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285 lines
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<title>wcstod</title>
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<basefont size="3"> <a name="wcstod"></a> <a name="tag_03_842"></a><!-- wcstod -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_842_01"></a>NAME</h4>
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<blockquote>wcstod, wcstof, wcstold - convert a wide-character string to a double-precision number</blockquote>
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<h4><a name="tag_03_842_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<p><code><tt>#include <<a href="../basedefs/wchar.h.html">wchar.h</a>><br>
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<br>
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double wcstod(const wchar_t *restrict</tt> <i>nptr</i><tt>, wchar_t **restrict</tt> <i>endptr</i><tt>);<br>
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float wcstof(const wchar_t *restrict</tt> <i>nptr</i><tt>, wchar_t **restrict</tt> <i>endptr</i><tt>);<br>
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long double wcstold(const wchar_t *restrict</tt> <i>nptr</i><tt>,<br>
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wchar_t **restrict</tt> <i>endptr</i><tt>);<br>
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</tt></code></p>
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</blockquote>
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<h4><a name="tag_03_842_03"></a>DESCRIPTION</h4>
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<blockquote>
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<div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"
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border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the
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requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to
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the ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div>
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<p>These functions shall convert the initial portion of the wide-character string pointed to by <i>nptr</i> to <b>double</b>,
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<b>float</b>, and <b>long double</b> representation, respectively. First, they shall decompose the input wide-character string into
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three parts:</p>
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<ol>
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<li>
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<p>An initial, possibly empty, sequence of white-space wide-character codes (as specified by <a href=
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"../functions/iswspace.html"><i>iswspace</i>()</a>)</p>
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</li>
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<li>
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<p>A subject sequence interpreted as a floating-point constant or representing infinity or NaN</p>
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</li>
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<li>
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<p>A final wide-character string of one or more unrecognized wide-character codes, including the terminating null wide-character
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code of the input wide-character string</p>
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</li>
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</ol>
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<p>Then they shall attempt to convert the subject sequence to a floating-point number, and return the result.</p>
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<p>The expected form of the subject sequence is an optional plus or minus sign, then one of the following:</p>
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<ul>
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<li>
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<p>A non-empty sequence of decimal digits optionally containing a radix character, then an optional exponent part</p>
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</li>
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<li>
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<p>A 0x or 0X, then a non-empty sequence of hexadecimal digits optionally containing a radix character, then an optional binary
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exponent part</p>
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</li>
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<li>
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<p>One of INF or INFINITY, or any other wide string equivalent except for case</p>
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</li>
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<li>
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<p>One of NAN or NAN(<i>n-wchar-sequence<small><sub>opt</sub></small></i>), or any other wide string ignoring case in the NAN part,
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where:</p>
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<pre>
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<tt>n-wchar-sequence:
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digit
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nondigit
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n-wchar-sequence digit
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n-wchar-sequence nondigit
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</tt>
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</pre>
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</li>
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</ul>
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<p>The subject sequence is defined as the longest initial subsequence of the input wide string, starting with the first
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non-white-space wide character, that is of the expected form. The subject sequence contains no wide characters if the input wide
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string is not of the expected form.</p>
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<p>If the subject sequence has the expected form for a floating-point number, the sequence of wide characters starting with the
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first digit or the radix character (whichever occurs first) shall be interpreted as a floating constant according to the rules of
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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
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radix character appears in a decimal floating-point number, or if a binary exponent part does not appear in a hexadecimal
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floating-point number, an exponent part of the appropriate type with value zero shall be assumed to follow the last digit in the
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string. If the subject sequence begins with a minus sign, the sequence shall be interpreted as negated. A wide-character sequence
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INF or INFINITY shall be interpreted as an infinity, if representable in the return type, else as if it were a floating constant
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that is too large for the range of the return type. A wide-character sequence NAN or
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NAN(<i>n-wchar-sequence<small><sub>opt</sub></small></i>) shall be interpreted as a quiet NaN, if supported in the return type,
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else as if it were a subject sequence part that does not have the expected form; the meaning of the <i>n</i>-wchar sequences is
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implementation-defined. A pointer to the final wide string shall be stored in the object pointed to by <i>endptr</i>, provided that
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<i>endptr</i> is not a null pointer.</p>
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<p>If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the conversion shall be rounded in an
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implementation-defined manner.</p>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The
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radix character shall be as defined in the program's locale (category <i>LC_NUMERIC ).</i> In the POSIX locale, or in a locale
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where the radix character is not defined, the radix character shall default to a period ( <tt>'.'</tt> ). <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p>In other than the C <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> or POSIX <img src="../images/opt-end.gif" alt="[Option End]" border="0"> locales, other
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implementation-defined subject sequences may be accepted.</p>
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<p>If the subject sequence is empty or does not have the expected form, no conversion shall be performed; the value of <i>nptr</i>
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shall be stored in the object pointed to by <i>endptr</i>, provided that <i>endptr</i> is not a null pointer.</p>
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<p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The
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<i>wcstod</i>() function shall not change the setting of <i>errno</i> if successful.</p>
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<p>Since 0 is returned on error and is also a valid return on success, an application wishing to check for error situations should
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set <i>errno</i> to 0, then call <i>wcstod</i>(), <i>wcstof</i>(), or <i>wcstold</i>(), then check <i>errno</i>. <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></p>
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</blockquote>
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<h4><a name="tag_03_842_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, these functions shall return the converted value. If no conversion could be performed, 0 shall be
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returned <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border=
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"0"> and <i>errno</i> may be set to [EINVAL]. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p>If the correct value is outside the range of representable values, plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL shall be
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returned (according to the sign of the value), and <i>errno</i> shall be set to [ERANGE].</p>
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<p>If the correct value would cause underflow, a value whose magnitude is no greater than the smallest normalized positive number
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in the return type shall be returned and <i>errno</i> set to [ERANGE].</p>
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</blockquote>
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<h4><a name="tag_03_842_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>wcstod</i>() function shall fail if:</p>
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<dl compact>
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<dt>[ERANGE]</dt>
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<dd>The value to be returned would cause overflow or underflow.</dd>
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</dl>
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<p>The <i>wcstod</i>() function may fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> No
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conversion could be performed. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_842_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_842_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>If the subject sequence has the hexadecimal form and FLT_RADIX is not a power of 2, and the result is not exactly representable,
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the result should be one of the two numbers in the appropriate internal format that are adjacent to the hexadecimal floating source
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value, with the extra stipulation that the error should have a correct sign for the current rounding direction.</p>
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<p>If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in <a href=
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"../basedefs/float.h.html"><i><float.h></i></a>) significant digits, the result should be correctly rounded. If the subject
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sequence <i>D</i> has the decimal form and more than DECIMAL_DIG significant digits, consider the two bounding, adjacent decimal
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strings <i>L</i> and <i>U</i>, both having DECIMAL_DIG significant digits, such that the values of <i>L</i>, <i>D</i>, and <i>U</i>
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satisfy <tt>"L <= D <= U"</tt> . The result should be one of the (equal or adjacent) values that would be obtained by
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correctly rounding <i>L</i> and <i>U</i> according to the current rounding direction, with the extra stipulation that the error
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with respect to <i>D</i> should have a correct sign for the current rounding direction.</p>
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</blockquote>
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<h4><a name="tag_03_842_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_842_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_842_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="iswspace.html"><i>iswspace</i>()</a> , <a href="localeconv.html"><i>localeconv</i>()</a> , <a href=
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"scanf.html"><i>scanf</i>()</a> , <a href="setlocale.html"><i>setlocale</i>()</a> , <a href="wcstol.html"><i>wcstol</i>()</a> , the
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Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap07.html">Chapter 7, Locale</a>, <a href=
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"../basedefs/float.h.html"><i><float.h></i></a>, <a href="../basedefs/wchar.h.html"><i><wchar.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_842_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 4. Derived from the MSE working draft.</p>
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</blockquote>
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<h4><a name="tag_03_842_12"></a>Issue 5</h4>
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<blockquote>
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<p>The DESCRIPTION is updated to indicate that <i>errno</i> is not changed if the function is successful.</p>
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</blockquote>
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<h4><a name="tag_03_842_13"></a>Issue 6</h4>
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<blockquote>
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<p>Extensions beyond the ISO C standard are marked.</p>
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<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>
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<ul>
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<li>
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<p>In the RETURN VALUE and ERRORS sections, the [EINVAL] optional error condition is added if no conversion could be performed.</p>
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</li>
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</ul>
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<p>The following changes are made for alignment with the ISO/IEC 9899:1999 standard:</p>
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<ul>
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<li>
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<p>The <i>wcstod</i>() prototype is updated.</p>
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</li>
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<li>
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<p>The <i>wcstof</i>() and <i>wcstold</i>() functions are added.</p>
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</li>
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<li>
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<p>If the correct value for <i>wcstod</i>() would cause underflow, the return value changed from 0 (as specified in Issue 5) to the
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smallest normalized positive number.</p>
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</li>
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<li>
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<p>The DESCRIPTION, RETURN VALUE, and APPLICATION USAGE sections are extensively updated.</p>
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</li>
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</ul>
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<p>ISO/IEC 9899:1999 standard, Technical Corrigendum No. 1 is incorporated.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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