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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../locale/numpunct.html below:

std::numpunct - cppreference.com

template< class CharT > class numpunct;

The facet std::numpunct encapsulates numeric punctuation preferences. Stream I/O operations use std::numpunct through std::num_get and std::num_put for parsing numeric input and formatting numeric output.

The numbers that are supported by std::numpunct have the format described below. Here digit represents the radix set specified by the fmtflags argument value, thousands-sep and decimal-point are the results of thousands_sep() and decimal_point() functions respectively.

The format of integer values is as follows:

integer     ::= [sign] units
sign        ::= plusminus
plusminus   ::= '+' | '-'
units       ::= digits [thousands-sep units]
digits      ::= digit [digits]

The number of digits between the thousand-seps (maximum size of digits) is specified by the result of grouping().

The format of floating-point values is as follows:

floatval    ::= [sign] units [decimal-point [digits]] [e [sign] digits] |
                [sign]        decimal-point  digits   [e [sign] digits]
e           ::= 'e' | 'E'

Inheritance diagram

[edit] Specializations

The standard library is guaranteed to provide the following specializations (they are required to be implemented by any locale object):

std::numpunct<char> provides equivalents of the "C" locale preferences std::numpunct<wchar_t> provides wide character equivalents of the "C" locale preferences [edit] Nested types [edit] Data members [edit] Member functions [edit] Protected member functions provides the character to use as decimal point
(virtual protected member function) [edit] provides the character to use as thousands separator
(virtual protected member function) [edit] provides the numbers of digits between each pair of thousands separators
(virtual protected member function) [edit] provides the string to use as the name of the boolean true and false
(virtual protected member function) [edit] [edit] Example

The following example changes the string representations of true and false:

#include <iostream>
#include <locale>
 
struct french_bool : std::numpunct<char>
{
    string_type do_truename() const override { return "vrai"; }
    string_type do_falsename() const override { return "faux"; }
};
 
int main()
{
    std::cout << "default locale: "
              << std::boolalpha << true << ", " << false << '\n';
    std::cout.imbue(std::locale(std::cout.getloc(), new french_bool));
    std::cout << "locale with modified numpunct: "
              << std::boolalpha << true << ", " << false << '\n';
}

Output:

default locale: true, false
locale with modified numpunct: vrai, faux

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior LWG 338 C++98 the sign token allowed an optional whitespace following + or - removed the whitespace [edit] See also creates a numpunct facet for the named locale
(class template)

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