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.

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 ):

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 .

Nested types

Data members

Member functions

Protected member functions

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';
}

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.

See also