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.
wcstod, wcstof, wcstold — convert a wide-character string to a double-
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);
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 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 '+' 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
* A 0x or 0X, then a non-empty sequence of hexadecimal digits option‐
ally 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
* One of NAN or NAN(n-wchar-sequenceopt), or any other wide string
ignoring case in the NAN part, where:
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
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-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-
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 char‐
acter is not defined, the radix character shall default to a <period>
In other than the C or POSIX locales, other implementation-defined sub‐
ject 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
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.
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.
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 rounding direc‐
tion, with the extra stipulation that the error with respect to D
should have a correct sign for the current rounding direction.
SEE ALSOfscanf(), iswspace(), localeconv(), setlocale(), wcstol()
The Base Definitions volume of POSIX.1‐2008, Chapter 7, Locale,
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 Electri‐
cal 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
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IEEE/The Open Group 2013 WCSTOD(3P)