How to initialize object in different class?

Question

I'm learning c++ and I have problem with basics. How to init object in different class?

For example I have code:

class A { private: static int num; static string val; public: A(int n, string w) { num = n; val = w; } };

I want to create object A in class B, so I have try like this:

class B { private: A objA; public: B(int numA, string valA){ objA = new A(numA, valA); } };

Different ways(same constructor):

 public: B(A obA){ objA = obA; }

or

 public: B(int numA, string valA){ objA = A(numA, valA); }

Always I'm getting error: No default constructor for exist for class "A". I've read that default constructor is constructor without any arguments, but I give them, so why it is searching default?

What's a LiczbaHeks? Read about constructor initializer lists. And it doesn't look like you want num and val to be static data members. — Praetorian
– Praetorian, Commented Apr 9, 2015 at 21:13
Yes, you need an initializer list. And don't use new like that. And, you could always add a default constructor, but in this case you shouldn't need it. — VoidStar
– VoidStar, Commented Apr 9, 2015 at 21:14
I edit that "LiczbaHeks". It is from my code, I haven't seen this. Sorry. — Ojmeny
– Ojmeny, Commented Apr 9, 2015 at 21:17

Emilio Garavaglia · Accepted Answer · 2015-04-09 21:27:41Z

If you want to learn C++ ... forget java. C++ variables are values, not pointers in reference disguise.

objA = new something is an abomination, since objA is A and not A*.

What you need is just explicitly construct objA with proper parameter

class B { private: A objA; public: B(int numA, string valA) :objA(numA, valA) { } } };

For more reference see http://en.cppreference.com/w/cpp/language/initializer_list

Thanks, it is a pity that I can't accept two answer. Vlad was first. Thanks any way!

Vlad from Moscow · Accepted Answer · 2015-04-09 21:19:49Z

2

You can do it the following way

class B { private: A objA; public: B(int numA, string valA) : objA( numA, valA ) {} };

answered Apr 9, 2015 at 21:19

Vlad from Moscow

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2 Comments

Ojmeny Over a year ago

Thanks! I can only say.. that c++ is strange :D

Vlad from Moscow Over a year ago

@Ojmeny Yes, it is not an intuitively clear language.

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