std::num_get

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Defined in header <locale>

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template< class charT,

          class InputIterator = std::istreambuf_iterator<charT>

> class num_get : public std::locale::facet;

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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:

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Member types

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Member objects

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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

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

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