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std::num_put

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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.

cpp/locale/locale/facetstd-num put-inheritance.svg
About this image

Inheritance diagram

Contents

[edit] Type requirements

-
OutputIt must meet the requirements of OutputIterator.

[edit] 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.

[edit] Member types

Member type Definition
char_type CharT
iter_type OutputIt

[edit] 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)

[edit] Protected member functions

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

[edit] Member objects

static std::locale::id id
id of the locale
(public member object)

[edit] Example

#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

[edit] 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]
converts an integral or floating point value to wstring
(function) [edit]