How do I change the thousands separator of my default locale?

Question

I can do

locale loc(""); // use default locale
cout.imbue( loc );
cout << << "i: " << int(123456) << " f: " << float(3.14) << "\n";

and it will output:

i: 123.456 f: 3,14

on my system. (german windows)

I would like to avoid getting the thousands separator for ints -- how can I do this?

(I just want the users default settings but without any thousands separator.)

(All I found is how to read the thousands separator using use_facet with the numpunct facet ... but how do I change it?)

Answer 1

Just create and imbue your own numpunct facet:

struct no_separator : std::numpunct<char> {
protected:
    virtual string_type do_grouping() const 
        { return "\000"; } // groups of 0 (disable)
};

int main() {
    locale loc("");
    // imbue loc and add your own facet:
    cout.imbue( locale(loc, new no_separator()) );
    cout << "i: " << int(123456) << " f: " << float(3.14) << "\n";
}

If you have to create a specific output for another application to read, you may also want to override virtual char_type numpunct::do_decimal_point() const;.

If you want to use a specific locale as base, you can derive from the _byname facets:

template <class charT>
struct no_separator : public std::numpunct_byname<charT> {
    explicit no_separator(const char* name, size_t refs=0)
        : std::numpunct_byname<charT>(name,refs) {}
protected:
    virtual string_type do_grouping() const
        { return "\000"; } // groups of 0 (disable)
};

int main() {
    cout.imbue( locale(std::locale(""),  // use default locale
        // create no_separator facet based on german locale
        new no_separator<char>("German_germany")) );
    cout << "i: " << int(123456) << " f: " << float(3.14) << "\n";
}