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# std::numpunct

From cppreference.com
< cpp‎ | locale

Defined in header `<locale>` |  |
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-sep`s (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

Two standalone (locale-independent) specializations are provided by the standard library:

Defined in header `<locale>`
std::numpunct<char> | provides equivalents of the "C" locale preferences
std::numpunct<wchar_t> | provides wide character equivalents of the "C" locale preferences

In addition, every locale object constructed in a C++ program implements its own (locale-specific) versions of these specializations.

### [edit] Member types

Member type | Definition
`char_type` | `charT`
`string_type` | std::basic_string<charT>

### [edit] Member functions

(constructor) | constructs a new numpunct facet (public member function) [edit]
(destructor) | destructs a numpunct facet (protected member function) [edit]
#####
decimal_point | invokes `do_decimal_point` (public member function) [edit]
thousands_sep | invokes `do_thousands_sep` (public member function) [edit]
grouping | invokes `do_grouping` (public member function) [edit]
truenamefalsename | invokes `do_truename` or `do_falsename` (public member function) [edit]

### [edit] Protected member functions

do_decimal_point [virtual] | provides the character to use as decimal point (virtual protected member function) [edit]
do_thousands_sep [virtual] | provides the character to use as thousands separator (virtual protected member function) [edit]
do_grouping [virtual] | provides the numbers of digits between each pair of thousands separators (virtual protected member function) [edit]
do_truenamedo_falsename [virtual] | provides the string to use as the name of the boolean true and false (virtual protected member function) [edit]

### [edit] Member objects

static std::locale::id id | id of the locale (public member object)

### [edit] Example

The following example changes the string representations of true and false

Run this code

    #include <iostream>
    #include <locale>

    struct french_bool : std::numpunct<char> {
        string_type do_truename() const { return "oui"; }
        string_type do_falsename() const { return "non"; }
    };

    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: oui, non

### [edit] See also

numpunct_byname | creates a numpunct facet for the named locale (class template)

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