std::num_get(3)

NAME
std::num_get - std::num_get

Synopsis
   Defined in header <locale>
   template<
       class CharT,
       class InputIt = std::istreambuf_iterator<CharT>
   > class num_get;
   Class std::num_get encapsulates the rules for parsing string representations of
   numeric values. Specifically, types bool, unsigned short, unsigned int, long,
   unsigned long
   , long long, unsigned long long
   (since C++11), float, double, long double, and void* are supported. The standard
   formatting input operators (such as cin >> n;) use the std::num_get facet of the I/O
   stream's locale to parse the text representations of the numbers.
   std-num get-inheritance.svg
                        Inheritance diagram
   If a std::num_get specialization is not guaranteed to be provided by the standard
   library (see below), the behaviors of its get() and do_get() 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_get<char> creates narrow string parsing of numbers
   std::num_get<wchar_t> creates wide string parsing 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
     * InputIt must meet the requirements of LegacyInputIterator.

Member types
   Member type Definition
   char_type CharT
   iter_type InputIt

Member functions
   constructor constructs a new num_get facet
                 (public member function)
   get invokes do_get
                 (public member function)

Member objects
   static std::locale::id id id of the locale
                        (public member object)

Protected member functions
   destructor destructs a num_get facet
                (protected member function)
   do_get parses a number from an input stream
   [virtual] (virtual protected member function)

Example
// Run this code
 #include <iostream>
 #include <iterator>
 #include <locale>
 #include <sstream>
 #include <string>
 int main()
 {
     std::string de_double = "1.234.567,89";
     std::string us_double = "1,234,567.89";
     // parse using streams
     std::istringstream de_in(de_double);
     de_in.imbue(std::locale("de_DE.UTF-8"));
     double f1;
     de_in >> f1;
     std::istringstream us_in(de_double);
     us_in.imbue(std::locale("en_US.UTF-8"));
     double f2;
     us_in >> f2;
     std::cout << "Parsing " << de_double << " as double gives " << std::fixed
               << f1 << " in de_DE locale and " << f2 << " in en_US\n";
     // use the facet directly
     std::istringstream s3(us_double);
     s3.imbue(std::locale("en_US.UTF-8"));
     auto& f = std::use_facet<std::num_get<char>>(s3.getloc());
     std::istreambuf_iterator<char> beg(s3), end;
     double f3;
     std::ios::iostate err;
     f.get(beg, end, s3, err, f3);
     std::cout << "parsing " << us_double
               << " as double using raw en_US facet gives " << f3 << '\n';
 }

Output:
 Parsing 1.234.567,89 as double gives 1234567.890000 in de_DE locale and 1.234000 in en_US
 parsing 1,234,567.89 as double using raw en_US facet gives 1234567.890000
   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_get 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_get defined character container
                        types

See also
   numpunct defines numeric punctuation rules
              (class template)
   num_put formats numeric values for output as character sequence
              (class template)
   operator>> extracts formatted data
              (public member function of std::basic_istream<CharT,Traits>)