home | help 
std::num_get(3) 	       C++ Standard Libary		 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 representa-
     tions 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 specializa-
     tions (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  com-
     ponents 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 retroac-
     tively 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 charac-
     ter 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 charac-
     ter 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>)

http://cppreference.com 	   2024.06.10			 std::num_get(3)
home | help