30 Localization library [localization]

30.4 Standard locale categories [locale.categories]

30.4.4 The numeric punctuation facet [facet.numpunct]

30.4.4.1 Class template numpunct [locale.numpunct]

30.4.4.1.3 Virtual functions [facet.numpunct.virtuals]

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char_type do_decimal_point() const;
1
#
Returns: A character for use as the decimal radix separator.
The required specializations return '.' or L'.'.
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char_type do_thousands_sep() const;
2
#
Returns: A character for use as the digit group separator.
The required specializations return ',' or L','.
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string do_grouping() const;
3
#
Returns: A string vec used as a vector of integer values, in which each element vec[i] represents the number of digits252 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.
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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".
252)252)
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".