Question

I’m to extend a C++ class, but have absolutely no background in that language. Googling didn’t help me understand how to solve the compilation error:

Constructor for 'JRB2World' must explicitly initialize the base class 'b2World' which does not have a default constructor

So, there is this b2World.h

class b2World
{
public:
    b2World(const b2Vec2& gravity);
    ~b2World();

    // ...

And its .cpp:

b2World::b2World(const b2Vec2& gravity)
{
    // ...
}

b2World::~b2World()
{
    // ...
}

My class header:

#import "Box2D.h"

class JRB2World : public b2World {

    float factor;

public:

    JRB2World(const b2Vec2& gravity);
    ~JRB2World();

    float getFactor();
    void setFactor(float f);
};

My class implementation:

JRB2World::JRB2World(const b2Vec2& gravity) {

// Constructor for 'JRB2World' must explicitly initialize the base class 'b2World' which does not have a default constructor
}

JRB2World::~JRB2World() {
}

float JRB2World::getFactor(){

    return factor;
}

void JRB2World::setFactor(float f){

    factor = f;
}

I suppose it has to do with a call to the “super constructor” like in java or objc. How can this be done?

Answer 1

Just put the constructor into the initializer list of the inherited class’ constructor:

JRB2World::JRB2World(const b2Vec2& gravity) : b2World(gravity) {
}

Depending on what you want to do, I wouldn’t use inheritance here: Put the Box2D world into a member variable. That should make it easier to replace it, just in case its interfaces changes over Versions or you decide to use another physics engine later on.