# std::num_put

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< cpp‎ | locale

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 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.

### 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

(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 [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

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)

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