std::numpunct (3) - Linux Manuals

std::numpunct: std::numpunct


std::numpunct - std::numpunct


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-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
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.

Member types

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

Member functions

              constructs a new numpunct facet
constructor (public member function)
              destructs a numpunct facet
destructor (protected member function)
              invokes do_decimal_point
decimal_point (public member function)
              invokes do_thousands_sep
thousands_sep (public member function)
              invokes do_grouping
grouping (public member function)
              invokes do_truename or do_falsename
truename (public member function)

Protected member functions

do_decimal_point provides the character to use as decimal point
                 (virtual protected member function)

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

do_grouping provides the numbers of digits between each pair of thousands separators
                 (virtual protected member function)

do_truename provides the string to use as the name of the boolean true and false
do_falsename (virtual protected member function)


Member objects

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


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';


  default locale: true, false
  locale with modified numpunct: oui, non

See also

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