Is this some sort of pointer error? - c++

Question

I'm working on a small game in my free time and while coding it I came across an issue.
I've isolated the issue and made it as small as possible here:
#include <iostream>
#include <memory>
#include <vector>
#include <Windows.h>
class Base
{
public:
std::string p;
virtual ~Base()
{
}
virtual std::vector<std::shared_ptr<std::string>> getText() = 0;
};
class Derived1 : public Base
{
public:
Derived1()
{
p = "from1";
}
std::vector<std::shared_ptr<std::string>> getText()
{
return std::vector<std::shared_ptr<std::string>>{std::shared_ptr<std::string>(&p)};
}
};
class Derived2 : public Base
{
public:
Derived2()
{
p = "from2";
}
std::vector<std::shared_ptr<std::string>> getText()
{
return std::vector<std::shared_ptr<std::string>>{std::shared_ptr<std::string>(&p)};
}
};
int main()
{
std::unique_ptr<Base> state;
std::vector<std::shared_ptr<std::string>> displayText;
state.reset(new Derived1());
displayText = state->getText();
while(1)
{
for(auto i = displayText.begin(); i != displayText.end(); ++i)
std::cout << **i;
if (GetKeyState('2') < 0)
{
state.reset(new Derived2());
displayText.clear();
displayText = state->getText();
}
else if (GetKeyState('1') < 0)
{
state.reset(new Derived1());
displayText.clear();
displayText = state->getText();
}
}
return 0;
}
When pressing "1" and "2" back and forth it seems to work sometimes, and when I exit out I get something like -1073741510 or similar as the return value. In my game code it also seems to crash a lot.
(By exit out I mean using the X button on the command window, sorry for not clarifying)
After doing some research on unique_ptr and pointers in general along with polymorphic classes I still can't understand why this behaves the way it does.
So, what's going on here?

Answer 1

You are creating a shared_ptr from a stack variable. This will end up calling delete on p which is not safe. See Calling delete on variable allocated on the stack
EDIT:
You would need to make p a pointer. You could do something like the following:
class Base
{
public:
std::shared_ptr<std::string> p;
virtual ~Base()
{
}
virtual std::vector<std::shared_ptr<std::string>> getText() = 0;
};
class Derived1 : public Base
{
public:
Derived1()
{
p = std::make_shared<std::string>("from1");
}
std::vector<std::shared_ptr<std::string>> getText()
{
return std::vector<std::shared_ptr<std::string>>{p};
}
};
class Derived2 : public Base
{
public:
Derived2()
{
p = std::make_shared<std::string>("from2");
}
std::vector<std::shared_ptr<std::string>> getText()
{
return std::vector<std::shared_ptr<std::string>>{p};
}
};