Q:

Box2D world size

I have created a box2d world, and I wanted to limit the height of the world. 
I did search google and apparently there was an option in the previous version of box2d where you would have to define the size of your world, but I am not sure if you were able set the height of the world but in the current version they have taken that option completely off. 
So I am just looking for a way to limit the height, as my player is a ball that jumps up and down and I want to limit how high it can jump (the jumps are done by physics and gravity and the speed of the ball so after a few good jumps, the ball jumps really high as its speed increases and I dont want to limit the speed) and put border on let say y=900.

A:

The Box2D world has an infinite size. You can't limit the world, but you can create a shape that encloses a certain area in the Box2D world.
Here's how to create a body and shape that puts a shape just around the screen, so that objects don't leave the screen. It is easy to adapt this code by changing the corner coordinates to fit whatever you need:
        // for the screenBorder body we'll need these values
        CGSize screenSize = [CCDirector sharedDirector].winSize;
        float widthInMeters = screenSize.width / PTM_RATIO;
        float heightInMeters = screenSize.height / PTM_RATIO;
        b2Vec2 lowerLeftCorner = b2Vec2(0, 0);
        b2Vec2 lowerRightCorner = b2Vec2(widthInMeters, 0);
        b2Vec2 upperLeftCorner = b2Vec2(0, heightInMeters);
        b2Vec2 upperRightCorner = b2Vec2(widthInMeters, heightInMeters);

        // static container body, with the collisions at screen borders
        b2BodyDef screenBorderDef;
        screenBorderDef.position.Set(0, 0);
        b2Body* screenBorderBody = world->CreateBody(&screenBorderDef);
        b2EdgeShape screenBorderShape;

        // Create fixtures for the four borders (the border shape is re-used)
        screenBorderShape.Set(lowerLeftCorner, lowerRightCorner);
        screenBorderBody->CreateFixture(&screenBorderShape, 0);
        screenBorderShape.Set(lowerRightCorner, upperRightCorner);
        screenBorderBody->CreateFixture(&screenBorderShape, 0);
        screenBorderShape.Set(upperRightCorner, upperLeftCorner);
        screenBorderBody->CreateFixture(&screenBorderShape, 0);
        screenBorderShape.Set(upperLeftCorner, lowerLeftCorner);
        screenBorderBody->CreateFixture(&screenBorderShape, 0);

Note: this code is for Box2D v2.2.1. I assume that's what you're using because you said "previous version" which required this code to be written differently (with the SetAsEdge method).

