1WCSTOD(3P) POSIX Programmer's Manual WCSTOD(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 wcstod, wcstof, wcstold - convert a wide-character string to a double-
13 precision number
14
16 #include <wchar.h>
17 double wcstod(const wchar_t *restrict nptr, wchar_t **restrict endptr);
19 float wcstof(const wchar_t *restrict nptr, wchar_t **restrict endptr);
20 long double wcstold(const wchar_t *restrict nptr,
21 wchar_t **restrict endptr);
22
25 These functions shall convert the initial portion of the wide-character
26 string pointed to by nptr to double, float, and long double representa‐
27 tion, respectively. First, they shall decompose the input wide-charac‐
28 ter string into three parts:
29 1. An initial, possibly empty, sequence of white-space wide-character
31 codes (as specified by iswspace())
32 2. A subject sequence interpreted as a floating-point constant or rep‐
34 resenting infinity or NaN
35 3. A final wide-character string of one or more unrecognized wide-
37 character codes, including the terminating null wide-character code
38 of the input wide-character string
39 Then they shall attempt to convert the subject sequence to a floating-
41 point number, and return the result.
42 The expected form of the subject sequence is an optional plus or minus
44 sign, then one of the following:
45 * A non-empty sequence of decimal digits optionally containing a radix
47 character, then an optional exponent part
48 * A 0x or 0X, then a non-empty sequence of hexadecimal digits option‐
50 ally containing a radix character, then an optional binary exponent
51 part
52 * One of INF or INFINITY, or any other wide string equivalent except
54 for case
55 * One of NAN or NAN(n-wchar-sequence_opt), or any other wide string
57 ignoring case in the NAN part, where:
58 n-wchar-sequence:
61 digit
62 nondigit
63 n-wchar-sequence digit
64 n-wchar-sequence nondigit
65 The subject sequence is defined as the longest initial subsequence of
67 the input wide string, starting with the first non-white-space wide
68 character, that is of the expected form. The subject sequence contains
69 no wide characters if the input wide string is not of the expected
70 form.
71 If the subject sequence has the expected form for a floating-point num‐
73 ber, the sequence of wide characters starting with the first digit or
74 the radix character (whichever occurs first) shall be interpreted as a
75 floating constant according to the rules of the C language, except that
76 the radix character shall be used in place of a period, and that if
77 neither an exponent part nor a radix character appears in a decimal
78 floating-point number, or if a binary exponent part does not appear in
79 a hexadecimal floating-point number, an exponent part of the appropri‐
80 ate type with value zero shall be assumed to follow the last digit in
81 the string. If the subject sequence begins with a minus sign, the
82 sequence shall be interpreted as negated. A wide-character sequence INF
83 or INFINITY shall be interpreted as an infinity, if representable in
84 the return type, else as if it were a floating constant that is too
85 large for the range of the return type. A wide-character sequence NAN
86 or NAN(n-wchar-sequence_opt) shall be interpreted as a quiet NaN, if
87 supported in the return type, else as if it were a subject sequence
88 part that does not have the expected form; the meaning of the n-wchar
89 sequences is implementation-defined. A pointer to the final wide string
90 shall be stored in the object pointed to by endptr, provided that
91 endptr is not a null pointer.
92 If the subject sequence has the hexadecimal form and FLT_RADIX is a
94 power of 2, the conversion shall be rounded in an implementation-
95 defined manner.
96 The radix character shall be as defined in the program's locale (cate‐
98 gory LC_NUMERIC ). In the POSIX locale, or in a locale where the radix
99 character is not defined, the radix character shall default to a period
100 ( '.' ).
101 In other than the C or POSIX locales, other implementation-defined
103 subject sequences may be accepted.
104 If the subject sequence is empty or does not have the expected form, no
106 conversion shall be performed; the value of nptr shall be stored in the
107 object pointed to by endptr, provided that endptr is not a null
108 pointer.
109 The wcstod() function shall not change the setting of errno if success‐
111 ful.
112 Since 0 is returned on error and is also a valid return on success, an
114 application wishing to check for error situations should set errno to
115 0, then call wcstod(), wcstof(), or wcstold(), then check errno.
116
118 Upon successful completion, these functions shall return the converted
119 value. If no conversion could be performed, 0 shall be returned and
120 errno may be set to [EINVAL].
121 If the correct value is outside the range of representable values,
123 ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL shall be returned (according to
124 the sign of the value), and errno shall be set to [ERANGE].
125 If the correct value would cause underflow, a value whose magnitude is
127 no greater than the smallest normalized positive number in the return
128 type shall be returned and errno set to [ERANGE].
129
131 The wcstod() function shall fail if:
132 ERANGE The value to be returned would cause overflow or underflow.
134 The wcstod() function may fail if:
137 EINVAL No conversion could be performed.
139 The following sections are informative.
142
144 None.
145
147 If the subject sequence has the hexadecimal form and FLT_RADIX is not a
148 power of 2, and the result is not exactly representable, the result
149 should be one of the two numbers in the appropriate internal format
150 that are adjacent to the hexadecimal floating source value, with the
151 extra stipulation that the error should have a correct sign for the
152 current rounding direction.
153 If the subject sequence has the decimal form and at most DECIMAL_DIG
155 (defined in <float.h>) significant digits, the result should be cor‐
156 rectly rounded. If the subject sequence D has the decimal form and more
157 than DECIMAL_DIG significant digits, consider the two bounding, adja‐
158 cent decimal strings L and U, both having DECIMAL_DIG significant dig‐
159 its, such that the values of L, D, and U satisfy "L <= D <= U" . The
160 result should be one of the (equal or adjacent) values that would be
161 obtained by correctly rounding L and U according to the current round‐
162 ing direction, with the extra stipulation that the error with respect
163 to D should have a correct sign for the current rounding direction.
164
166 None.
167
169 None.
170
172 iswspace(), localeconv(), scanf(), setlocale(), wcstol(), the Base Def‐
173 initions volume of IEEE Std 1003.1-2001, Chapter 7, Locale, <float.h>,
174 <wchar.h>
175
177 Portions of this text are reprinted and reproduced in electronic form
178 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
179 -- Portable Operating System Interface (POSIX), The Open Group Base
180 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
181 Electrical and Electronics Engineers, Inc and The Open Group. In the
182 event of any discrepancy between this version and the original IEEE and
183 The Open Group Standard, the original IEEE and The Open Group Standard
184 is the referee document. The original Standard can be obtained online
185 at http://www.opengroup.org/unix/online.html .
186IEEE/The Open Group 2003 WCSTOD(3P)