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, 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

Type requirements
   -
   InputIt must meet the requirements of LegacyInputIterator.

Specializations
   Two standalone (locale-independent) full specializations and two partial
   specializations are provided by the standard library:
   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
   std::num_get<char, InputIt> creates narrow string parsing of numbers using custom
                        input iterator
   std::num_get<wchar_t, InputIt> creates wide string parsing of numbers using custom
                        input iterator
   In addition, every locale object constructed in a C++ program implements its own
   (locale-specific) versions of these specializations.

Member types
   Member type Definition
   char_type CharT
   iter_type InputIt

Member functions
   constructor constructs a new num_get facet
                 (public member function)
   destructor destructs a num_get facet
                 (protected 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
   do_get parses a number from an input stream
   [virtual] (virtual protected member function)

Example
// Run this code
 #include <iostream>
 #include <locale>
 #include <string>
 #include <sstream>
 #include <iterator>
 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"));
     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

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>)