Section
std::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.
# Declarations
template<
class CharT,
class OutputIt = std::ostreambuf_iterator<CharT>
> class num_put;
# 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';
}
# Defect reports
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 427 | C++98 | num_put was guaranteed to accept any CharT thatmeets the requirements for a character on whichany 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 | can guarantee to accept implementation-defined character container types |