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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>nextafter</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="nextafter"></a> <a name="tag_03_404"></a><!-- nextafter --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_404_01"></a>NAME</h4><blockquote>nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl - next representable floating-pointnumber</blockquote><h4><a name="tag_03_404_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/math.h.html">math.h</a>><br><br> double nextafter(double</tt> <i>x</i><tt>, double</tt> <i>y</i><tt>);<br> float nextafterf(float</tt> <i>x</i><tt>, float</tt> <i>y</i><tt>);<br> long double nextafterl(long double</tt> <i>x</i><tt>, long double</tt> <i>y</i><tt>);<br> double nexttoward(double</tt> <i>x</i><tt>, long double</tt> <i>y</i><tt>);<br> float nexttowardf(float</tt> <i>x</i><tt>, long double</tt> <i>y</i><tt>);<br> long double nexttowardl(long double</tt> <i>x</i><tt>, long double</tt> <i>y</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_404_03"></a>DESCRIPTION</h4><blockquote><div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between therequirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers tothe ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div><p>The <i>nextafter</i>(), <i>nextafterf</i>(), and <i>nextafterl</i>() functions shall compute the next representablefloating-point value following <i>x</i> in the direction of <i>y</i>. Thus, if <i>y</i> is less than <i>x</i>, <i>nextafter</i>()shall return the largest representable floating-point number less than <i>x</i>. The <i>nextafter</i>(), <i>nextafterf</i>(), and<i>nextafterl</i>() functions shall return <i>y</i> if <i>x</i> equals <i>y</i>.</p><p>The <i>nexttoward</i>(), <i>nexttowardf</i>(), and <i>nexttowardl</i>() functions shall be equivalent to the corresponding<i>nextafter</i>() functions, except that the second parameter shall have type <b>long double</b> and the functions shall return<i>y</i> converted to the type of the function if <i>x</i> equals <i>y</i>.</p><p>An application wishing to check for error situations should set <i>errno</i> to zero and call<i>feclearexcept</i>(FE_ALL_EXCEPT) before calling these functions. On return, if <i>errno</i> is non-zero or<i>fetestexcept</i>(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.</p></blockquote><h4><a name="tag_03_404_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, these functions shall return the next representable floating-point value following <i>x</i> in thedirection of <i>y</i>.</p><p>If <i>x</i>== <i>y</i>, <i>y</i> (of the type <i>x</i>) shall be returned.</p><p>If <i>x</i> is finite and the correct function value would overflow, a range error shall occur and ±HUGE_VAL,±HUGE_VALF, and ±HUGE_VALL (with the same sign as <i>x</i>) shall be returned as appropriate for the return type ofthe function.</p><p><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> If<i>x</i> or <i>y</i> is NaN, a NaN shall be returned.</p><p>If <i>x</i>!= <i>y</i> and the correct function value is subnormal, zero, or underflows, a range error shall occur, and eitherthe correct function value (if representable) or 0.0 shall be returned. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_03_404_05"></a>ERRORS</h4><blockquote><p>These functions shall fail if:</p><dl compact><dt>Range Error</dt><dd>The correct value overflows. <p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [ERANGE]. If theinteger expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall beraised.</p></dd><dt>Range Error</dt><dd><sup>[<a href="javascript:open_code('MX')">MX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The correct value is subnormal or underflows. <p>If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then <i>errno</i> shall be set to [ERANGE]. If theinteger expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall beraised. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_404_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_404_07"></a>APPLICATION USAGE</h4><blockquote><p>On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent ofeach other, but at least one of them must be non-zero.</p></blockquote><h4><a name="tag_03_404_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_404_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_404_10"></a>SEE ALSO</h4><blockquote><p><a href="feclearexcept.html"><i>feclearexcept</i>()</a>, <a href="fetestexcept.html"><i>fetestexcept</i>()</a>, the BaseDefinitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap04.html#tag_04_18">Section 4.18, Treatment ofError Conditions for Mathematical Functions</a>, <a href="../basedefs/math.h.html"><i><math.h></i></a></p></blockquote><h4><a name="tag_03_404_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4, Version 2.</p></blockquote><h4><a name="tag_03_404_12"></a>Issue 5</h4><blockquote><p>Moved from X/OPEN UNIX extension to BASE.</p></blockquote><h4><a name="tag_03_404_13"></a>Issue 6</h4><blockquote><p>The <i>nextafter</i>() function is no longer marked as an extension.</p><p>The <i>nextafterf</i>(), <i>nextafterl</i>(), <i>nexttoward</i>(), <i>nexttowardf</i>(), and <i>nexttowardl</i>() functions areadded for alignment with the ISO/IEC 9899:1999 standard.</p><p>The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999standard.</p><p>IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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