num_get::get

Artikel
07/11/2012

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;
}

Output

.
money_get( ) = -1000.56

Requirements

Header: <locale>

Namespace: std

Bagikan melalui