CODEWITHSUNDEEP
c++classconstructor
David Salazar
David Salazar

Reputation: 133

c++ 2 constructors and a destructor in a class

This is correct code from a classmate the professor bragged about and I cant understand why it requires a double constructor i originally only had the first function and couldnt figure out it required two which lagged my progress as a professional

class Studentrecords
{
private:

    struct student
    {
        string name;
        string address;
        int ID;
        double gpa;
    };

    student *stackArray;
    int stackSize;
    int top;

public:
    Studentrecords();
    Studentrecords(int size);
    ~Studentrecords();
    void push(string name, string address, int id, double gpa);
    void pop();
    bool isFull() const;
    bool isEmpty() const;
    void display();
};

Studentrecords::Studentrecords(int size)
{
    stackArray = new student[size];
    top = 0;
}

Studentrecords::Studentrecords()
{
    stackSize = 25;
    stackArray = new student[stackSize];
    top = 0;
}

Studentrecords::~Studentrecords()
{
    delete [] stackArray;
}

Upvotes: 0

Views: 13167

Answers (3)

juanchopanza
juanchopanza

Reputation: 227588

The second constructor allows you to initialize a StudentRecords to a given size. This is convenient, but not strictly necessary. Unfortunately, is also allows an implicit conversion from int to StudentRecords, which you can disable by making it explicit.

explicit Studentrecords(int size);

That will prevent nonsense such as

StudentRecords s = 4*5;

A more important fact is that your class deals with dynamically allocated resources, so you must follow the rule of three and provide a copy constructor and a copy assignment operator, besides the destructor that you have already provided.

Upvotes: 4

David Schwartz
David Schwartz

Reputation: 182885

The code doesn't require two constructors. A single constructor with a default argument is better. And the first constructor is broken, since it fails to set stackSize.

Upvotes: 0

Luchian Grigore
Luchian Grigore

Reputation: 258678

It doesn't require two constructors, that's just how the class is defined. That way, you can create an object in two ways:

Studentrecords s(15);

which will create a Studentrecords object of size 15, or

Studentrecords s;

which will call the default constructor, and create an object of type Studentrecords and size 25.

I must note that this is bad code though:

  • The default Studentrecords() constructor can be replaced with Studentrecords(int size = 25) to avoid code duplication.
  • no use of initializer lists
  • you're managing memory in the class, which means you'd need a copy constructor and copy assignment operator
  • finally, you're using a C-style array instead of a std::vector.

Upvotes: 7

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