25 Constructors in C++

1. Constructors

Reason: When we instantiate the Entity class and allocate memory, the memory is not actually initialized yet.

std::cout << e.X << std::endl; // C(compilation error): uninitialized local variable 'e' used

Common Practice:

Constructor

A constructor is a special type of method that is primarily used here. It is called whenever you create an object ^0156ab.

class Entity
{
public:
    float X, Y;

    Entity()   // Constructor
    {
        X = 0.0f;
        Y = 0.0f;
    }

    void Print()
    {
        std::cout << X << "," << Y << std::endl;
    }
};

int main()
{
    Entity e;
    std::cout << e.X << std::endl;  // 0
    e.Print();  // 0,0
    std::cin.get();
};

Default Constructor

The default constructor is provided by default, which is essentially like an empty function body that does nothing.

Entity()  // Default constructor, similar to
{
}

No variables are initialized.

In C++, you must manually initialize all primitive types, otherwise they will be set to whatever value was previously left in memory.

2. Function Overloading

You can write multiple constructors with the same name but provide different parameters.

When creating an object instance using the new keyword, the constructor is also called. I only want others to use this class like Log::Write, and I don't want others to create instances.

a. Setting the Constructor to Private

class Log
{
private:
    Log(){}
public:
    static void Write()
    {
    }
};

int main()
{
    Log::Write();
    Log l;
}

Or use

b. Delete

Log() = delete;

Deletes the default constructor.