std::numpunct::grouping, std::numpunct::do_grouping

C++

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Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

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Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

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Technical Specifications

Localizations library

Locales and facets
locale
use_facet	has_facet
Character classification
isspace isblank (C++11) iscntrl isupper islower isalpha	isdigit ispunct isxdigit isalnum isprint isgraph
Conversions
toupper tolower	wstring_convert (C++11) wbuffer_convert (C++11)
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
Facet categories
ctype ctype<char> codecvt collate messages time_get time_put	num_get num_put numpunct money_get money_put moneypunct
Locale-specific facets
ctype_byname codecvt_byname messages_byname collate_byname	time_get_byname time_put_byname numpunct_byname moneypunct_byname
Code conversion facets
codecvt_utf8 (C++11) codecvt_utf16 (C++11)	codecvt_utf8_utf16 (C++11) codecvt_mode (C++11)
C locale
setlocale localeconv lconv	LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME

std::numpunct

Member functions

numpunct::numpunct

numpunct::~numpunct

numpunct::decimal_pointnumpunct::do_decimal_point

numpunct::thousands_sepnumpunct::do_thousands_sep

numpunct::groupingnumpunct::do_grouping

numpunct::truenamenumpunct::do_truenamenumpunct::falsenamenumpunct::do_falsename

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<<)

The groups are stored as binary values: three-digit group is '\3', and 51-digit group is '3'. The character at index zero of the returned string holds the number of digits in the rightmost group. The character at index 1 holds the number of digits in the second group from the right, etc. The grouping indicated by the last character in the returned string is reused to group all remaining digits in the (left part of) the number.

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';
}

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

See also

do_thousands_sep [virtual]

provides the character to use as thousands separator (virtual protected member function)