CODEWITHSUNDEEP
c++constants
raging_subs
raging_subs

Reputation: 879

error: passing ‘const ComplexNumber’ as ‘this’ argument of ‘const ComplexNumber& ComplexNumber::operator-=(const Complex)

I have received the error message. 

 ComplexNumber.cpp: In function ‘ComplexNumber operator-(const ComplexNumber&, const ComplexNumber&)’:
    ComplexNumber.cpp:79:27: error: passing ‘const ComplexNumber’ as ‘this’ argument of ‘const ComplexNumber& ComplexNumber::operator-=(const ComplexNumber&)’ discards qualifiers [-fpermissive]
      return lhs.operator-=(rhs);

I have tried changing the return of the overloaded function operator- to be ComplexNumber(real, imag), but then I receive an error message of 

ComplexNumber.cpp:61:33: warning: returning reference to temporary [-Wreturn-local-addr]

I'm not sure why I'm getting the first error message. I have researched a bunch and have believe that it might have to do with const. How do I get rid of this error? Why is it happening?

The code is.

//defined -= operator
const ComplexNumber& ComplexNumber::operator-=(const ComplexNumber& rhs){
    real = real - rhs.real;
    imag = imag - rhs.imag;
    return *this;   
}

ComplexNumber operator-(const ComplexNumber& lhs, const ComplexNumber& rhs){
    return lhs.operator-=(rhs);
}

Upvotes: 0

Views: 169

Answers (1)

Luchian Grigore
Luchian Grigore

Reputation: 258618

Your operator - shouldn't modify lhs, so either create a copy, modify that and return it, or pass by value:

ComplexNumber operator-(ComplexNumber lhs, const ComplexNumber& rhs){
    return lhs.operator-=(rhs);
}

I'd use this one in order to allow the compiler to perform a move instead of creating your own copy inside the function (if you pass by reference).

Upvotes: 2

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