Question

I have a class that has only one function “Print()” and two properties “age, sex”. And i am trying to understand when is object creating on memory?

i can always access to object’s props and functions even i didn’t call it’s constructor function.

Isn’t there any rule for the creating object from the class?

In C# this won’t create object on memory: ClassName cls;
But this will create: ClassName cls = new ClassName();
In C++ is there any way to not create object in memory until i need to call it’s constructor function?

#include <QtCore/QCoreApplication>
#include "iostream"

using namespace std;

class ClassName{
public:
    void print(){
        cout<< "Age: " <<age <<endl;
        cout<< "Sex: " <<sex <<endl;
    }
    int age;
    char sex;


};


int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    ClassName *ex1 = new ClassName();
    ex1->print();

    ClassName ex2;
    ex2.print();

    ClassName ex3= {10,'e'};
    ex3.print();

    ClassName exCopy(ex3);
    exCopy.print();

    return a.exec();
}

Answer 1

In C# this willn’t create object on memory: ClassName cls; But this will create: ClassName cls = new ClassName(); In C++ is there any way to not create object in memory until i need to call it’s constructor function?

The equivalent to your C# example, using C++, is as follows:

//pointer to ClassName, not initialized
ClassName* cls1;
//alternatively
ClassName* cls2 = 0;
//initialize after declaring it but before using it
cls1 = new ClassName();
cls1->print();
//after initializing it, don't forget to delete it again later
delete cls1;
cls1 = 0;
//this is an error (using uninitialized pointer)
cls2->print();

C# classes are ‘reference’ types, which are like C++ ‘pointer’ types.