CODEWITHSUNDEEP
c++constructorprivatefriend
user2907032
user2907032

Reputation: 467

Disallow private constructor invocation in friend function

Is there any way to not allow private construction in friend function, In case we do have private constructor with friend function in our class. Only Static method should be responsible for object creation and other than this compiler should flash error message

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

class a
{

public:
    void see ()
    {

    cout<<"Motimaa";

    }
    static a& getinstance()
    {
        static a instance;
        return instance;
    }

private:
    a() {};
    friend void access();
};
void access ()
{
a obj;
obj.see();//still friend function can access
}

int main()
{

a::getinstance().see();

access();
return 1;

}

Upvotes: 2

Views: 698

Answers (2)

Steven
Steven

Reputation: 2114

Friend functions can access all private members and variables, but there is a potential workaround for your problem, assuming you are trying to explicitly stop accidental use of the default constructor.

You could potentially make the default constructor kill the program. Now, create a second constructor that takes at least one argument, even if it's a meaningless argument.

Here's an example:

private:
  a() { cerr<<"Invalid call to constructor for object a!"; exit(); };
  a(bool dummyArg) {}

public:
  static a& getInstance() {
    static a instance(true);
    return a;
  }

Upvotes: 1

Vlad from Moscow
Vlad from Moscow

Reputation: 311058

friend functions have access to all members of the befriended class.

Upvotes: 0

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