CODEWITHSUNDEEP
c++g++
Suvarna Pattayil
Suvarna Pattayil

Reputation: 5239

Cascading overloaded cout operator error `No match` when used with other overloaded operators

I have overloaded << in my code as a friend function. Even after using braces while cascading there is still the error 

error: no match for ‘operator<<’ in ‘std::operator<< [with _Traits = 
std::char_traits<char>]((* & std::cout), ((const char*)"complex conjugate is ")) 
<< c.myComplex::operator~()’

I have a class myComplex 

class myComplex
{
    private:
    float real;
    float imaginary;    

    public:
    myComplex();
    myComplex(float a,float b);
    friend std::ostream& operator<<(std::ostream& iso,myComplex& a);
    myComplex operator~() const;
};

The overload for <<, ~and the constructors are as follows,

std::ostream& operator<<(std::ostream& oso,myComplex& a)
{
    oso<<a.real<<" + "<<a.imaginary<<"i"<<std::endl;
return oso;
}

myComplex myComplex::operator~() const
{
    return myComplex(this->real,-1*this->imaginary);
}

myComplex::myComplex(float a,float b)
{
    real = a;
    imaginary = b;
}

I use it in main as follows,

Line 1:    std::cout << "c is " << c << "\n";
Line 2:    std::cout << "a is " << a << "\n";

Line 3: ((std::cout <<"complex conjugate is ")<<(~c))<<"\n";

Line 3:    std::cout <<"complex conjugate is "<<~c<<"\n";

Line 1 and 2 work fine, but Line 3 gives the error. If it can cascade for Line 1 and 2 and since ~c also returns an ostream why does it give an error for that?

Upvotes: 0

Views: 406

Answers (4)

juanchopanza
juanchopanza

Reputation: 227438

Because your operator~() returns by value, you are feeding a temporary object into your ostream& operator<< here:

std::cout <<"complex conjugate is "<< ~c <<"\n";
//                                    ^^ HERE! Temporary myComplex value.

The operator takes its 2nd argument by non-const reference myComplex&. A non-const reference cannot bind to a temporary. Change it to

std::ostream& operator<<(std::ostream& oso, const myComplex& a);

Upvotes: 2

Angew is no longer proud of SO
Angew is no longer proud of SO

Reputation: 171127

Your operator << takes the second parameter by non-const reference, which means it can't bind to a temporary (such as the one returned by ~). Change operator << to accept const myComplex& as the second argument.

It would certainly be weird if the stream-output operator modified its argument anyway.

BTW, do you know that C++ has a built-in class std::complex?

Upvotes: 1

hmjd
hmjd

Reputation: 121971

A temporary object (in this case that returned by operator~()) cannot be bound to a non-const reference. Change argument of operator<<() to be a const reference:

friend std::ostream& operator<<(std::ostream& iso,myComplex const& a);

Upvotes: 3

trojanfoe
trojanfoe

Reputation: 122391

Use const myComplex & instead of myComplex &:

friend std::ostream& operator<<(std::ostream& iso, const myComplex& a);
                                                   ^^^^^

And change the implementation, of course.

Upvotes: 2

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