strtod.html
来自「unix 下的C开发手册,还用详细的例程。」· HTML 代码 · 共 167 行
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>strtod</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_009_213"> </a>NAME</h4><blockquote>strtod - convert string to a double-precision number</blockquote><h4><a name = "tag_000_009_214"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="stdlib.h.html">stdlib.h</a>>double strtod(const char *<i>str</i>, char **<i>endptr</i>);</code></pre></blockquote><h4><a name = "tag_000_009_215"> </a>DESCRIPTION</h4><blockquote>The<i>strtod()</i>function converts the initial portion of the string pointed to by<i>str</i>to type<b>double</b>representation.First it decomposes the input string into three parts: aninitial, possibly empty, sequence of white-space characters (asspecified by<i><a href="isspace.html">isspace()</a></i>);a subject sequence interpreted as a floating-pointconstant; and a final string of one or more unrecognisedcharacters, including the terminating null byte of the inputstring.Then it attempts to convert the subject sequence to afloating-point number, and returns the result.<p>The expected form of the subject sequence is an optional + or- sign, then a non-empty sequence of digits optionally containing aradix character, then an optional exponent part.An exponent part consists of e or E,followed by an optional sign, followed by one or more decimal digits.The subject sequence is defined as the longest initial subsequence ofthe input string, starting with the first non-white-space character,that is of the expected form.The subject sequence is empty if the input stringis empty or consists entirely of white-space characters, or if the firstcharacter that is not white space is other than a sign, a digit or aradix character.<p>If the subject sequence has the expected form, the sequencestarting with the first digit or the radix character(whichever occurs first) is interpreted as afloating constant of the C language,except that the radix character is used inplace of a period, and that if neither an exponent part nor aradix character appears, a radix character is assumed tofollow the last digit in the string.If the subject sequence begins with a minus sign, the valueresulting from the conversion is negated.A pointer to the final string is stored in the object pointed toby<i>endptr</i>,provided that<i>endptr</i>is not a null pointer.<p>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 isnot defined, the radix character defaults to a period (.).<p>In other than the POSIX locale, other implementation-dependentsubject sequence forms may be accepted.<p>If the subject sequence is empty or does not have the expectedform, no conversion is performed; the value of<i>str</i>is stored in the object pointed to by<i>endptr</i>,provided that<i>endptr</i>is not a null pointer.<br><p>The<i>strtod()</i>function will not change the setting of <b>errno</b>if successful.<p>Because 0 is returned on error and is also a valid return on success, anapplication wishing to check for error situations should set<i>errno</i>to 0, then call<i>strtod()</i>,then check<i>errno</i>.</blockquote><h4><a name = "tag_000_009_216"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>strtod()</i>returns the converted value.If no conversion could be performed, 0 is returned, and<i>errno</i>may be set to [EINVAL].<p>If the correct value is outside the range of representablevalues, ±HUGE_VALis returned (according to the sign of the value), and<i>errno</i>is set to [ERANGE].<p>If the correct value would cause an underflow, 0 is returned and<i>errno</i>is set to [ERANGE].<br></blockquote><h4><a name = "tag_000_009_217"> </a>ERRORS</h4><blockquote>The<i>strtod()</i>function will fail if:<dl compact><dt>[ERANGE]<dd>The value to be returned would cause overflow or underflow.</dl><p>The<i>strtod()</i>function may fail if:<dl compact><dt>[EINVAL]<dd>No conversion could be performed.</dl></blockquote><h4><a name = "tag_000_009_218"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_009_219"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_009_220"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_009_221"> </a>SEE ALSO</h4><blockquote><i><a href="isspace.html">isspace()</a></i>,<i><a href="localeconv.html">localeconv()</a></i>,<i><a href="scanf.html">scanf()</a></i>,<i><a href="setlocale.html">setlocale()</a></i>,<i><a href="strtol.html">strtol()</a></i>,<i><a href="stdlib.h.html"><stdlib.h></a></i>,the <b>XBD</b> specification, <a href="../xbd/locale.html"><b>Locale</b> </a>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 1 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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