Essentially, I want 2 of my classes to be sharing some data, which i want to have as a vector of shared_ptr objects.
I have cut down my code into the following simple compilable example.
I want object A, to be looking at the data that was initialized in object B. However when I try and do push_back() inside a method of A, it hasnt changed the size of the vector of shared_ptr objects in B. (At the line with the comment "This is the point of interest".)
What approach do I need to use to get this functionality, or am I on the wrong track. (c++ newbie here)
#include <memory>
#include <vector>
#include <iostream>
using std::cout;
using std::endl;
class DataClass {
public:
int i_;
};
class B {
public:
// constructor:
B() : my_data_(std::vector<std::shared_ptr<DataClass> >()) {
my_data_.push_back(std::shared_ptr<DataClass> (new DataClass));
my_data_.push_back(std::shared_ptr<DataClass> (new DataClass));
my_data_[0]->i_ = 1;
my_data_[1]->i_ = 2;
cout<<my_data_.size()<<endl;
};
// return the data
std::vector< std::shared_ptr<DataClass> > get_my_data() {
return my_data_;
};
// check the data:
void CheckData() {
cout<<my_data_.size()<<endl; // This is the point of interest
};
// member variable
std::vector< std::shared_ptr<DataClass> > my_data_;
};
class A {
public:
void start() {
// begin interaction with B class:
B b;
// get the vector of data pointers:
a_has_data_ = b.get_my_data();
// modify some of the data:
a_has_data_.push_back(std::shared_ptr<DataClass> (new DataClass));
a_has_data_[2]->i_ = 42;
b.CheckData();
};
private:
std::vector< std::shared_ptr<DataClass> > a_has_data_;
};
int main() {
A a;
a.start();
}
You are returning a copy of the vector. You need to return a reference to the data:
// return the data
std::vector< std::shared_ptr<DataClass> >& get_my_data()
{
return my_data_;
};
That was A
is accessing b
's vector, not a copy of it.