WCSTOD(3C)WCSTOD(3C)NAME
wcstod, wcstof, wcstold, wstod, watof - convert wide character string
to floating-point 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);
double wstod(const wchar_t *nptr, wchar_t **endptr);
double watof(wchar_t *nptr);
DESCRIPTION
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 decom‐
pose 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
nondigit
n-wchar-sequence digit
n-wchar-sequence nondigit
In default mode for wcstod(), only decimal, INF/INFINITY, and
NAN/NAN(n-char-sequence) forms are recognized. In C99/SUSv3 mode, hexa‐
decimal strings are also recognized.
In default mode for wcstod(), the n-char-sequence in the NAN(n-char-
equence) form can contain any character except ')' (right parenthesis)
or '\0' (null). In C99/SUSv3 mode, the n-char-sequence can contain
only upper and lower case letters, digits, and '_' (underscore).
The wcstof() and wcstold() functions always function in C99/SUSv3-con‐
formant 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 num‐
ber, the sequence of wide characters starting with the first digit or
the radix character (whichever occurs first) is interpreted as a float‐
ing 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 appropriate.
The radix character is defined in the program's locale (category
LC_NUMERIC). In the POSIX locale, or in a locale where the radix char‐
acter 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 success‐
ful.
The wstod() function is identical to wcstod().
The watof(str) function is equivalent to wstod(nptr, (wchar_t **)NULL).
RETURN VALUES
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.
If the correct value would cause an underflow, the correctly rounded
result (which may be normal, subnormal, or zero) is returned, a float‐
ing point underflow exception is raised, and errno is set to ERANGE.
ERRORS
The wcstod() and wstod() functions will fail if:
ERANGE
The value to be returned would cause overflow or underflow.
The wcstod() and wcstod() functions may fail if:
EINVAL
No conversion could be performed.
USAGE
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.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬────────────────────────────┐
│ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼────────────────────────────┤
│Interface Stability │ wcstod(), wcstof(), and │
│ │ wcstold() are Standard. │
├────────────────────┼────────────────────────────┤
│MT-Level │ MT-Safe │
└────────────────────┴────────────────────────────┘
SEE ALSOiswspace(3C), localeconv(3C), scanf(3C), setlocale(3C), wcstol(3C),
attributes(5), standards(5)
Mar 31, 2003 WCSTOD(3C)
