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157 lines
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157 lines
7.5 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>strtod (The Red Hat newlib C Library)</title>
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<meta name="description" content="strtod (The Red Hat newlib C Library)">
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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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<body lang="en">
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<a name="strtod"></a>
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<div class="header">
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<p>
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Next: <a href="strtol.html#strtol" accesskey="n" rel="next">strtol</a>, Previous: <a href="rpmatch.html#rpmatch" accesskey="p" rel="prev">rpmatch</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="strtod_002c-strtof_002c-strtold_002c-strtod_005fl_002c-strtof_005fl_002c-strtold_005fl_002d_002d_002dstring-to-double-or-float"></a>
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<h3 class="section">2.37 <code>strtod</code>, <code>strtof</code>, <code>strtold</code>, <code>strtod_l</code>, <code>strtof_l</code>, <code>strtold_l</code>—string to double or float</h3>
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<a name="index-strtod"></a>
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<a name="index-strtof"></a>
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<a name="index-strtold"></a>
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<a name="index-strtod_005fl"></a>
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<a name="index-strtof_005fl"></a>
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<a name="index-strtold_005fl"></a>
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<a name="index-_005fstrtod_005fr"></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 strtod(const char *restrict <var>str</var>, char **restrict <var>tail</var>);
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float strtof(const char *restrict <var>str</var>, char **restrict <var>tail</var>);
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long double strtold(const char *restrict <var>str</var>,
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char **restrict <var>tail</var>);
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#include <stdlib.h>
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double strtod_l(const char *restrict <var>str</var>, char **restrict <var>tail</var>,
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locale_t <var>locale</var>);
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float strtof_l(const char *restrict <var>str</var>, char **restrict <var>tail</var>,
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locale_t <var>locale</var>);
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long double strtold_l(const char *restrict <var>str</var>,
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char **restrict <var>tail</var>,
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locale_t <var>locale</var>);
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double _strtod_r(void *<var>reent</var>,
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const char *restrict <var>str</var>, char **restrict <var>tail</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>strtod</code>, <code>strtof</code>, <code>strtold</code> parse the character string
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<var>str</var>, producing a substring which can be converted to a double,
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float, or long double value, respectively. The substring converted
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is the longest initial subsequence of <var>str</var>, beginning with the
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first non-whitespace character, that has one of these formats:
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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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[+|-].<var>digits</var>[(e|E)[+|-]<var>digits</var>]
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[+|-](i|I)(n|N)(f|F)[(i|I)(n|N)(i|I)(t|T)(y|Y)]
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[+|-](n|N)(a|A)(n|N)[<(>[<var>hexdigits</var>]<)>]
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[+|-]0(x|X)<var>hexdigits</var>[.[<var>hexdigits</var>]][(p|P)[+|-]<var>digits</var>]
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[+|-]0(x|X).<var>hexdigits</var>[(p|P)[+|-]<var>digits</var>]
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</pre></div>
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<p>The substring contains no characters if <var>str</var> is empty, consists
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entirely of whitespace, or if the first non-whitespace
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character is something other than <code>+</code>, <code>-</code>, <code>.</code>, or a
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digit, and cannot be parsed as infinity or NaN. If the platform
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does not support NaN, then NaN is treated as an empty substring.
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If the substring is empty, no conversion is done, and
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the value of <var>str</var> is stored in <code>*<var>tail</var></code>. Otherwise,
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the substring is converted, and a pointer to the final string
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(which will contain at least the terminating null character of
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<var>str</var>) is stored in <code>*<var>tail</var></code>. If you want no
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assignment to <code>*<var>tail</var></code>, pass a null pointer as <var>tail</var>.
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</p>
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<p>This implementation returns the nearest machine number to the
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input decimal string. Ties are broken by using the IEEE
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round-even rule. However, <code>strtof</code> is currently subject to
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double rounding errors.
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</p>
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<p><code>strtod_l</code>, <code>strtof_l</code>, <code>strtold_l</code> are like <code>strtod</code>,
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<code>strtof</code>, <code>strtold</code> but perform the conversion based on the
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locale specified by the locale object locale. If <var>locale</var> is
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LC_GLOBAL_LOCALE or not a valid locale object, the behaviour is
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undefined.
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</p>
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<p>The alternate function <code>_strtod_r</code> is a reentrant version.
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The extra argument <var>reent</var> is a pointer to a reentrancy structure.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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These functions return the converted substring value, if any. If
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no conversion could be performed, 0 is returned. If the correct
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value is out of the range of representable values, plus or minus
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<code>HUGE_VAL</code> (<code>HUGE_VALF</code>, <code>HUGE_VALL</code>) is returned, and
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<code>ERANGE</code> is stored in errno. If the correct value would cause
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underflow, 0 is returned and <code>ERANGE</code> is stored in errno.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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<code>strtod</code> is ANSI.
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<code>strtof</code>, <code>strtold</code> are C99.
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<code>strtod_l</code>, <code>strtof_l</code>, <code>strtold_l</code> are GNU extensions.
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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="strtol.html#strtol" accesskey="n" rel="next">strtol</a>, Previous: <a href="rpmatch.html#rpmatch" accesskey="p" rel="prev">rpmatch</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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