Constructor not called c++

Question

I have this code in a DLL:

Game::Game(int width, int height)
   : world(width, height),
     renderer("Game", 800, 600),
     font(),
     text(),
     keyboard()
{
    // Code
}

keyboard is a pointer to a Keyboard object. The code inside the constructor is called, but the keyboard object remains null. Why is the object not being created?

The keyboard constructor:

Keyboard() {
 A = new Key('a');
 B = new Key('b');
 C = new Key('c');
 D = new Key('d');
 E = new Key('e');
 F = new Key('f');
 G = new Key('g');
 H = new Key('h');
 I = new Key('i');
 J = new Key('j');
 K = new Key('k');
 L = new Key('l');
 M = new Key('m');
 N = new Key('n');
 O = new Key('o');
 P = new Key('p');
 Q = new Key('q');
 R = new Key('r');
 S = new Key('s');
 T = new Key('t');
 U = new Key('u');
 V = new Key('v');
 W = new Key('w');
 X = new Key('x');
 Y = new Key('y');
 Z = new Key('z');

 ZERO = new Key('0');
 ONE = new Key('1');
 TWO = new Key('2');
 THREE = new Key('3');
 FOUR = new Key('4');
 FIVE = new Key('5');
 SIX = new Key('6');
 SEVEN = new Key('7');
 EIGHT = new Key('8');
 NINE = new Key('9');

 ARROW_UP = new Key(' ');
 ARROW_DOWN = new Key(' ');
 ARROW_LEFT = new Key(' ');
 ARROW_RIGHT = new Key(' ');

 SHIFT = new Key(' ');
}

How do I cause the keyboard constructor to be called?

If `keyboard` is a pointer, you're gonna need to allocate memory for it, else it will remain `NULL` — AndyG, Mar 24 '14 at 19:59
new to c++? perhaps you should catch up on the basics first ... — Walter, Mar 24 '14 at 20:04

score 6 · Accepted Answer · edited May 23 '17 at 12:20

if keyboard is a pointer the syntax should be

Game::Game(int width, int height)
  : world(width, height),
    renderer("Game", 800, 600),
    keyboard(new Keyboard)
{ ... }

The same also should be done for text/font if they're also pointers.

I don't want to offend you, but this is a quite basic question about how pointers/instances work in C++. If you're learning C++ by writing and trying code before reading about the language then please consider investing some time on reading first instead.

The reason is that C++ is an horrible language to learn by experimentation for two main reasons:

Not everything is logical. Much of C++ rules are a consequence of the evolution of the language and of committee decisions. The most obvious answer to a problem is often NOT the correct one in C++. The only way to know the language is to read about it.
The language main philosophy is that programmers never make mistakes. In other languages when you make a mistake a "runtime error angel" stops the program and tells you what went wrong. In C++ instead when you make a mistake an "undefined behavior daemon" takes the legal ownership of the code and will try hard to cause you the most possible damage, for example by making the program running anyway silently and nicely for a while until you decide to show it to someone, and only crashing it at that point.

The mix 1 + 2 is very dangerous: the language is complex and you will not be told about mistakes. Do yourself a favor instead and read first a good C++ book cover to cover.

And it would be even better if OP didn't use raw pointers at all for ownership of dynamically allocated memory, but a *smart pointer* like `std::unique_ptr`. — Felix Glas, Mar 24 '14 at 20:03
The object that allocates the memory to store the object is also usually a good place to free the memory for the object when it goes out of scope. If you follow this answer, you should delete the keyboard in the destructor. And since you have a bunch of new calls in your keyboard (hopefully your keyboard destructor will delete those. — johnb003, Mar 24 '14 at 21:00

Constructor not called c++

1 Answers1