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
(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 specializations (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 retroactively 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 character 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 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::basic_istream<CharT,Traits>)