25 Localization library [localization]

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().

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

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 73. The table is ordered. That is, the first line whose condition is true applies.

  Table 73 — 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 74.

  Table 74 — 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.

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.

In any case, if stage 2 processing was terminated by the test for in == end then err |= ios_­base​::​eofbit is performed.

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.

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.

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 ]

Returns: in.