std::numpunct<CharT>::grouping, std::numpunct<CharT>::do_grouping

public:
std::string grouping() const;

protected:
virtual std::string do_grouping() const;

This function returns a string, vec, which is used as a vector of integer values. (For example, "\003" specifies groups of 3 digits each, while "3" implies groups of 51 digits each.). Each element vec[i] represents the number of digits in the ith digit group of the integer part of the number, counting from the right: vec[0] holds the number of digits in the rightmost group, vec[1] - in the second group from the right, etc. The grouping indicated by the last character, vec[vec.size()-1], is repeatedly reused to group all remaining digits in the (left part of) the number. If vec[i] is non-positive or equals CHAR_MAX the size of the corresponding digit group is unlimited.

Return value

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

Example

#include <iostream>
#include <limits>
#include <locale>
 
struct space_out : std::numpunct<char>
{
    char do_thousands_sep()   const { return ' ';  } // separate with spaces
    std::string do_grouping() const { return "\1"; } // groups of 1 digit
};
 
struct g123 : std::numpunct<char>
{
    std::string do_grouping() const { return "\1\2\3"; }
};
 
int main()
{
    std::cout << "Default locale: " << 12345678 << '\n';
    std::cout.imbue(std::locale(std::cout.getloc(), new space_out));
    std::cout << "Locale with modified numpunct: " << 12345678 << '\n';
    std::cout.imbue(std::locale(std::cout.getloc(), new g123));
    std::cout << "Locale with \\1\\2\\3 grouping: "
              << std::numeric_limits<unsigned long long>::max() << '\n'
              << "Same, for a floating-point number: "
              << std::fixed << 123456789.123456789 << '\n';
}

Default locale: 12345678
Locale with modified numpunct: 1 2 3 4 5 6 7 8
Locale with \1\2\3 grouping: 18,446,744,073,709,551,61,5
Same, for a floating-point number: 123,456,78,9.123457

See also