EXC_BAD_ACCESS 仅在 function 内构建 object 时

Question

I'm working on a C++ project in XCode and I'm getting what appears to be some strange behavior (based on how I understand it). Here's my code:

#include <iostream>
#include <vector>
#include <string>

class beep {
public:
    virtual void greet() {
        std::cout << "bleep\n";
    }
};

class boop : public beep {
public:
    void greet() {
        std::cout << "bloop\n";
    }
};

class beep_master {
public:
    std::vector<beep*> beeps;

    void beep_everything() {
        for (int i = 0; i < beeps.size(); i++) {
            beeps[i]->greet();
        }
    }
};

beep_master factory() {
    boop boop1;
    boop boop2;

    beep_master master;
    master.beeps.push_back(&boop1);
    master.beeps.push_back(&boop2);

    return master;
}

int main(int argc, const char * argv[]) {
    beep_master master = factory();

    beep_master* ref = &master;

    ref->beep_everything();

    return 0;
}

I'm running this via XCode, and I'm getting an EXC_BAD_ACCESS in the for -loop in beep_master . Everywhere I've looked on the internet seems to indicate this is due to some memory management issues but I'm not really allocating anything dynamically.

I've noticed that if I move the contents of factory into main that I no longer get the error which leads me to believe it has something to do with boop1 and boop2 going out of scope and making the pointers invalid after the code exits that function.

Noodling on this, I'm beginning to think that this issue is unavoidable without the use of dynamic memory via the new operator and shared_ptr . Is this the right direction, or am I missing something in my setup here?

Answer 1

You are right. The factory function is storing pointers to local variables boop1 and boop2 which go away when the function returns, so you're left with pointers that point to invalid data.

You're pretty much going to have to dynamically allocate your objects to store the pointers in your vector.