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    std::num_put

    From cppreference.com
     
    C++
     
    Text processing library
     
    Localization library
     
    std::num_put
     
    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.

    Imagecpp/locale/locale/facet

    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:

    Nested types

    Type Definition
    char_type CharT
    iter_type OutputIt

    Data members

    Member Description
    std::locale::id id [static] the identifier of the facet

    Member functions

    		 constructs a new num_put facet
    (public member function)
    		invokes do_put
    (public member function)

    Protected member functions

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

    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
    LWG 427 C++98 num_put was guaranteed to accept any CharT that
    meets the requirements for a character on which
    any of the iostream components can be instantiated     		only guarantees to accept char,
    wchar_t and other implementation-
    defined character types
    LWG 2392 C++98 only character type CharT could be
    guaranteed to be accepted by num_put     		can guarantee to accept implementation-
    defined character container types

    See also

    		 defines numeric punctuation rules
    (class template) [edit]
    		parses numeric values from an input character sequence
    (class template) [edit]
    (C++11)
    		 converts an integral or floating-point value to string
    (function) [edit]
    (C++11)
    		 converts an integral or floating-point value to wstring
    (function) [edit]