25 Localization library [localization]

25.4 Standard locale categories [locale.categories]

25.4.3 The numeric punctuation facet [facet.numpunct]

25.4.3.1 Class template numpunct [locale.numpunct]

25.4.3.1.2 numpunct virtual functions [facet.numpunct.virtuals]

char_type do_decimal_point() const;
1
#
Returns: A character for use as the decimal radix separator.
The required specializations return '.' or L'.'.
char_type do_thousands_sep() const;
2
#
Returns: A character for use as the digit group separator.
The required specializations return ',' or L','.
string do_grouping() const;
3
#
Returns: A basic_string<char> vec used as a vector of integer values, in which each element vec[i] represents the number of digits241 in the group at position i, starting with position 0 as the rightmost group.
If vec.size() <= i, the number is the same as group (i - 1); if (i < 0 || vec[i] <= 0 || vec[i] == CHAR_­MAX), the size of the digit group is unlimited.
4
#
The required specializations return the empty string, indicating no grouping.
string_type do_truename() const; string_type do_falsename() const;
5
#
Returns: A string representing the name of the boolean value true or false, respectively.
6
#
In the base class implementation these names are "true" and "false", or L"true" and L"false".
241)
Thus, the string "\003" specifies groups of 3 digits each, and "3" probably indicates groups of 51 (!) digits each, because 51 is the ASCII value of "3".