non-member function operator+(…) cannot have cv-qualifier

Question

I am currently writing a program to simulate gas in a box. But I have come across an issue with class operators. Unfortunately to make things annoying the class is called Vector, I know some won't like it being called this.

Vector.h

class Vector {
private:

double x;
double y;
double z;

public:

Vector & operator+=(const Vector & v){
    x += v.x;
    y += v.y;
    z += v.z;
    return *this;
}

I have editted the code above to make this problem clearer. I have left out the constructer etc as they dont effect the problem.

And for .cpp

Vector.cpp

Vector operator+(const Vector v) const{
Vector v2(*this);
v2+=v;
return v2;
}

And his yeilds error:

C:\\Users\\XXXXX\\ClionProjects\\XXXXX\\YYYYY\\Vector.cpp:95:34: error: non-member function 'Vector operator+(Vector)' cannot have cv-qualifier

C:\\Users\\XXXXX\\ClionProjects\\XXXXX\\YYYYY\\Vector.cpp: In function 'Vector operator+(Vector)':

Any help greatly appreciated.

Answer 1

The error tells you what's wrong. You made these non-member functions, but they should be member functions. The compiler detected the problem by your (correct) use of const , though the number of arguments is also lacking and that would be a further compilation error once the first was fixed.

Either you forgot to put these function definitions inside the class Vector { ... }; area, or you forgot to write Vector:: before operator .

Answer 2

Only member functions can have const specifiers. Both your operators are non-member functions (because they are missing class name as part of their signature) and are not defined inside the class definition.

As a result, you have a compilation error.

To fix this error you need to translate operator+ to a free function: remove it's declaration from your Vector class and change it's sigature to (the easiest form):

Vector operator+ (const Vector& lhs, const Vector& rhs);

There are certain reasons to use a different signature, and accept first argument by value, but this is way too deep for your level, so I suggest to stick to const reference for now.

Answer 3

Thanks for the other inputs, Both have merit to them. I have found my own answer based off of The answer given by Barry @BarryTheHatchet. And other sources. To solve this problem I moved the definition within the header file in the public section, giving me:

 Vector & operator+=(const Vector & v){
    x += v.x;
    y += v.y;
    z += v.z;
    return *this;
}

Vector operator+(const Vector v) const {
    Vector VecPlus(*this);
    VecPlus.x += v.x;
    VecPlus.y += v.y;
    VecPlus.z += v.z;
    return VecPlus;
}

This was the result, I do hope it is a legitimate way to code it and not a shody way to do it but would lead to later problems. I've advanced in my project and it has raised none so far.