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

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< cpp‎ | locale‎ | numpunct

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 an std::string holding, in each char element, the number of digits in each group of the numeric output formatted by `num_put::put()` (and, therefore, `basic_ostream::operator<<`).

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 `i`th 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

Run this code

    #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';
    }

Output:

    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

do_thousands_sep [virtual] | provides the character to use as thousands separator (virtual protected member function)

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