Implicitly-deleted constructor error

beginners
#1

hello,

i am facing a problem which is more a C++ problem.

Call to implicitly-deleted default constructor of 'ofApp'

seems like a default constructor issue but i can’t figure it out as i am not a C++ expert

I have 3 classes :

  • base ofApp
    no custom constructor

  • Creature class
    custom constructor with parameters
    Creature::Creature(ofPoint _pos, int size, ofColor _color)

  • Branch class (of which a Creature is made of)
    custom constructor with parameters
    Branch::Branch(float _length, float _startAngle)

    // Branch
    class Branch {
    public :
    Branch(float _length, float _startAngle);
    };

//

//Creature
class Creature {
public:
    Creature(ofPoint _pos, int size, ofColor _color);        
    vector<Branch> branches;
};

//

//ofApp.h
class ofApp : public ofBaseApp{
	public:
		void setup();
		void update();
		void draw();
    Creature creature;
};

//ofApp.cpp
void ofApp::setup(){
    creature = Creature(pos, 65, col);
}

Any clue ?

thanks

1 Like
#2

Hi there,

I will try my best to explain wht i think its going on here. You might want to listen to more experienced people though.

So you are creating a class Creature that can be created only if you provide 3 arguments (pos, size, color). Then in ofApp you want tot create an instance to it without providing any argument:

Creature creature;

This is contradictory and the compiler complains.
There are several solutions here.

The first one (not recommended) is to turn that instance into a pointer. so it becomes:

	Creature* creature;

and then in setup you can create the object with new:

creature = new Creature(ofPoint(2,2), 65, ofColor::red);

which means that you will have to delete it at some point, which could lead to difficulties.

The second solution I suggest, i think is cleaner and better, just allow the creation of the class without arguments with a constructor with no arguments, and much better if you give a default value to those parameters (pos, size, color)

Creature() {
	pos = ofPoint();
	size = 0;
	color = ofColor();
};

Then you can instantiate the class as before, without pointers.

#3

Hi,
check this
http://en.cppreference.com/w/cpp/language/default_constructor
towards the end of this reference you’ll find an example and you’ll understand why it is not working for you.

hope this helps.

#4

Hello,

thanks a lot for your answers and links.

i also found this links which is quite good.

There are some tips like using an empty default constructor or forward declaration. I kind of get the general idea but it is quite still fuzzy to me.

So i tried the C++11 way

//Creature
class Creature {
public:
    Creature() = default;
    Creature(ofPoint _pos, int size, ofColor _color);
    vector<Branch> branches;
};

and it works.

But what is bugging me here is i am creating a default constructor for Creature, but this class includes a vector of Branch objects which also don’t have a default constructor but it works without complaining…

#5

because you are not creating any branch automatically only when pushing them into the vector where you use the constructor with parameters

#6

OK. I thought if i create a vector of 10 branches, this would create 10 instances of Branch like Branch branch would do…

#7

yes, resize for example shouldn’t work but as long as the vector is empty and you push the elements one by one the default constructor is not being used

#8

Ok, i get it.
One more thing learned :wink:
Thanks a lot and have a nice day.