std::num_put
Defined in header <locale>
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template< class CharT, |
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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.
Contents |
[edit] 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.
[edit] Nested types
Type | Definition |
char_type
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CharT
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iter_type
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OutputIt
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[edit] Data members
Member | Description |
std::locale::id id [static]
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the identifier of the facet |
[edit] Member functions
constructs a new num_put facet (public member function) | |
invokes do_put (public member function) |
[edit] Protected member functions
destructs a num_put facet (protected member function) | |
[virtual] |
formats a number and writes to output stream (virtual protected member function) |
[edit] Example
#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
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
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LWG 427 | C++98 | num_put was guaranteed to accept any CharT thatmeets 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 beguaranteed to be accepted by num_put
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can guarantee to accept implementation- defined character container types |
[edit] See also
defines numeric punctuation rules (class template) | |
parses numeric values from an input character sequence (class template) | |
(C++11) |
converts an integral or floating-point value to string (function) |
(C++11) |
converts an integral or floating-point value to wstring (function) |