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Ivan Botero
Asked: 2020-03-27 09:45:06 +0800 CST 2020-03-27 09:45:06 +0800 CST

Unary operator overloading in C++

  • 772

I have created the following class.

class Persona{

private:
    std::string nombre;

public:
    std::string getNombre();
    Persona operator=(std::string nombre);

};

Persona Persona::operator=(std::string nombre){

    Persona persona;
    persona.nombre = nombre;

    return persona;
}

std::string Persona::getNombre(){
    return this->nombre;
}

As you can see, the operator is overloaded =:

Persona operator=(std::string nombre);

What I want is to be able to assign the value to the attribute nombreusing the operator =.

Leaving my code like this:

#include <iostream>
#include <cstdlib>
#include <string>

class Persona{

private:
    std::string nombre;

public:
    std::string getNombre();
    Persona operator=(std::string nombre);

};

Persona Persona::operator=(std::string nombre){

    Persona persona;
    persona.nombre = nombre;

    return persona;
}

std::string Persona::getNombre(){
    return this->nombre;
}

int main(void)
{

    Persona p;

    p = "John Doe";

    std::cout << "Nombre: " << p.getNombre() << std::endl;

    return EXIT_SUCCESS;
}

When compiling, there are no errors, based on what I've read, the operator =makes a return, and this is assigned to the object where it is used:

p = "John Doe";

But! When I run the program, I get this:

Name:

Process returned 0 (0x0) execution time : 0.015 s

Press any key to continue.

The value that should be assigned is not assigned, leaving the name empty.

What mistake am I making in overloading operator = ?

c++

1 Answers

  1. Best Answer

    The correct thing would be (I show it inline for brevity):

    class Persona{
private:
  std::string nombre;

public:
  Persona &operator=( std::string nnombre ) {
    nombre = nnombre;
    return *this;
  }
};

    To access the members of our own class, we don't need to precede them with the class name; all members become accessible from the body of the functions, as if they were local variables of the function. It is a facility that the language offers to the programmer.

    For the same reason, it is not necessary to access them as this->ALGO; that would be used in case of name conflict; for example, receiving a method argument with the same name as an attribute of the class.

    In your original code, inside operator=( ), you create a new instance of the class Persona, assign to that instance, and then return that instance you created. Doing so leaves the original instance intact .

    Also notice that I have changed the return value of your operator=. Instead of returning an instance, I return a reference to the original instance .

    • 3