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123 lines
5.4 KiB
HTML
123 lines
5.4 KiB
HTML
4 years ago
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<title>atof (The Red Hat newlib C Library)</title>
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<link href="Document-Index.html#Document-Index" rel="index" title="Document Index">
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<link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Stdlib.html#Stdlib" rel="up" title="Stdlib">
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<link href="atoi.html#atoi" rel="next" title="atoi">
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</head>
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<body lang="en">
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<a name="atof"></a>
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<div class="header">
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<p>
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Next: <a href="atoi.html#atoi" accesskey="n" rel="next">atoi</a>, Previous: <a href="atexit.html#atexit" accesskey="p" rel="prev">atexit</a>, Up: <a href="Stdlib.html#Stdlib" accesskey="u" rel="up">Stdlib</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="atof_002c-atoff_002d_002d_002dstring-to-double-or-float"></a>
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<h3 class="section">2.7 <code>atof</code>, <code>atoff</code>—string to double or float</h3>
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<a name="index-atof"></a>
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<a name="index-atoff"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">#include <stdlib.h>
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double atof(const char *<var>s</var>);
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float atoff(const char *<var>s</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>atof</code> converts the initial portion of a string to a <code>double</code>.
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<code>atoff</code> converts the initial portion of a string to a <code>float</code>.
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</p>
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<p>The functions parse the character string <var>s</var>,
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locating a substring which can be converted to a floating-point
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value. The substring must match the format:
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</p><div class="smallexample">
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<pre class="smallexample"> [+|-]<var>digits</var>[.][<var>digits</var>][(e|E)[+|-]<var>digits</var>]
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</pre></div>
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<p>The substring converted is the longest initial
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fragment of <var>s</var> that has the expected format, beginning with
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the first non-whitespace character. The substring
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is empty if <code>str</code> is empty, consists entirely
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of whitespace, or if the first non-whitespace character is
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something other than <code>+</code>, <code>-</code>, <code>.</code>, or a digit.
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</p>
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<p><code>atof(<var>s</var>)</code> is implemented as <code>strtod(<var>s</var>, NULL)</code>.
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<code>atoff(<var>s</var>)</code> is implemented as <code>strtof(<var>s</var>, NULL)</code>.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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<code>atof</code> returns the converted substring value, if any, as a
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<code>double</code>; or <code>0.0</code>, if no conversion could be performed.
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If the correct value is out of the range of representable values, plus
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or minus <code>HUGE_VAL</code> is returned, and <code>ERANGE</code> is stored in
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<code>errno</code>.
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If the correct value would cause underflow, <code>0.0</code> is returned
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and <code>ERANGE</code> is stored in <code>errno</code>.
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</p>
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<p><code>atoff</code> obeys the same rules as <code>atof</code>, except that it
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returns a <code>float</code>.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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<code>atof</code> is ANSI C. <code>atof</code>, <code>atoi</code>, and <code>atol</code> are subsumed by <code>strod</code>
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and <code>strol</code>, but are used extensively in existing code. These functions are
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less reliable, but may be faster if the argument is verified to be in a valid
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range.
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</p>
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<p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>,
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<code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>.
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</p>
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<br>
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<hr>
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<div class="header">
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<p>
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Next: <a href="atoi.html#atoi" accesskey="n" rel="next">atoi</a>, Previous: <a href="atexit.html#atexit" accesskey="p" rel="prev">atexit</a>, Up: <a href="Stdlib.html#Stdlib" accesskey="u" rel="up">Stdlib</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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