Originální popis anglicky:
wcstod, wcstof, wcstold - convert a wide-character string to a double-precision
number
Návod, kniha: POSIX Programmer's Manual
#include <wchar.h>
double wcstod(const wchar_t *restrict
nptr, wchar_t
**restrict endptr);
float wcstof(const wchar_t *restrict
nptr, wchar_t
**restrict endptr);
long double wcstold(const wchar_t *restrict
nptr,
wchar_t **restrict
endptr );
These functions shall convert the initial portion of the wide-character string
pointed to by
nptr to
double,
float, and
long
double representation, respectively. First, they shall decompose the input
wide-character string into three parts:
- 1.
- An initial, possibly empty, sequence of white-space
wide-character codes (as specified by iswspace())
- 2.
- A subject sequence interpreted as a floating-point constant
or representing infinity or NaN
- 3.
- A final wide-character string of one or more unrecognized
wide-character codes, including the terminating null wide-character code
of the input wide-character string
Then they shall attempt to convert the subject sequence to a floating-point
number, and return the result.
The expected form of the subject sequence is an optional plus or minus sign,
then one of the following:
- *
- A non-empty sequence of decimal digits optionally
containing a radix character, then an optional exponent part
- *
- A 0x or 0X, then a non-empty sequence of hexadecimal digits
optionally containing a radix character, then an optional binary exponent
part
- *
- One of INF or INFINITY, or any other wide string equivalent
except for case
- *
- One of NAN or NAN(n-wchar-sequence_opt), or any
other wide string ignoring case in the NAN part, where:
n-wchar-sequence:
digit
nondigit
n-wchar-sequence digit
n-wchar-sequence nondigit
The subject sequence is defined as the longest initial subsequence of the input
wide string, starting with the first non-white-space wide character, that is
of the expected form. The subject sequence contains no wide characters if the
input wide string is not of the expected form.
If the subject sequence has the expected form for a floating-point number, the
sequence of wide characters starting with the first digit or the radix
character (whichever occurs first) shall be interpreted as a floating constant
according to the rules of the C language, except that the radix character
shall be used in place of a period, and that if neither an exponent part nor a
radix character appears in a decimal floating-point number, or if a binary
exponent part does not appear in a hexadecimal floating-point number, an
exponent part of the appropriate type with value zero shall be assumed to
follow the last digit in the string. If the subject sequence begins with a
minus sign, the sequence shall be interpreted as negated. A wide-character
sequence INF or INFINITY shall be interpreted as an infinity, if representable
in the return type, else as if it were a floating constant that is too large
for the range of the return type. A wide-character sequence NAN or NAN(
n-wchar-sequence_opt) shall be interpreted as a quiet NaN, if supported
in the return type, else as if it were a subject sequence part that does not
have the expected form; the meaning of the
n-wchar sequences is
implementation-defined. A pointer to the final wide string shall be stored in
the object pointed to by
endptr, provided that
endptr is not a
null pointer.
If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2,
the conversion shall be rounded in an implementation-defined manner.
The radix character shall be as defined in the program's locale (category
LC_NUMERIC ). In the POSIX locale, or in a locale where the radix
character is not defined, the radix character shall default to a period (
'.' ).
In other than the C or POSIX locales, other implementation-defined
subject sequences may be accepted.
If the subject sequence is empty or does not have the expected form, no
conversion shall be performed; the value of
nptr shall be stored in the
object pointed to by
endptr, provided that
endptr is not a null
pointer.
The
wcstod() function shall not change the setting of
errno if
successful.
Since 0 is returned on error and is also a valid return on success, an
application wishing to check for error situations should set
errno to
0, then call
wcstod(),
wcstof(), or
wcstold(), then check
errno.
Upon successful completion, these functions shall return the converted value. If
no conversion could be performed, 0 shall be returned and
errno
may be set to [EINVAL].
If the correct value is outside the range of representable values,
±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL shall be returned
(according to the sign of the value), and
errno shall be set to
[ERANGE].
If the correct value would cause underflow, a value whose magnitude is no
greater than the smallest normalized positive number in the return type shall
be returned and
errno set to [ERANGE].
The
wcstod() function shall fail if:
- ERANGE
- The value to be returned would cause overflow or underflow.
The
wcstod() function may fail if:
- EINVAL
- No conversion could be performed.
The following sections are informative.
None.
If the subject sequence has the hexadecimal form and FLT_RADIX is not a power of
2, and the result is not exactly representable, the result should be one of
the two numbers in the appropriate internal format that are adjacent to the
hexadecimal floating source value, with the extra stipulation that the error
should have a correct sign for the current rounding direction.
If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
<float.h>) significant digits, the result should be correctly
rounded. If the subject sequence
D has the decimal form and more than
DECIMAL_DIG significant digits, consider the two bounding, adjacent decimal
strings
L and
U, both having DECIMAL_DIG significant digits,
such that the values of
L,
D, and
U satisfy
"L
<= D <= U" . The result should be one of the (equal or
adjacent) values that would be obtained by correctly rounding
L and
U according to the current rounding direction, with the extra
stipulation that the error with respect to
D should have a correct sign
for the current rounding direction.
None.
None.
iswspace() ,
localeconv() ,
scanf() ,
setlocale() ,
wcstol() , the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 7, Locale,
<float.h>,
<wchar.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
