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std::moneypunct<CharT,International>:: grouping, do_grouping

From cppreference.net
C++
Text processing library
Localization library
std::moneypunct
Defined in header <locale>
public :
std:: string grouping ( ) const ;
(1)
protected :
virtual std:: string do_grouping ( ) const ;
(2)
1) Public member function, calls the member function do_grouping of the most derived class.
2) Returns the pattern that determines the grouping of the digits in the monetary output, with the same exact meaning as std::numpunct::do_grouping .

Return value

The object of type std::string holding the groups. The standard specializations of std::moneypunct return an empty string, indicating no grouping. Typical groupings (e.g. the en_US locale) return " \003 " .

Example

Run this code 
#include <iomanip>
#include <iostream>
#include <iterator>
#include <locale>
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 character to use as thousands separator
(virtual protected member function)
[virtual]
provides the character to use as decimal point
(virtual protected member function)