Question

在我的任务中，我仍然有点卡在另一部分上。

以下是提示的要求：

现在您可以修改LoadMovies函数以创建MovieList   对象并将每个Movie对象添加到它。功能   LoadMovies应该返回一个指向MovieList对象的指针。这意味着   你需要动态地在堆上创建MovieList对象。

更改main函数并将返回的MovieList指针存储在a中   变量。要测试一切是否按预期工作，您可以使用   MovieList对象的PrintAll函数。

到目前为止，这是我的代码：

class MovieList {

public:
    Movie* movies;
    int last_movie_index;
    int movies_size;
    int movie_count = 0;

MovieList(int size) {
    movies_size = size;
    movies = new Movie[movies_size];
    last_movie_index = -1;
}

~MovieList() {
    delete [] movies;
}

int Length() {
    return movie_count;
}

bool IsFull() {
    return movie_count == movies_size;
}

void Add(Movie const& m)
{
    if (IsFull())
    {
        cout << "Cannot add movie, list is full" << endl;
        return;
    }

    ++last_movie_index;
    movies[last_movie_index] = m;
}

void PrintAll() {
    for (int i = 0; i < movie_count; i++) {
        movies[last_movie_index].PrintMovie();
    }
}

};

void ReadMovieFile(vector<string> &movies);
void LoadMovies();

enum MovieSortOrder
{
    BY_YEAR = 0,
    BY_NAME = 1,
    BY_VOTES = 2
};

int main()
{
    LoadMovies();

    // TODO:
    // You need to implement the Movie and MovieList classes and
    // the methods below so that the program will produce
    // the output described in the assignment.
    //
    // Once you have implemented everything, you should be able
    // to simply uncomment the code below and run the program.

    MovieList *movies = LoadMovies();

    //    // test methods for the Movie and MovieList classes
        //PrintAllMoviesMadeInYear(movies, 1984);
        //PrintAllMoviesWithStartLetter(movies, 'B');
        //PrintAllTopNMovies(movies, 5);

        //delete movies;
    return 0;
}

void LoadMovies()
{
    vector<string> movies;
    ReadMovieFile(movies);

    string name;
    int year;
    double rating;
    int votes;

    for (int i = 0; i < movies.size(); i++)
    {
        istringstream input_string(movies[i]);
        getline(input_string, name, '\t');
        input_string >> year >> rating >> votes;
        Movie movie (name, year, votes, rating);
        movie.PrintMovie();
    }
}

现在，我被困在哪里，教授要求我修改提示中的LoadMovies并将其转换为指针。我画的是空白。出于某种原因，如果我尝试编译它说：

C:\Users\Andy\Documents\C++ Homework\MovieStatisticsProgram\MovieStatsProgram.cpp:163: error: void value not ignored as it ought to be
     MovieList *movies = LoadMovies();
                                    ^

Answer 1

构造函数的顺序错误

MovieList(int size) {
    movies = new int[movies_size];  // movies_size hasn't been initialized yet!
    movies_size = size;
    last_movie_index = -1;
}

应该是

MovieList(int size)
:  movies_size{size}, movies{new int[size]}, last_movie_index{0}
{}

虽然@ ScottMcP-MVP指出你的阵列应该是

Movie* movie;

所以你的建造者将是

MovieList(int size)
:  movies_size{size}, movies{new Movie[size]}, last_movie_index{0}
{}

关于开始使用剩余功能的一些建议

Length函数将返回last_movie_index当前使用的数量。

IsFull会检查last_movie_index == movies_size - 1

Add需要使用last_movie_index来确定数组中存储电影的元素。

PrintAll必须从[0]迭代到[movie_count]并打印出每个元素。

您的Add功能看起来像

void MovieList::Add(Movie const& m)
{
    if (IsFull())
    {
        std::cout << "Cannot add movie, list is full" << std::endl;
        return;
    }

    movies[last_movie_index] = m;   // assigns a copy to your array
    ++last_movie_index;             // Increment the movie index
}

C ++ MovieList数组和指针

1 个答案: