Comma Separate Number Without stringstream

Question

So typically if I wanted to insert locale appropriate separators in some number, foo, I'd do something like this:

ostringstream out;

out.imbue(locale("en-US"));
out << foo;

Then I could just use out.str() as the separated string: http://coliru.stacked-crooked.com/a/054e927de25b5ad0

Unfortunately I've been asked not to use stringstreams in my current project. Is there any other way I can accomplish this? Ideally a locale dependent way?

Answer 1

So this answer is the C++ distillation of Jerry Coffin's answer to this question: Cross Platform Support for sprintf's Format '-Flag

template <typename T>
enable_if_t<is_integral_v<remove_reference_t<T>>, string> poscommafmt(const T N, const numpunct<char>& fmt_info) {
    const auto group = fmt_info.grouping();
    auto posn = cbegin(group);
    auto divisor = static_cast<T>(pow(10.0F, static_cast<int>(*posn)));
    auto quotient = div(N, divisor);
    auto result = to_string(quotient.rem);

    while(quotient.quot > 0) {
        if(next(posn) != cend(group)) {
            divisor = static_cast<T>(pow(10.0F, static_cast<int>(*++posn)));
        }
        quotient = div(quotient.quot, divisor);
        result = to_string(quotient.rem) + fmt_info.thousands_sep() + result;
    }
    return result;
}

template <typename T>
enable_if_t<is_integral_v<remove_reference_t<T>>, string> commafmt(const T N, const numpunct<char>& fmt_info) {
    return N < 0 ? '-' + poscommafmt(-N, fmt_info) : poscommafmt(N, fmt_info);
}

Naturally this suffers from the identical 2's compliment negation issue.

This certainly benefits from C++'s string memory management, but also from the ability to pass in a specific numpunct<char> which need not be the current locale. For example whether or not cout.getloc() == locale("en-US") you can call: commafmt(foo, use_facet<numpunct<char>>(locale("en-US")))

Live Example

Answer 2

Set up a pipe. Use the linked to code to construct an ofstream and ifstream from a file descriptor and then output to one and read from the other.

This is a bizarre and contorted solution. But then the idea that you have to use locales, have to store things, and can't use stringstream is just as bizarre. So, they give you bizarre requirements, they get bizarre code.