std::num_get

 

C++

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Localizations library

Locales and facets
locale
use_facet	has_facet
Character classification
isspace isblank (C++11) iscntrl isupper islower isalpha	isdigit ispunct isxdigit isalnum isprint isgraph
Conversions
toupper tolower	wstring_convert (C++11) wbuffer_convert (C++11)
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
Facet categories
ctype ctype<char> codecvt collate messages time_get time_put	num_get num_put numpunct money_get money_put moneypunct
Locale-specific facets
ctype_byname ctype_byname<char> codecvt_byname messages_byname collate_byname	time_get_byname time_put_byname numpunct_byname moneypunct_byname
Code conversion facets
codecvt_utf8 (C++11) codecvt_utf16 (C++11)	codecvt_utf8_utf16 (C++11) codecvt_mode (C++11)
C locale
setlocale localeconv lconv	LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME

 

std::num_get

Member functions

num_get::num_get

num_get::~num_get

num_get::get num_get::do_get

 

Defined in header <locale>
template< class charT,           class InputIterator = std::istreambuf_iterator<charT> > class num_get : public std::locale::facet;

Class std::num_get encapsulates the rules for parsing string representations of values of type bool, unsigned short, unsigned int, long, unsigned long, long long, unsigned long long, float, double, long double, and void*. 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.

Two specializations and two partial specializations are provided by the standard library and are implemented by all locale objects created in a C++ program:

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, InputIterator>	creates narrow string parsing of numbers using custom input iterator
std::num_get<wchar_t, InputIterator>	creates wide string parsing of numbers using custom input iterator

Member types

Member type	Definition
char_type	charT
iter_type	InputIterator

Member objects

Member name	Type
id (static)	std::locale::id

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)

Protected member functions

do_get [virtual]	parses a number from an input stream (virtual protected member function)

Example

#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)