NAME¶

std::num_put - std::num_put

Synopsis¶

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.

std-num put-inheritance.svg

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.

Member types¶

Member type Definition
char_type CharT
iter_type OutputIt

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 formats a number and writes to output stream
[virtual] (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 <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
num_put was guaranteed to accept any only guarantees to accept
CharT that char,
LWG 427 C++98 meets the requirements for a wchar_t and other
character on which implementation-
any of the iostream components can defined character types
be instantiated
can guarantee to accept
LWG 2392 C++98 only character type CharT could be implementation-
guaranteed to be accepted by num_put 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 converts an integral or floating-point value to string
(C++11) (function)
to_wstring converts an integral or floating-point value to wstring
(C++11) (function)