25 Localization library [localization]

25.4 Standard locale categories [locale.categories]

25.4.2 The numeric category [category.numeric]

25.4.2.1 Class template num_­get [locale.num.get]

namespace std {
  template <class charT, class InputIterator = istreambuf_iterator<charT>>
    class num_get : public locale::facet {
    public:
      using char_type = charT;
      using iter_type = InputIterator;

      explicit num_get(size_t refs = 0);

      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, bool& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, long long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned short& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned int& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned long long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, float& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, double& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, long double& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, void*& v) const;

      static locale::id id;

    protected:
      ~num_get();
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, bool& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, long long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned short& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned int& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned long long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, float& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, double& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, long double& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, void*& v) const;
    };
}
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The facet num_­get is used to parse numeric values from an input sequence such as an istream.

25.4.2.1.1 num_­get members [facet.num.get.members]

iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, bool& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned short& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned int& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, float& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, double& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long double& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, void*& val) const;
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Returns: do_­get(in, end, str, err, val).

25.4.2.1.2 num_­get virtual functions [facet.num.get.virtuals]

iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned short& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned int& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, float& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, double& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long double& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, void*& val) const;
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Effects: Reads characters from in, interpreting them according to str.flags(), use_­facet<ctype<​charT>>(loc), and use_­facet<numpunct<charT>>(loc), where loc is str.getloc().
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The details of this operation occur in three stages
  • (2.1)
    Stage 1: Determine a conversion specifier
  • (2.2)
    Stage 2: Extract characters from in and determine a corresponding char value for the format expected by the conversion specification determined in stage 1.
  • (2.3)
    Stage 3: Store results
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The details of the stages are presented below.
  • (3.1)
    Stage 1: The function initializes local variables via
    fmtflags flags = str.flags();
fmtflags basefield = (flags & ios_base::basefield);
fmtflags uppercase = (flags & ios_base::uppercase);
fmtflags boolalpha = (flags & ios_base::boolalpha);
    For conversion to an integral type, the function determines the integral conversion specifier as indicated in Table 68.
    The table is ordered.
    That is, the first line whose condition is true applies.
    Table 68 — Integer conversions
    State
    stdio equivalent
    basefield == oct
    %o
    basefield == hex
    %X
    basefield == 0
    %i
    signed integral type
    %d
    unsigned integral type
    %u
    For conversions to a floating type the specifier is %g.
    For conversions to void* the specifier is %p.
    A length modifier is added to the conversion specification, if needed, as indicated in Table 69.
    Table 69 — Length modifier
    Type
    Length modifier
    short
    h
    unsigned short
    h
    long
    l
    unsigned long
    l
    long long
    ll
    unsigned long long
    ll
    double
    l
    long double
    L
  • (3.2)
    Stage 2: If in == end then stage 2 terminates.
    Otherwise a charT is taken from in and local variables are initialized as if by
    char_type ct = *in;
char c = src[find(atoms, atoms + sizeof(src) - 1, ct) - atoms];
if (ct == use_facet<numpunct<charT>>(loc).decimal_point())
c = '.';
bool discard =
  ct == use_facet<numpunct<charT>>(loc).thousands_sep()
  && use_facet<numpunct<charT>>(loc).grouping().length() != 0;
    where the values src and atoms are defined as if by:
    static const char src[] = "0123456789abcdefxABCDEFX+-";
char_type atoms[sizeof(src)];
use_facet<ctype<charT>>(loc).widen(src, src + sizeof(src), atoms);
    for this value of loc.
    If discard is true, then if '.' has not yet been accumulated, then the position of the character is remembered, but the character is otherwise ignored.
    Otherwise, if '.' has already been accumulated, the character is discarded and Stage 2 terminates.
    If it is not discarded, then a check is made to determine if c is allowed as the next character of an input field of the conversion specifier returned by Stage 1.
    If so, it is accumulated.
    If the character is either discarded or accumulated then in is advanced by ++in and processing returns to the beginning of stage 2.
  • (3.3)
    Stage 3: The sequence of chars accumulated in stage 2 (the field) is converted to a numeric value by the rules of one of the functions declared in the header <cstdlib>:
    • (3.3.1)
      For a signed integer value, the function strtoll.
    • (3.3.2)
      For an unsigned integer value, the function strtoull.
    • (3.3.3)
      For a float value, the function strtof.
    • (3.3.4)
      For a double value, the function strtod.
    • (3.3.5)
      For a long double value, the function strtold.
    The numeric value to be stored can be one of:
    • (3.3.6)
      zero, if the conversion function does not convert the entire field.
    • (3.3.7)
      the most positive (or negative) representable value, if the field to be converted to a signed integer type represents a value too large positive (or negative) to be represented in val.
    • (3.3.8)
      the most positive representable value, if the field to be converted to an unsigned integer type represents a value that cannot be represented in val.
    • (3.3.9)
      the converted value, otherwise.
    The resultant numeric value is stored in val.
    If the conversion function does not convert the entire field, or if the field represents a value outside the range of representable values, ios_­base​::​failbit is assigned to err.
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Digit grouping is checked.
That is, the positions of discarded separators is examined for consistency with use_­facet<numpunct<charT>>(loc).grouping().
If they are not consistent then ios_­base​::​failbit is assigned to err.
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In any case, if stage 2 processing was terminated by the test for in == end then err |= ios_­base​::​eofbit is performed.
iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, bool& val) const;
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Effects: If (str.flags()&ios_­base​::​boolalpha) == 0 then input proceeds as it would for a long except that if a value is being stored into val, the value is determined according to the following: If the value to be stored is 0 then false is stored.
If the value is 1 then true is stored.
Otherwise true is stored and ios_­base​::​failbit is assigned to err.
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Otherwise target sequences are determined “as if” by calling the members falsename() and truename() of the facet obtained by use_­facet<numpunct<charT>>(str.getloc()).
Successive characters in the range [in, end) (see [sequence.reqmts]) are obtained and matched against corresponding positions in the target sequences only as necessary to identify a unique match.
The input iterator in is compared to end only when necessary to obtain a character.
If a target sequence is uniquely matched, val is set to the corresponding value.
Otherwise false is stored and ios_­base​::​failbit is assigned to err.
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The in iterator is always left pointing one position beyond the last character successfully matched.
If val is set, then err is set to str.goodbit; or to str.eofbit if, when seeking another character to match, it is found that (in == end).
If val is not set, then err is set to str.failbit; or to (str.failbit|str.eofbit) if the reason for the failure was that (in == end).
[ Example
:
For targets true: "a" and false: "abb", the input sequence "a" yields val == true and err == str.eofbit; the input sequence "abc" yields err = str.failbit, with in ending at the 'c' element.
For targets true: "1" and false: "0", the input sequence "1" yields val == true and err == str.goodbit.
For empty targets (""), any input sequence yields err == str.failbit.
— end example
 ]
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Returns: in.