CODEWITHSUNDEEP
c++
chlong
chlong

Reputation: 445

overloading operator== complaining of 'must take exactly one argument'

I am trying to overload the operator==, but the compiler is throwing the following error:

‘bool Rationalnumber::operator==(Rationalnumber, Rationalnumber)’ must take exactly one argument

My short piece of code is as follows:

bool Rationalnumber::operator==(Rationalnumber l, Rationalnumber r) {
  return l.numerator() * r.denominator() == l.denominator() * r.numerator();
}

Declaration:

bool operator==( Rationalnumber l, Rationalnumber r );

Does anyone have any ideas why it's throwing the error?

Upvotes: 11

Views: 32289

Answers (4)

yucun li
yucun li

Reputation: 11

friend bool operator==( Rationalnumber l, Rationalnumber r );

when you declare it as non-member function, it can take two arguments. when you declare it as member function, it can only take one argument.

Upvotes: 1

juanchopanza
juanchopanza

Reputation: 227578

If operator== is a non static data member, is should take only one parameter, as the comparison will be to the implicit this parameter:

class Foo {
  bool operator==(const Foo& rhs) const { return true;}
};

If you want to use a free operator (i.e. not a member of a class), then you can specify two arguments:

class Bar { };
bool operator==(const Bar& lhs, const Bar& rhs) { return true;}

Upvotes: 22

Plexico
Plexico

Reputation: 131

As a member operator overload it should only take one argument, the other being this.

class Foo
{
    int a;

public:
    bool operator==(const Foo & foo);
};

//...

bool Foo::operator==(const Foo & foo)
{
    return a == foo.a;
}

Upvotes: 4

tim-oleksii
tim-oleksii

Reputation: 133

You should remove your operator== from a RationalNumber to somewhere else. As it is declared inside a class it is considered that 'this' is the first argument. From semantics it is seen that you offer 3 arguments to a compiler.

Upvotes: 2

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