WCSTOD(3P) POSIX Programmer's Manual WCSTOD(3P)PROLOG
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
These functions shall convert the initial portion of the wide-character
string pointed to by nptr to double, float, and long double representa‐
tion, respectively. First, they shall decompose the input wide-charac‐
ter 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 rep‐
resenting 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 option‐
ally 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 num‐
ber, 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 appropri‐
ate 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 (cate‐
gory 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 success‐
ful.
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 cor‐
rectly rounded. If the subject sequence D has the decimal form and more
than DECIMAL_DIG significant digits, consider the two bounding, adja‐
cent decimal strings L and U, both having DECIMAL_DIG significant dig‐
its, 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 round‐
ing 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 ALSOiswspace(), localeconv(), scanf(), setlocale(), wcstol(), the Base Def‐
initions volume of IEEE Std 1003.1-2001, Chapter 7, Locale, <float.h>,
<wchar.h>
COPYRIGHT
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 .
IEEE/The Open Group 2003 WCSTOD(3P)
