C++ Vector of pointers

For my latest CS homework, I am required to create a class called Movie which holds title, director, year, rating, actors etc.

Then, I am required to read a file which contains a list of this info and store it in a vector of pointers to Movies.

I am not sure what the last line means. Does it mean, I read the file, create multiple Movie objects. Then make a vector of pointers where each element (pointer) points to one of those Movie objects?

Do I just make two vectors – one of pointers and one of Movies and make a one-to-one mapping of the two vectors?

4 Answers

It means something like this:

std::vector<Movie *> movies;

Then you add to the vector as you read lines:

movies.push_back(new Movie(...));

Remember to delete all of the Movie* objects once you are done with the vector.

As far as I understand, you create a Movie class:

class Movie
{
private:
  std::string _title;
  std::string _director;
  int         _year;
  int         _rating;
  std::vector<std::string> actors;
};

and having such class, you create a vector instance:

std::vector<Movie*> movies;

so, you can add any movie to your movies collection. Since you are creating a vector of pointers to movies, do not forget to free the resources allocated by your movie instances OR you could use some smart pointer to deallocate the movies automatically:

std::vector<shared_ptr<Movie>> movies;

By dynamically allocating a Movie object with new Movie(), you get a pointer to the new object. You do not need a second vector for the movies, just store the pointers and you can access them. Like Brian wrote, the vector would be defined as

std::vector<Movie *> movies

But be aware that the vector will not delete your objects afterwards, which will result in a memory leak. It probably doesn’t matter for your homework, but normally you should delete all pointers when you don’t need them anymore.

I am not sure what the last line means. Does it mean, I read the file, create multiple Movie objects. Then make a vector of pointers where each element (pointer) points to one of those Movie objects?

I would guess this is what is intended. The intent is probably that you read the data for one movie, allocate an object with new, fill the object in with the data, and then push the address of the data onto the vector (probably not the best design, but most likely what’s intended anyway).

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