Custom C++ smart_ptr for the sake of exsercise...

smartptr.cpp

#include <cstdio>

template<typename T>
class smartptr {
    public:
    smartptr(T* v) : _data(new data(v)) {
        printf(" * smartptr: obtained value %d\n", *_data->value);
    }

    smartptr(const smartptr &other) : _data(other._data) {
        _data->refcount++;
        printf(" * smartptr: copied pointer for value %d (ref: %lu)\n", **_data, _data->refcount);
    }

    ~smartptr() {
        reset();
    }

    void operator=(const smartptr &other) {
        reset();
        _data = other._data;
        _data->refcount++;
        printf(" * smartptr: data reassigned to value %d (ref: %lu)\n", **_data, _data->refcount);
    }

    T& operator*() {
        return **_data;
    }

    void reset() {
        if (_data != nullptr && --_data->refcount == 0) {
            printf(" * smartptr: destroying data [%d]\n", **_data);
            delete _data->value;
            delete _data;
            _data = nullptr;
        } else if (_data) {
            printf(" * smartptr: ref--(%d) -> %ld\n", **_data, _data->refcount);
        } else {
            printf(" * smartptr: reset(<null>)\n");
        }
    }

    private:
    class data {
        public:
        T* value;
        unsigned long refcount = 1;

        data(T* v) : value(v) {}
        data(const data &other) = delete;
        T& operator*() {
            return *value;
        }
    };

    data* _data;
};


int main(int argc, char **argv) {
    smartptr<int> y(new int(1234));
    smartptr<int> z = y;

    printf("y: %d\n", *y);

    y = smartptr<int>(new int(999));

    printf("z: %d\n", *z);
    return 0;
}