How to convert a vector of parent pointers to another in c++?

Question

How to convert two parent pointers in c++? This is the code.

// base class
class B {
    public:
       virtual ~B() {};
    // other code
};
class A {
    public:
       virtual ~A() {};
    // other code
};

// child class
class C1 : public A, B {
    public:
       virtual ~C1() {};    
    // other code
};
class C2 : public A, B {
    public:
       virtual ~C2() {};
    // other code
};
// ...other C class

There is a std::vector<std::shared_ptr<A>> which items point to instance C1 or C2 ...Cn.
Does anyone know how to convert the vector to a std::vector<std::shared_ptr<B>>?

Answer 1

Your code has typos. Missing public in inheritance of B when defining C<x> breaks stuff.

After this is fixed sidecast does the job as it should:

dynamic_cast conversion - cppreference.com

b) Otherwise, if expression points/refers to a public base of the most derived object, and, simultaneously, the most derived object has an unambiguous public base class of type Derived, the result of the cast points/refers to that Derived (This is known as a "sidecast".)

// base class
class B {
public:
    virtual ~B() { }
};
class A {
public:
    virtual ~A() { }
};

class C1 : public A, public B {
public:
    virtual ~C1() { }
};

class C2 : public A, public B {
public:
    virtual ~C2() { }
};


TEST(SideCast, sigleItemCast)
{
    C2 x;
    A* a = &x;
    auto b = dynamic_cast<B*>(a);
    ASSERT_THAT(b, testing::NotNull());
}

TEST(SideCast, sideCastOfVectorContent)
{
    std::vector<std::shared_ptr<A>> v { std::make_shared<C1>(), std::make_shared<C2>() };
    std::vector<std::shared_ptr<B>> x;
    std::transform(v.begin(), v.end(), std::back_inserter(x), 
        [](auto p) { return std::dynamic_pointer_cast<B>(p); });

    ASSERT_THAT(x, testing::Each(testing::NotNull()));
}

Live demo