无法使用指向指针的指针的值获得相同的指针值？

Question

The program crash. I'm trying to implement a Brick ** create_bricks() function that return a pointer to pointer of Brick (because I want to create an array of Bricks and return the position of the first). I'm pulling my hair out and the last thing I do after several try and fails, erros and research, was to simplify my code and check value of the pointers line by line. When I dereference the_brick as *the_brick in the draw function game loop it doesn't get the same value as the one that new Brick() assign to ptr_brick inside create_bricks() function. I'm using SFML, but the problems is about pointers.

Note : If I return a Brick * from create_bricks with proper modifications it works fine (and draw the brick), but I need to create multiple bricks, no only one.

#include "Brick.h"

int main()
{
    ...

    while (window.isOpen())
    {
        Brick ** ptr_bricks = create_bricks();
        Brick * ptr_brick = *ptr_bricks;
        window.draw(*the_brick);
    }
    return 0;
}

Brick ** create_bricks()
{
    Brick * ptr_brick = new Brick();
    ptrBrick->setPosition(150, 20);
    return &ptrBrick;
}

#include "Brick.h"

Brick::Brick()
{
    LOG(INFO) << "Brick constructor";

    setPosition(10, 10);
    setSize(sf::Vector2f(100, 20));
    setFillColor(sf::Color::Green);
    setOutlineThickness(1);
}

Brick::~Brick()
{
    LOG(INFO) << "Brick destructor";
    //dtor
}

Thanks

Answer 1

The problem is the return statement in the create_bricks function:

return &ptrBrick;

Here you return a pointer to the local variable ptrBrick . The life-time of this variable will end when the function ends, and any pointer you have to it will become invalid as soon as the function ends.

The natural C++ solution to return an "array" from a function is to return a std::vector instead:

std::vector<Brick*> create_bricks()
{
    Brick* brick = new Brick;
    brick->setPosition(150, 20);
    return { brick };
}

If Brick is not a polymorphic class you don't even need to use a vector of pointer, but a vector of plain Brick objects ( std::vector<Brick> ).

If you persist in using pointers you must allocate an array of pointers to Brick , which means new Brick*[number_of_bricks] (or new Brick[number_of_bricks] if polymorphism isn't needed).