Edit

Share via

num_get Class

  • Article

A class template that describes an object that can serve as a locale facet to control conversions of sequences of type CharType to numeric values.

Syntax

template <class CharType, class InputIterator = istreambuf_iterator<CharType>>
class num_get : public locale::facet;

Parameters

CharType
The type used within a program to encode characters in a locale.

InputIterator
The type of iterator from which the numeric get functions read their input.

Remarks

As with any locale facet, the static object ID has an initial stored value of zero. The first attempt to access its stored value stores a unique positive value in id.

Constructors

Constructor Description
num_get The constructor for objects of type num_get that are used to extract numerical values from sequences.

Typedefs

Type name Description
char_type A type that is used to describe a character used by a locale.
iter_type A type that describes an input iterator.

Member functions

Member function Description
do_get A virtual function that is called to extracts a numerical or Boolean value from a character sequence.
get Extracts a numerical or Boolean value from a character sequence.

Requirements

Header: <locale>

Namespace: std

num_get::char_type

A type that is used to describe a character used by a locale.

typedef CharType char_type;

Remarks

The type is a synonym for the template parameter CharType.

num_get::do_get

A virtual function that is called to extracts a numerical or Boolean value from a character sequence.

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned short& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned int& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned long& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long long& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned long long& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    float& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    double& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long double& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    void *& val) const;

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    bool& val) const;

Parameters

first
The beginning of the range of characters from which to read the number.

last
The end of the range of characters from which to read the number.

iosbase
The ios_base whose flags are used by the conversion.

state
The state to which failbit (see ios_base::iostate) is added upon failure.

val
The value that was read.

Return Value

The iterator after the value has been read.

Remarks

The first virtual protected member function,

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long& val) const;

matches sequential elements beginning at first in the sequence [first, last) until it has recognized a complete, nonempty integer input field. If successful, it converts this field to its equivalent value as type long, and stores the result in val. It returns an iterator designating the first element beyond the numeric input field. Otherwise, the function stores nothing in val and sets ios_base::failbit in state. It returns an iterator designating the first element beyond any prefix of a valid integer input field. In either case, if the return value equals last, the function sets ios_base::eofbit in state.

The integer input field is converted by the same rules used by the scan functions for matching and converting a series of char elements from a file. (Each such char element is assumed to map to an equivalent element of type Elem by a simple, one-to-one, mapping.) The equivalent scan conversion specification is determined as follows:

If iosbase.ios_base::flags() & ios_base::basefield == ios_base::oct, the conversion specification is lo.

If iosbase.flags() & ios_base::basefield == ios_base::hex, the conversion specification is lx.

If iosbase.flags() & ios_base::basefield == 0, the conversion specification is li.

Otherwise, the conversion specification is ld.

The format of an integer input field is further determined by the locale facetfac returned by the call use_facet <numpunct<Elem>(iosbase.ios_base::getloc()). Specifically:

fac.numpunct::grouping() determines how digits are grouped to the left of any decimal point

fac.numpunct::thousands_sep() determines the sequence that separates groups of digits to the left of any decimal point.

If no instances of fac.thousands_sep() occur in the numeric input field, no grouping constraint is imposed. Otherwise, any grouping constraints imposed by fac.grouping() are enforced and separators are removed before the scan conversion occurs.

The fourth virtual protected member function:

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned long& val) const;

behaves the same as the first, except that it replaces a conversion specification of ld with lu. If successful it converts the numeric input field to a value of type unsigned long and stores that value in val.

The fifth virtual protected member function:

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long long& val) const;

behaves the same as the first, except that it replaces a conversion specification of ld with lld. If successful it converts the numeric input field to a value of type long long and stores that value in val.

The sixth virtual protected member function:

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned long long& val) const;

behaves the same as the first, except that it replaces a conversion specification of ld with llu. If successful it converts the numeric input field to a value of type unsigned long long and stores that value in val.

The seventh virtual protected member function:

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    float& val) const;

behaves the same as the first, except that it endeavors to match a complete, nonempty floating-point input field. fac.numpunct::decimal_point() determines the sequence that separates the integer digits from the fraction digits. The equivalent scan conversion specifier is lf.

The eighth virtual protected member function:

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    double& val) const;

behaves the same as the first, except that it endeavors to match a complete, nonempty floating-point input field. fac.numpunct::decimal_point() determines the sequence that separates the integer digits from the fraction digits. The equivalent scan conversion specifier is lf.

The ninth virtual protected member function:

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long double& val) const;

behaves the same as the eighth, except that the equivalent scan conversion specifier is Lf.

The tenth virtual protected member function:

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    void *& val) const;

behaves the same the first, except that the equivalent scan conversion specifier is p.

The last (eleventh) virtual protected member function:

virtual iter_type do_get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    bool& val) const;

behaves the same as the first, except that it endeavors to match a complete, nonempty Boolean input field. If successful it converts the Boolean input field to a value of type bool and stores that value in val.

A Boolean input field takes one of two forms. If iosbase.flags() & ios_base::boolalpha is false, it is the same as an integer input field, except that the converted value must be either 0 (for false) or 1 (for true). Otherwise, the sequence must match either fac.numpunct::falsename() (for false), or fac.numpunct::truename() (for true).

Example

See the example for get, where the virtual member function is called by do_get.

num_get::get

Extracts a numerical or Boolean value from a character sequence.

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    bool& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned short& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned int& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned long& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long long& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned long long& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    float& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    double& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long double& val) const;

iter_type get(
    iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    void *& val) const;

Parameters

first
The beginning of the range of characters from which to read the number.

last
The end of the range of characters from which to read the number.

iosbase
The ios_base whose flags are used by the conversion.

state
The state to which failbit (see ios_base::iostate) is added upon failure.

val
The value that was read.

Return Value

The iterator after the value has been read.

Remarks

All member functions return do_get( first, last, iosbase, state, val).

The first virtual protected member function tries to match sequential elements beginning at first in the sequence [ first, last) until it has recognized a complete, nonempty integer input field. If successful, it converts this field to its equivalent value as type long and stores the result in val. It returns an iterator designating the first element beyond the numeric input field. Otherwise, the function stores nothing in val and sets ios_base::failbit in state. It returns an iterator designating the first element beyond any prefix of a valid integer input field. In either case, if the return value equals last, the function sets ios_base::eofbit in state.

The integer input field is converted by the same rules used by the scan functions for matching and converting a series of char elements from a file. Each such char element is assumed to map to an equivalent element of type CharType by a simple, one-to-one mapping. The equivalent scan conversion specification is determined as follows:

  • If iosbase.flags& ios_base::basefield == ios_base::oct, the conversion specification is lo.

  • If iosbase.flags & ios_base::basefield == ios_base::hex, the conversion specification is lx.

  • If iosbase.flags & ios_base::basefield == 0, the conversion specification is li.

  • Otherwise, the conversion specification is ld.

The format of an integer input field is further determined by the locale facet fac returned by the call use_facet<numpunct<Elem>(iosbase.getloc()). Specifically:

  • fac.grouping determines how digits are grouped to the left of any decimal point.

  • fac.thousands_sep determines the sequence that separates groups of digits to the left of any decimal point.

If no instances of fac.thousands_sep occur in the numeric input field, no grouping constraint is imposed. Otherwise, any grouping constraints imposed by fac.grouping is enforced and separators are removed before the scan conversion occurs.

The second virtual protected member function:

virtual iter_type do_get(iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    unsigned long& val) const;

behaves the same as the first, except that it replaces a conversion specification of ld with lu. If successful, it converts the numeric input field to a value of type unsigned long and stores that value in val.

The third virtual protected member function:

virtual iter_type do_get(iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    double& val) const;

behaves the same as the first, except that it tries to match a complete, nonempty floating-point input field. fac.decimal_point determines the sequence that separates the integer digits from the fraction digits. The equivalent scan conversion specifier is lf.

The fourth virtual protected member function:

virtual iter_type do_get(iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    long double& val) const;

behaves the same the third, except that the equivalent scan conversion specifier is Lf.

The fifth virtual protected member function:

virtual iter_type do_get(iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    void *& val) const;

behaves the same the first, except that the equivalent scan conversion specifier is p.

The sixth virtual protected member function:

virtual iter_type do_get(iter_type first,
    iter_type last,
    ios_base& iosbase,
    ios_base::iostate& state,
    bool& val) const;

behaves the same as the first, except that it tries to match a complete, nonempty boolean input field. If successful it converts the Boolean input field to a value of type bool and stores that value in val.

A boolean input field takes one of two forms. If iosbase.flags & ios_base::boolalpha is false, it is the same as an integer input field, except that the converted value must be either 0 (for false) or 1 (for true). Otherwise, the sequence must match either fac.falsename (for false), or fac.truename (for true).

Example

// num_get_get.cpp
// compile with: /EHsc
#include <locale>
#include <iostream>
#include <sstream>
using namespace std;
int main( )
{
   locale loc( "german_germany" );

   basic_stringstream<char> psz, psz2;
   psz << "-1000,56";

   ios_base::iostate st = 0;
   long double fVal;
   cout << use_facet <numpunct <char> >(loc).thousands_sep( ) << endl;

   psz.imbue( loc );
   use_facet <num_get <char> >
   (loc).get( basic_istream<char>::_Iter( psz.rdbuf( ) ),
           basic_istream<char>::_Iter(0), psz, st, fVal );

   if ( st & ios_base::failbit )
      cout << "money_get( ) FAILED" << endl;
   else
      cout << "money_get( ) = " << fVal << endl;
}

num_get::iter_type

A type that describes an input iterator.

typedef InputIterator iter_type;

Remarks

The type is a synonym for the template parameter InputIterator.

num_get::num_get

The constructor for objects of type num_get that are used to extract numerical values from sequences.

explicit num_get(size_t refs = 0);

Parameters

refs
Integer value used to specify the type of memory management for the object.

Remarks

The possible values for the refs parameter and their significance are:

  • 0: The lifetime of the object is managed by the locales that contain it.

  • 1: The lifetime of the object must be manually managed.

  • > 1: These values are not defined.

No direct examples are possible, because the destructor is protected.

The constructor initializes its base object with locale::facet(refs).

See also

<locale>
facet Class
Thread Safety in the C++ Standard Library