Outputing a list separated by space

Question

I'm overloading operator << to output my container separated by space:

std::ostream& operator<< (std::ostream &os, const MyContainer &v)
{
    os << "[";
    for (const auto &i : v) {
        os << i << " ";
    }
    os << "\b]"; // <--
    return os;
}

MyContainer c{1,2,3};
std::cout<<c<<std::endl;

I'm using '\\b' to avoid the extra space at the end of the list, it works fine with above code.

But it might not be a good idea, does '\\b' work well with other types of ostream ? Any other idea to output data like this?

Answer 1

But it might not be a good idea, does '\\b' work well with other types of ostream ?

You are absolutely right about this not being a good idea: '\\b' works fine in console mode, but it does not play well with other streams, such as files.

A better approach is to not output the extra space in the first place:

std::ostream& operator<< (std::ostream &os, const MyContainer &v)
{
    os << "[";
    auto first = true;
    for (const auto &i : v) {
        if (!first) {
            os << " ";
        } else {
            first = false;
        }
        os << i;
    }
    os << "]";
    return os;
}

Answer 2

A simple pragmatic solution is to just add a space before the range loop:

std::ostream& operator<< (std::ostream &os, const MyContainer &v)
{
    os << "[ "; // <--
    for (const auto &i : v) {
        os << i << " ";
    }
    os << "]";
    return os;
}

MyContainer c{1,2,3};
std::cout<<c<<std::endl;

The result is a slightly different output, but still achieves the presumed goal of visually pleasing symmetrical formatting: instead of [1 2 3] you get [ 1 2 3 ] . Empty lists will print as [ ] .