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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 repre- sentations 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 special- izations (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 retroac- tively to previously published C++ standards. DR Applied to Behavior as published Cor- rect behavior num_get was guaranteed to accept any only guar- antees to accept CharT that char, LWG 427 C++98 meets the requirements for a wchar_t and other character on which implementa- tion- any of the iostream components can defined character types be instantiated can guaran- tee to accept LWG 2392 C++98 only character type CharT could be implementa- tion- 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::ba- sic_istream<CharT,Traits>) http://cppreference.com 2024.06.10 std::num_get(3)
NAME | Synopsis | Specializations | Member types | Member functions | Member objects | Protected member functions | Example | Output: | See also
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