How to properly use pointers with class functions

Question

What is the proper way to implement this class function when using pointers. I understand the basics of pointers, but it gets confusing. I'm trying to create a function that adds fractions.

f3 =  f1->add(f2);

Everything else in the class is running correctly.

#include <iostream>
using namespace std;

//members of a class default to private
class Fraction
{
private:
    int numerator;
    int denominator;

public:
    Fraction();
    Fraction(int,int);
    ~Fraction();
    Fraction* add(Fraction &f);
    void setFraction(int, int);
    int getNumerator();
    int getDenominator();
    };
Fraction::Fraction()
{
    numerator = 0;
    denominator = 0;
}
Fraction::Fraction(int num, int den)
{
    this->numerator = num;
    this ->denominator = den;
}
Fraction::~Fraction()
{
}
void Fraction::setFraction(int num, int den)
{
    numerator = num;
    denominator = den;
}
int Fraction::getNumerator()
{
    return numerator;
}
int Fraction::getDenominator()
{
    return denominator;
}
Fraction* Fraction::add(Fraction &f)
{
    int num = f.numerator * this->denominator;
    num += this->numerator *f.denominator;
    int den = this->denominator * f.denominator;
    return new Fraction(num,den);
}

int main() {
    Fraction* f1 = new Fraction(5,8);
    Fraction* f2 = new Fraction(1,8);
    cout << f1->getNumerator() << "/" << f1->getDenominator() <<endl;
    Fraction* f3 = new Fraction();
    f3 =  f1->add(f2);
    return 0;
}

The parameter is a reference, not a pointer. And you should not be returning pointers to newed objects, but objects by value. — juanchopanza
– juanchopanza, Commented Sep 30, 2016 at 14:14
Your function signature takes a reference (Fraction &f) but you're passing a pointer by using new so you can change to do f3 = f1->add(Fraction(1,8)) — EdChum
– EdChum, Commented Sep 30, 2016 at 14:15
@TimBotelho if you include that error in your question, it will help others to answer. — apple apple
– apple apple, Commented Sep 30, 2016 at 14:24
You really don't want to be using pointers here, let alone dynamic allocation. — juanchopanza
– juanchopanza, Commented Sep 30, 2016 at 14:27

Paul Evans · Accepted Answer · 2016-09-30 14:20:41Z

2

If you want to pass in a pointer into a function (doesn't matter if it's a member or not), make the function signature that way:

Fraction* Fraction::add(Fraction* f)
                                ^ pass a pointer in

answered Sep 30, 2016 at 14:20

Paul Evans

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1 Comment

juanchopanza Over a year ago

OP doesn't really want to do this!

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