I'm rewriting an application using c++11 smart pointers.
I have a base class:
class A {};
And a derived class:
class B : public A {
public:
int b;
};
I have another class containing a vector with either A or B objects:
class C {
public:
vector<shared_ptr<A>> v;
};
I have no problem constructing C with A (base class) objects but how can I fill it with B (derived class) objects?
I'm trying this:
for(int i = 0; i < 10; i++) {
v.push_back(make_shared<B>());
v.back()->b = 1;
};
And the compiler returns: error: 'class A' has no member named 'b'
But how can I fill it with B (derived class) objects?
You are filling it with (pointers to) B
objects. However, the pointers' static type refers to the base class A
, so you cannot directly use these to access any members of the derived class.
In your simple example, you could simply keep hold of a pointer to B
and use that:
std::shared_ptr<B> b = make_shared<B>();
b->b = 1;
v.push_back(b);
If you don't have access to the original pointer, then you will need some kind of polymorphism:
static_cast<B*>(v.back().get())
if you know that all objects have type B
dynamic_cast
(which requires the base class to contain a virtual function to work) if the objects might have different types for(int i = 0; i < 10; i++) {
auto bptr = make_shared<B>();
v.push_back(bptr);
bptr->b = 1;
};
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