WCSTOD
Section: POSIX Programmer's Manual (3P)
Updated: 2013
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This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
wcstod,
wcstof,
wcstold
--- convert a wide-character string to a double-precision number
SYNOPSIS
#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);
DESCRIPTION
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here and the
ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.
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
'+'
or
'-'
sign, then one of the following:
- *
-
A non-empty sequence of decimal digits optionally containing a radix
character; then an optional exponent part consisting of the wide
character
'e'
or the wide character
'E',
optionally followed by a
'+'
or
'-'
wide character, and then followed by one or more decimal digits
- *
-
A 0x or 0X, then a non-empty sequence of hexadecimal digits optionally
containing a radix character; then an optional binary exponent part
consisting of the wide character
'p'
or the wide character
'P',
optionally followed by a
'+'
or
'-'
wide character, and then followed by one or more decimal digits
- *
-
One of INF or INFINITY, or any other wide string equivalent except for
case
- *
-
One of NAN or NAN(n-wchar-sequenceopt), 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-sequenceopt) 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 current 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.
These functions 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.
RETURN VALUE
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].
ERRORS
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.
EXAMPLES
None.
APPLICATION USAGE
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
dqL<=
D<=
Udq.
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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
fscanf(),
iswspace(),
localeconv(),
setlocale(),
wcstol()
The Base Definitions volume of POSIX.1-2008,
Chapter 7,
Locale,
<float.h>,
<wchar.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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