Overloading the new operator

Question

I have a problem with Overloading operator 'new' in my class.

Code:

time.h

#ifndef TIME_H_
#define TIME_H_

#include <cstddef>
#include <stdlib.h>

class Time {
private:
    int hours;
    int minutes;

public:
    Time(int a = 0, int b = 0) : hours(a), minutes(b) {};

    void AddMin(int m);
    void AddHours(int h);
    void Reset(int h = 0, int m = 0);
    void Show() const;

    Time Suma(const Time & t) const;


    //przeladowania
    void* operator new(size_t);

};
#endif

time.cpp

 #include "time.h"
#include <iostream>
#include <cstddef>
#include <stdlib.h>

void Time::AddMin(int m)
{
    this->minutes += m;
    this->hours += this->minutes / 60;
    this->minutes += this->minutes % 60;
}

void Time::AddHours(int h)
{
    this->hours += h;
}

void Time::Reset(int h, int m)
{
    this->hours = h;
    this->minutes = m;
}

void Time::Show() const
{
    std::cout << this->hours << " hours and " << this->minutes << " minutes" << std::endl;
}

////overloading
void* Time::operator new(size_t size)
{
    void *storage = malloc(size);
    if (NULL == storage) {
        throw "allocation fail : no free memory";
    }
    std::cout << storage << std::endl;
    Time * time = (Time*)storage;
    time->minutes = 12;

    return time;
}

prog.cpp

#include <iostream>
#include "time.h"

int main()
{
    Time * timeNew = new Time();
    timeNew->Show();
    std::cout << timeNew << std::endl;

    return 0;
}

And results - addreses:

0104F5E8
0 hours and 0 minutes
0104F5E8

I don't understand why my objects have other adresses in memory. I think if I return pointer, so my object timeNew(in prog.cpp) should have the same adress as storage in time.cpp.

I konw it's a function, but I used pointer, so it shouldn't delete after return to program.

Why timeNew has 0 hours and 0 minutes? I sign value in function.

Could you explain me what I do wrong?

Answer 1

Note: as StoryTeller pointed out in the comments, accessing an object before the constructor was called is generally a very bad practice and potentially prone to dangerous bugs. It's also almost never necessary. Unless you are knowingly implementing a dirty hack, you should probably not do this. Keep in mind that the new operator in c++ is absolutely different from what you might find in python for instance, where it's used to created immutable types.

Why timeNew has 0 hours and 0 minutes? I assign a value in the new function.

This happens because after the operator new, the constructor is called and since you pass no argument, the constructor will reset the values for minute and hours after you assigned 12 to minutes.

If you want to see the effect of this assignment in operator new, simply change:

 Time(int a = 0, int b = 0) : hours(a), minutes(b) {};

with:

 Time(int a, int b) : hours(a), minutes(b) {};
 Time() {};