WCSTOD(3C) Standard C Library Functions WCSTOD(3C)


wcstod, wcstof, wcstold, wstod, watof - convert wide character string to
floating-point number


#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);

double wstod(const wchar_t *nptr, wchar_t **endptr);

double watof(wchar_t *nptr);


The wcstod(), wcstof(), and wcstold() functions convert the initial
portion of the wide-character string pointed to by nptr to double, float,
and long double representation, respectively. They first 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(3C))

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 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:

o A non-empty sequence of decimal digits optionally containing a
radix character, then an optional exponent part

o A 0x or 0X, then a non-empty sequence of hexadecimal digits
optionally containing a radix character, then an optional
binary exponent part

o One of INF or INFINITY, or any other wide string equivalent
except for case

o 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
n-wchar-sequence nondigit

In default mode for wcstod(), only decimal, INF/INFINITY, and NAN/NAN(n-
wchar-sequence) forms are recognized. In C99/SUSv3 mode, hexadecimal
strings are also recognized.

In default mode for wcstod(), the n-wchar-sequence in the NAN(n-wchar-
sequence) form can contain any character except ')' (right parenthesis)
or '\0' (null). In C99/SUSv3 mode, the n-wchar-sequence can contain only
upper and lower case letters, digits, and '_' (underscore).

The wcstof() and wcstold() functions always function in
C99/SUSv3-conformant mode.

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) is interpreted as a floating
constant according to the rules of the C language, except that the radix
character is 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 is
assumed to follow the last digit in the string. If the subject sequence
begins with a minus sign, the sequence is interpreted as negated. A wide-
character sequence INF or INFINITY is interpreted as an infinity. A wide-
character sequence NAN or NAN(n-wchar-sequence(opt)) is interpreted as a
quiet NaN. A pointer to the final wide string is stored in the object
pointed to by endptr, provided that endptr is not a null pointer.

If the subject sequence has either the decimal or hexadecimal form, the
value resulting from the conversion is rounded correctly according to the
prevailing floating point rounding direction mode. The conversion also
raises floating point inexact, underflow, or overflow exceptions as

The radix character is 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 defaults to a period ('.').

If the subject sequence is empty or does not have the expected form, no
conversion is performed; the value of nptr is stored in the object
pointed to by endptr, provided that endptr is not a null pointer.

The wcstod() function does not change the setting of errno if successful.

The wstod() function is identical to wcstod().

The watof(str) function is equivalent to wstod(nptr, (wchar_t **)NULL).


Upon successful completion, these functions return the converted value.
If no conversion could be performed, 0 is returned.

If the correct value is outside the range of representable values,
+-HUGE_VAL, +-HUGE_VALF, or +-HUGE_VALL is returned (according to the
sign of the value), a floating point overflow exception is raised, and
errno is set to ERANGE. HUGE_VAL, HUGE_VALF, and HUGE_VALL are described
in math.h(3HEAD).

If the correct value would cause an underflow, the correctly rounded
result (which may be normal, subnormal, or zero) is returned, a floating
point underflow exception is raised, and errno is set to ERANGE.


The wcstod() and wstod() functions will fail if:

The value to be returned would cause overflow or underflow.

The wcstod() and wcstod() functions may fail if:

No conversion could be performed.


Because 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
call wcstod(), wcstof(), wcstold(), or wstod(), then check errno and if
it is non-zero, assume an error has occurred.


See attributes(7) for descriptions of the following attributes:

|Interface Stability | wcstod(), wcstof(), and |
| | wcstold() are Standard. |
|MT-Level | MT-Safe |


iswspace(3C), localeconv(3C), scanf(3C), setlocale(3C), wcstol(3C),
math.h(3HEAD), attributes(7), standards(7)

illumos April 21, 2021 WCSTOD(3C)