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, 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

Type requirements

-

OutputIt must meet the requirements of LegacyOutputIterator.

Specializations

Two standalone (locale-independent) full specializations and two partial specializations are provided by the standard library:

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
std::num_put<char, OutputIt>	creates narrow string representations of numbers using custom output iterator
std::num_put<wchar_t, OutputIt>	creates wide string representations of numbers using custom output iterator

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`
`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"));
    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';
}

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

Language
Standard Library Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

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)