C++ - trying to overload "<<" operator

Question

I am trying to overload "<<" operator to call 2 methods but compiler gives me an error:

invalid initialization of non-const reference of type 'std::ostream&' 
{aka 'std::basic_ostream<char>&' from an rvalue of type 'void'
        return v.init();

Here is my class definition:

template<class T>
class Vector
{
private:
    std::vector<T> _Vec;
public:
    void fillVector();
    void printElements();
    void init() { fillVector(); printElements(); }
    friend std::ostream& operator<<(std::ostream& os, Vector& v) {
            return v.init();    
};

How can I fix it?

`return os;`, not the result of `v.init();` (which is `void`) — Piotr Skotnicki, Jun 11 '18 at 15:42
`_Vec` is a [reserved identifier](https://stackoverflow.com/q/228783/3953764) — Piotr Skotnicki, Jun 11 '18 at 15:43
I expect you also need to modify `printElements` to use `os`. — drescherjm, Jun 11 '18 at 15:46

score 1 · Accepted Answer · answered Jun 11 '18 at 16:01

You're doing that wrong.

This template is misleading. Its name is terrible.
This extra methods: fillVector, printElements, init are confusing (what exactly they should do?).
Most probably printElements is missing std::ostream& stream argument (and maybe return type).

You didn't described what kind of functionality you are trying to implement. Most probably this is what you need:

template<class T>
class PrintContainer
{
public:
    PrintContainer(const T& container)
    : mContainer { container }
    {}

    std::ostream& printTo(std::ostream& stream) const {
        // or whatever you need here
        for (const auto& x : mContainer) {
             stream << x << ", ";
        }
        return stream;
    }

private:
    const T& mContainer;
};

template<class T>
std::ostream& operator<<(std::ostream& os, const PrintContainer<T>& p) {
    return p.printTo(os);
}

C++ - trying to overload "<<" operator

1 Answers1