C++ Push back a vector into a vector

Question

This is the vector I created;

std::vector<std::vector<Vertex*>*> Vertices;

And I'm having trouble figuring out how to push back the std::vector<Vertex*> into the outer vector.

So what im kind of trying to do is:

Vertices.push_back(new vector().push_back(new Vertex()));

but I'm not sure what the right way to do it is. Hope you people get the idea.

Answer 1

Although it is sometimes OK to make a vector of pointers (preferably, smart pointers), it is never a good idea to make a vector of pointers to vectors: this complicates your memory management for no good reason.

The best solution is to use a vector of vertex objects, like this:

std::vector<std::vector<Vertex> > vertices;

This would let you push back like this:

vector<Vertex> vv;
vv.push_back(Vertex(...));
vertices.push_back(std::move(vv));

If you want a vector of descendants of Vertex with polymorphic behavior, use a vector of vectors of pointers:

std::vector<std::vector<Vertex*> > vertices;
...
vector<Vertex*> vv;
vv.push_back(new Vertex(...));
vertices.push_back(std::move(vv));

Note that if you do this, you are on the hook for freeing the Vertex objects inside the vector. A better solution would be using smart pointers - say, std::unique_ptr, like this:

std::vector<std::vector<std::unique_ptr<Vertex>>> vertices;

std::unique_ptr would take care of freeing Vertex objects automatically.