Defined in header <locale>
    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.

cpp/locale/locale/facetstd-num put-inheritance.svg

Inheritance diagram.

Type requirements

-OutputIt must meet the requirements of LegacyOutputIterator.


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

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

Protected member functions

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)


#include <iostream>
#include <locale>
#include <string>
#include <iterator>
int main()
    double n = 1234567.89;
    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
    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';


Direct conversion to string:
Output using a german locale:
Output using an american locale:

See also

defines numeric punctuation rules
(class template)
parses numeric values from an input character sequence
(class template)
converts an integral or floating point value to string
converts an integral or floating point value to wstring

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