &s ;
                        int index;
                public :
                        Temp():index(0) {}   
                       Temp(string &Ls) :s(Ls),index(0){}
                       Temp& Temp::operator=(const Temp&){
				   this->s =Temp.s;
				   this ->index = Lst.index;
				   return *this ;
			}
	};

while compiling I’m getting the error message as

error: uninitialized reference member `temp::s'

In the main function call I can able to declare as

Temp it("test");

but I want declare like this

Temp it ;

can anyone suggest some other way to sort out this problem.

[guestgulkan]

You need to initialise reference memebers in the initialisation list - they cannot be left unitialised (as you have found).

So:
1. Do without a default constructor - (could be a problem in certain circumstances);

2. Don't have reference members.

[chnnaveen]

But iterator will have the reference to the container but we can able to declare the iterator without assign to any container

string::iterator it;

in this case how reference object should initialized since above will call zero argument on constructor.

[guestgulkan]

You are confused about something.

Iterators are classes and they are defined as a nested class of the type they iterate on.

Something along this (very) general lines

class string
{
     public:
      class string_random_iterateor
      {
           
       };

      typedef string_random_iterator iterator;
};

So you can say string::iterator it; //created a string iterator variable

iterators behave like pointers NOT references

They are several good books on the STL out there if you are interested in further reading.


So in your class - I would say - get rid of that parameter as a reference and just have string s

[chnnaveen]

It’s ok I explain my entire program....
I’m creating a container type class contain the array of string and a iterator class to access it.

my header files as below :-

//string.h
#include <string>
#include <iostream>
using namespace std;

class Lstring {
        private :
                string s[100];
                int count;
        public :
                Lstring();
                Lstring( const Lstring&);
                ~Lstring();

                const char* operator [] (int i)const ;
                int push_back(const string );
                void print()const;


        //class iterator;
        //friend class iterator ;
        class iterator {
                private :
                        Lstring &s ;
                        int index;
                public :
                        //iterator();
                        iterator(Lstring &);
                        iterator(Lstring&,bool);
                        iterator& iterator::operator=(const iterator&);
                        ~iterator();
                        iterator& operator ++(int );
                        friend ostream& operator<<(ostream& os, const iterator& it);



        };
                        iterator  begin();
                        iterator  end() ;
};

and main function is

//main.cpp
int main()
{
        Lstring Lst;
        Lst.push_back("Test1");
        Lst.push_back("Test2");
        Lst.print();
        Lstring L2 = Lst;
        L2.print();
//		Lstring::iterator it
        Lstring::iterator it =  Lst.begin();
        cout << endl << " in the Begin Iterator"<<it<<endl;
        it++;
        cout << endl << " in the Incrementing Iterator"<<it<<endl;
        it = Lst.end();
        cout << endl << " in the End Iterator"<<it <<endl;
        return 0;
}

i have wrttien this program with refernce to the thinking in cpp volume 1 (chapter Introduction to Templates - page 764) book.

here if want to declare the iterator alone without assiging to the any container(Lstring) class. then how i have to code the zero argument constructor of iterator class.

if pointer are used for references how iterator class implementated to access the container oject.

[guestgulkan]

But you will notice that the book does not attempt to have a default constructor.

So they don't do IntStackIter it; as you are trying to do - they doIntStackIter it(is); - they realise the problem.

If you want to have a default constructor then use pointers instead of references.

[chnnaveen]

thanks.. for suggestion ...

In that program i have a question i.e use of declaring the iterator class as friend.

friend class iterator ;

[guestgulkan]

The StackInt class has some private variables:

class IntStack {
enum { ssize = 100 };
int stack[ssize];
int top;

The iterator needs access to these private variables:

// 
class IntStackIter {
IntStack& s;
int index;
public:
IntStackIter(IntStack& is) : s(is), index(0) {}
int operator++() { // Prefix
require(index < s.top,//<<=====Iterator class accesses private member of StackInt class
"iterator moved out of range");
return s.stack[++index]; //<<===== and here
}
int operator++(int) { // Postfix
require(index < s.top, //<<===== and here
"iterator moved out of range");
return s.stack[index++];//<<===== and here
}
};

So the StackInt class declares the IntStackIter iterator class to be a friend - to allow it to access the private members.