defining copy constructor and assignment operator

Question

It's my first time dealing with classes in C++. I was wondering if somebody could help me to properly design a copy constructor and an assignment operator for the following class.

The following post talks about the rule of threes,

What is The Rule of Three?

Although, it was not very clear how to implement it for my code.

INFO.h

#ifndef INFO_H
#define INFO_H

class INFO{
public:
        std::string label, type;
        unsigned int num;
        double x, y, z, velx, vely, velz;
        void print(std::ostream& stream);
        void mod_print(std::ostream& stream);
        void read(std::istream& stream);
        void mod_read(std::istream& stream);
        double distance(INFO *i,double L);
        INFO(std::istream& stream);
        INFO(){};
};

#endif

INFO.cpp

#include "INFO.h"

void INFO::print(std::ostream& stream)
{
        stream << label <<'\t'<< type <<'\t'<< num <<'\t'<< x<<'\t'<<y<<'\t'<< z << '\n';
}
void INFO::mod_print(std::ostream& stream)
{
        stream << label <<'\t'<< type <<'\t'<< x<<'\t'<<y<<'\t'<< z << '\n';
}
void INFO::read(std::istream& stream)
{
        stream >> label >> type >> num >> x >> y >> z;
}
void INFO::mod_read(std::istream& stream)
{
        stream >> label >> type >> x >> y >> z;
}
double INFO::distance(INFO *i,double L)
{
        double delx = i->x - x - std::floor((i->x-x)/L + 0.5)*L;
        double dely = i->y - y - std::floor((i->y-y)/L + 0.5)*L;
        double delz = i->z - z - std::floor((i->z-z)/L + 0.5)*L;
        return delx*delx + dely*dely + delz*delz;
}
INFO::INFO(std::istream& stream)
{
        stream >> label >> type >> num >> x >> y >> z;
}

don't use all caps locks for your id's. It's a convention for macros. Use `class info` or `class Info`. Never `class INFO` — bolov, Jun 10 '15 at 14:08

score 2 · Answer 1 · answered Jun 10 '15 at 14:03

2

Since your class contains these member variables

std::string label, type;
unsigned int num;
double x, y, z, velx, vely, velz;

In the copy constructor you copy the values present in the reference object. So, define the constructor as below

INFO::INFO(const INFO &Ref)
{
    // copy the attributes
    this->label = Ref.label;
    this->type = Ref.type;
    this->num = Ref.num;
    this->x = Ref.x;
    this->y = Ref.y;
    this->z = Ref.z;
    this->velx = Ref.velx;
    this->vely = Ref.vely;
    this->velz = Ref.velz;
}

For the assignment operator you need to write a function like this

INFO& INFO::operator= (const INFO &Ref)
{
    // copy the attributes
        this->label = Ref.label;
        this->type = Ref.type;
        this->num = Ref.num;
        this->x = Ref.x;
        this->y = Ref.y;
        this->z = Ref.z;
        this->velx = Ref.velx;
        this->vely = Ref.vely;
        this->velz = Ref.velz;

    // return the existing object
    return *this;
}

Hope this works, let me know

answered Jun 10 '15 at 14:03

Bharadwaj

737
6
26

When compiling its giving the following errors: ' error: definition of implicitly-declared ‘info::info(const info&)’ ' and ' error: definition of implicitly-declared ‘info& info::operator=(const info&)’ '. – user2804865 Jun 10 '15 at 14:24
Because you need to add the prototype in the INFO.h file also `INFO& INFO::operator= (const INFO &Ref);` and `INFO::INFO(const INFO &Ref);` – Bharadwaj Jun 10 '15 at 14:25
Would a destructor be designed in a similar manner? – user2804865 Jun 10 '15 at 14:35
You don't need a destructor unless you use dynamic memory allocation. Please refer to the basics of [OOPS](http://www.cplusplus.com/doc/tutorial/classes/) – Bharadwaj Jun 10 '15 at 14:37

defining copy constructor and assignment operator

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