Default constructor C++ error

Question

I require help with respect to class construction. In my class, I have used a copy constructor and operator= to prevent the compiler from creating them. In my main program, when I try to create an instance of the class, I get an error saying "No default constructor exists for the class".

What could be the problem?

This is a snippet of my code.

class netlist {
    netlist(const netlist &);
    netlist &operator=(const netlist &);
    std::map<std::string, net *> nets_;
}; // class netlist

In my main function I am using:

netlist nl;

This is where I get the error. I am providing the copy constructor declaration, so they should not be a problem.

I would appreciate any help with this. Thanks in advance.

Answer 1

There are two problems with the code -

1. class members are private by default.
2. "I get an error saying "No default constructor exists for the class" ".

Because if any kind of constructor is provided as a part of class declaration( netlist class has a copy constructor in this case), default constructor( i.e., constructor with no arguments ) is not provided by compiler.

netlist nl;  // And this invokes call to the default constructor and so
             // the error

---

netlist.h

class netlist {

public: // Added
    netlist(); // This just a declaration. Should provide the definition.
    netlist(const netlist &);
    netlist &operator=(const netlist &);
    std::map<std::string, net *> nets_;
}; // class netlist

netlist.cpp

netlist::netlist()
{
       // .....
}

// Other definitions

Answer 2

When you create the netlist you are not passing any arguments to the constructor which means you are calling a default constructor. However you didn't define a default constructor. You only created a constructor taking a different netlist as a parameter (the copy constructor) here:

netlist(const netlist &);

You should define a default constructor like this:

netlist();

Note that had you not defined any constructor, the compiler would have added default ones but since you added the copy constructor, you have to define all of them yourself.