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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 "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.
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 .