std::num_put

 

C++

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Technical specifications

Symbols index

External libraries

 

Localization library

Locales and facets
Locales
has_facet use_facet	locale
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
ctype facets
ctype ctype<char> ctype_byname	codecvt codecvt_byname
numeric facets
num_get num_put	numpunct numpunct_byname
collate facets
collate	collate_byname
time facets
time_get time_put	time_get_byname time_put_byname
monetary facets
money_get money_put	moneypunct moneypunct_byname
messages facets
messages	messages_byname

Character classification and conversion
Character classification
isspace isblank (C++11) iscntrl	isupper islower isalpha	ispunct isdigit isxdigit	isalnum isprint isgraph

Character conversions

toupper

tolower

String and stream conversions

wstring_convert (C++11/17/26*)

wbuffer_convert (C++11/17/26*)

Text encoding identifications

text_encoding (C++26)

Unicode conversion facets

codecvt_utf8 (C++11/17/26*)

codecvt_utf16 (C++11/17/26*)

codecvt_utf8_utf16 (C++11/17/26*)

codecvt_mode (C++11/17/26*)

C library locales
LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME	setlocale localeconv lconv

 

std::num_put

Member functions

num_put::num_put

num_put::~num_put

num_put::putnum_put::do_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(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.

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 [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 <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)