std::num_put(3)

NAME
std::num_put - std::num_put

Synopsis
   Defined in header <locale>
   template<
       class CharT,
       class OutputIt = std::ostreambuf_iterator<CharT>
   > class num_put;
   Class std::num_put encapsulates the rules for formatting numeric values as strings.
   Specifically, the types bool, long, unsigned long
   , long long, unsigned long long
   (since C++11), double, long double, void*, and of all types implicitly convertible
   to these (such as int or float) are supported. The standard formatting output
   operators (such as cout << n;) use the std::num_put facet of the I/O stream's locale
   to generate text representation of numbers.
   std-num put-inheritance.svg
                        Inheritance diagram
   If a std::num_put specialization is not guaranteed to be provided by the standard
   library (see below), the behaviors of its put() and do_put() are not guaranteed as
   specified.

Specializations
   The standard library is guaranteed to provide the following specializations (they
   are required to be implemented by any locale object):
   Defined in header <locale>
   std::num_put<char> creates narrow string representations of numbers
   std::num_put<wchar_t> creates wide string representations of numbers
   In addition, the standard library is also guaranteed to provide every specialization
   that satisfies the following type requirements:
     * CharT is one of
          * char,
          * wchar_t, and
          * any other implementation-defined character container type that meets the
            requirements for a character on which any of the iostream components can be
            instantiated; and
     * OutputIt must meet the requirements of LegacyOutputIterator.

Member types
   Member type Definition
   char_type CharT
   iter_type OutputIt

Member functions
   constructor constructs a new num_put facet
                 (public member function)
   put invokes do_put
                 (public member function)

Protected member functions
   destructor destructs a num_put facet
                (protected member function)
   do_put formats a number and writes to output stream
   [virtual] (virtual protected member function)

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

Example
// Run this code
 #include <iostream>
 #include <iterator>
 #include <locale>
 #include <string>
 int main()
 {
     double n = 1234567.89;
     std::cout.imbue(std::locale("de_DE.UTF-8"));
     std::cout << "Direct conversion to string:\n"
               << std::to_string(n) << '\n'
               << "Output using a german locale:\n"
               << std::fixed << n << '\n'
               << "Output using an american locale:\n";
     // use the facet directly
     std::cout.imbue(std::locale("en_US.UTF-8"));
     auto& f = std::use_facet<std::num_put<char>>(std::cout.getloc());
     f.put(std::ostreambuf_iterator<char>(std::cout), std::cout, ' ', n);
     std::cout << '\n';
 }

Possible output:
 Direct conversion to string:
 1234567.890000
 Output using a german locale:
 1.234.567,890000
 Output using an american locale:
 1,234,567.890000
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                       num_put was guaranteed to accept any only guarantees to accept
                       CharT that char,
   LWG 427 C++98 meets the requirements for a wchar_t and other
                       character on which implementation-
                       any of the iostream components can defined character types
                       be instantiated
                        can guarantee to accept
   LWG 2392 C++98 only character type CharT could be implementation-
                       guaranteed to be accepted by num_put defined character container
                        types

See also
   numpunct defines numeric punctuation rules
              (class template)
   num_get parses numeric values from an input character sequence
              (class template)
   to_string converts an integral or floating-point value to string
   (C++11) (function)
   to_wstring converts an integral or floating-point value to wstring
   (C++11) (function)