std::moneypunct::thousands_sep, do_thousands_sep

From cppreference.com
< cpplrm; | localelrm; | moneypunct
Defined in header <locale>
public:
char_type thousands_sep() const;
(1)
protected:
virtual char_type do_thousands_sep() const;
(2)
1) Public member function, calls the member function do_thousands_sep of the most derived class.
2) Returns the character to be used as the separator between digit groups when parsing or formatting the integral parts of monetary values.

Return value

The object of type char_type to use as the thousands separator. In common U.S. locales, this is ',' or L','.

Example

#include <locale>
#include <iostream>
#include <iomanip>
#include <iterator>
struct space_out : std::moneypunct<char> {
    pattern do_pos_format()      const { return { {value, none, none, none} };}
    int do_frac_digits()         const { return 0; }
    char_type do_thousands_sep() const { return ' ';}
    string_type do_grouping()    const { return "\002";}
};
int main()
{
    std::cout.imbue(std::locale("en_US.UTF-8"));
    std::cout << "american locale: " << std::showbase
              << std::put_money(12345678.0)<< '\n';

    std::cout.imbue(std::locale(std::cout.getloc(), new space_out));
    std::cout << "locale with modified moneypunct: "
              << std::put_money(12345678.0)<< '\n';
}

Output:

american locale: $123,456.78
locale with modified moneypunct: 12 34 56 78

See also

[virtual]
provides the numbers of digits between each pair of thousands separators
(virtual protected member function)