CODEWITHSUNDEEP
c++templatesoperators
lo tolmencre
lo tolmencre

Reputation: 3934

operator<< in template function: invalid operands

I have a class Color, that has friend std::ostream& operator<<(std::ostream&, Color&). It looks like this:

struct Color
{
    Color(CID c, sstr s)
    :color(c),
    str(s)
    {
    }


    friend sost& operator<<(sost& o, Color& c)
    {
        o << "\033[1;" << c.color << "m" << c.str << "\033[0m";
        return o;
    }

    CID color;
    sstr str;
};

I can call the operator without any issue in all circumstances but in a templated function:

template<typename T>
void print_head(const T& head, sost& o)
{
    o << head << "\r";
    o.flush();
    spaces+=(headSize);
}

I invoke it with print_head<helper::Color>(rsym, o); with rsym being a instance of Color. And I get 

error: invalid operands to binary expression ('sost'
  (aka 'basic_ostream<char>') and 'const helper::Color')
            o << head << "\r";
            ~ ^  ~~~~
note: in instantiation of function template specialization
  'blk::Bouncer::print_head<helper::Color>' requested here
                            print_head<helper::Color>(rsym, o);

Whats wrong with the template function?

Upvotes: 1

Views: 261

Answers (1)

TheUndeadFish
TheUndeadFish

Reputation: 8171

Your operator takes a non const reference but head is const.

You should change it to 

friend sost& operator<<(sost& o, const Color& c)

Upvotes: 2

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