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.

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 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)
(destructor)	destructs a `num_put` facet (protected member function)
put	invokes `do_put` (public member function)

Protected member functions

do_put

[virtual]

formats a number and writes to output stream
(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 <locale>
#include <string>
#include <iterator>
 
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` could 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 and wchar_t, other types are implementation-defined

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Ranges library (C++20)
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Filesystem library (C++17)
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Technical specifications
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External libraries

Member functions
num_put::num_put
num_put::~num_put
num_put::putnum_put::do_put

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