C++ multiple constructor with different arguments

Question

I have one ABC class whose constructor is taking 3 arguments e.g x1, x2 and l. One sample code is shown below. I am trying to make another constructor in the same class ABC that should take different arguments but, I am unable to do. It might be a very general question but I am unable to get satisfactory answers.

     class ABC {
      protected:
      X1& _x1;
      X2& _x2;
      Logger& _logger;
      ABC(X1& x1, X2& x2, Logger& l):_x1(x1), _x2(x2),_logger(l) {}
      ABC(X1& x1, Logger& l):_x1(x1),_logger(l) {} //getting error uninitialized reference member ‘ABC::_x2’
      ~ABC(){this->clear();}
      void clear(){}
      };

error uninitialized reference member ‘ABC::_x2'

You are missing an initializer of reference _x2. If the reference to X2 is optional maybe you should use a pointer to the X2 object or set _x2 to a static instance of X2. — Lukas Thomsen
– Lukas Thomsen, Commented May 25, 2015 at 20:18

banach-space · Accepted Answer · 2015-05-25 19:47:02Z

1

The compiler is telling you the truth - you need to initialize the second reference in your class, i.e. _x2.

You cannot have uninitialized references so either don't use them or you need to initialize them in every constructor that you declare.

answered May 25, 2015 at 19:47

banach-space

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2 Comments

musafir Over a year ago

Okay, does it means that there is no way to make 2nd constructor for the above example ?

banach-space Over a year ago

If you insist on _x2 being a reference then you need to initialise it in the second constructor. Otherwise don't declare it as a reference. Look at dasblinkenlight's answer.

Dietmar Kühl · Accepted Answer · 2015-05-25 19:49:27Z

1

Well, thecompiler tells you what the problem is (and it is inrelated to having multiple constructors): your class has a reference member which is not initialized in the constructor: _x2. All reference members need to be initialized in the constructor.

answered May 25, 2015 at 19:49

Dietmar Kühl

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Comments

Sergey Kalinichenko · Accepted Answer · 2015-05-25 19:50:04Z

1

C++ requires you to initialize all reference members. If there are situations when a reference to an object is optional, it's best to replace a reference variable with a pointer:

X2* _x2;

If you must have a reference with a default, make a private static variable for it, and use that variable to initialize your reference variable:

class ABC {
private:
    static X2 _x2_default; // Declare it in a CPP file
protected:
    ...
    ABC(X1& x1, Logger& l):_x1(x1),_logger(l), _x2(_x2_default) {}
    ...
};

answered May 25, 2015 at 19:50

Sergey Kalinichenko

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2 Comments

musafir Over a year ago

I think this is the answer I am searching for. Thank you.

Sergey Kalinichenko Over a year ago

@musafir You are welcome! Try this out and see if the approach works for you. If it does, please consider accepting the answer by clicking the grey check mark next to it. This would let others know that your problem is solved, and earn you a new badge on Stack Overflow.

Werner Erasmus · Accepted Answer · 2015-05-25 20:06:49Z

0

A reference must be initialised. For class members, this means initialisation in the member initializer list of the constructor.

If the member may be remain uninitialized, make it a pointer and ensure that it is default initialized (ie :m2_() //null, where m2_ is M2* m2_;), or wrap it with a smart pointer that at least ensures default initialization

edited May 25, 2015 at 20:06

answered May 25, 2015 at 19:50

Werner Erasmus

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