Dereferencing a null point when using malloc()?

[bluerose1]

Essentially, I am trying to use malloc here but the green line is letting me know I am dereferencing a null pointer here? It seems like a simple error but I don't understand why it is happening.

For context wall is a simple struct, that is a member of the PortalPanic class that looks like this:

class PortalPanic : public MinigameBase
{
public:
struct wall {
int xCord;
int yCord;
int width;
sf::Color color;
sf::RectangleShape wallRect;
};
.
.
.
more class stuff

 

[mmorais]

I am not using c++, but it is working for me...

 

[codingd]

I received assistance from generative AI to understand the issue I was facing with dereferencing a null pointer when using malloc to allocate memory for your wall structure. The AI explained that if malloc fails to allocate the requested memory, it returns a null pointer, and attempting to access any members of that null pointer leads to undefined behavior. It emphasized the importance of checking whether the pointer returned by malloc (or calloc) is nullptr before using it, which is a crucial step in preventing errors.

#include <iostream>
#include <cstdlib> // Pour malloc et free

class PortalPanic {
public:
    struct wall {
        int xCord;
        int yCord;
        int width;
        // Supposons que nous n'utilisons pas de couleur ou de forme ici pour simplifier
    };

    wall* createWall(int x, int y, int width) {
        // Allocation de mémoire pour un nouveau mur
        wall* newWall = (wall*)malloc(sizeof(wall));
        if (newWall == nullptr) {
            std::cerr << "Erreur d'allocation de mémoire pour wall." << std::endl;
            return nullptr; // Gestion de l'erreur
        }

        // Initialisation des membres de la structure
        newWall->xCord = x;
        newWall->yCord = y;
        newWall->width = width;

        return newWall; // Retourne le pointeur vers le nouveau mur
    }

    void destroyWall(wall* w) {
        if (w != nullptr) {
            free(w); // Libération de la mémoire
        }
    }
};

int main() {
    PortalPanic game;
    PortalPanic::wall* myWall = game.createWall(10, 20, 30);

    if (myWall != nullptr) {
        std::cout << "Mur créé avec succès : "
                  << "xCord = " << myWall->xCord
                  << ", yCord = " << myWall->yCord
                  << ", width = " << myWall->width << std::endl;

        // Libération de la mémoire
        game.destroyWall(myWall);
    }

    return 0;
}