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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>
<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>&mdash;string to double or float</h3>
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<a name="index-strtold"></a>
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<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;stdlib.h&gt;
double strtod(const char *restrict <var>str</var>, char **restrict <var>tail</var>);
float strtof(const char *restrict <var>str</var>, char **restrict <var>tail</var>);
long double strtold(const char *restrict <var>str</var>,
    char **restrict <var>tail</var>);

#include &lt;stdlib.h&gt;
double strtod_l(const char *restrict <var>str</var>, char **restrict <var>tail</var>,
    locale_t <var>locale</var>);
float strtof_l(const char *restrict <var>str</var>, char **restrict <var>tail</var>,
    locale_t <var>locale</var>);
long double strtold_l(const char *restrict <var>str</var>,
    char **restrict <var>tail</var>,
    locale_t <var>locale</var>);

double _strtod_r(void *<var>reent</var>,
    const char *restrict <var>str</var>, char **restrict <var>tail</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>strtod</code>, <code>strtof</code>, <code>strtold</code> parse the character string
<var>str</var>, producing a substring which can be converted to a double,
float, or long double value, respectively.  The substring converted
is the longest initial subsequence of <var>str</var>, beginning with the
first non-whitespace character, that has one of these formats:
</p><div class="smallexample">
<pre class="smallexample">[+|-]<var>digits</var>[.[<var>digits</var>]][(e|E)[+|-]<var>digits</var>]
[+|-].<var>digits</var>[(e|E)[+|-]<var>digits</var>]
[+|-](i|I)(n|N)(f|F)[(i|I)(n|N)(i|I)(t|T)(y|Y)]
[+|-](n|N)(a|A)(n|N)[&lt;(&gt;[<var>hexdigits</var>]&lt;)&gt;]
[+|-]0(x|X)<var>hexdigits</var>[.[<var>hexdigits</var>]][(p|P)[+|-]<var>digits</var>]
[+|-]0(x|X).<var>hexdigits</var>[(p|P)[+|-]<var>digits</var>]
</pre></div>
<p>The substring contains no characters if <var>str</var> is empty, consists
entirely of whitespace, or if the first non-whitespace
character is something other than <code>+</code>, <code>-</code>, <code>.</code>, or a
digit, and cannot be parsed as infinity or NaN. If the platform
does not support NaN, then NaN is treated as an empty substring.
If the substring is empty, no conversion is done, and
the value of <var>str</var> is stored in <code>*<var>tail</var></code>.  Otherwise,
the substring is converted, and a pointer to the final string
(which will contain at least the terminating null character of
<var>str</var>) is stored in <code>*<var>tail</var></code>.  If you want no
assignment to <code>*<var>tail</var></code>, pass a null pointer as <var>tail</var>.
</p>
<p>This implementation returns the nearest machine number to the
input decimal string.  Ties are broken by using the IEEE
round-even rule.  However, <code>strtof</code> is currently subject to
double rounding errors.
</p>
<p><code>strtod_l</code>, <code>strtof_l</code>, <code>strtold_l</code> are like <code>strtod</code>,
<code>strtof</code>, <code>strtold</code> but perform the conversion based on the
locale specified by the locale object locale.  If <var>locale</var> is
LC_GLOBAL_LOCALE or not a valid locale object, the behaviour is
undefined.
</p>
<p>The alternate function <code>_strtod_r</code> is a reentrant version.
The extra argument <var>reent</var> is a pointer to a reentrancy structure.
</p>
<br>
<p><strong>Returns</strong><br>
These functions return the converted substring value, if any.  If
no conversion could be performed, 0 is returned.  If the correct
value is out of the range of representable values, plus or minus
<code>HUGE_VAL</code> (<code>HUGE_VALF</code>, <code>HUGE_VALL</code>) is returned, and
<code>ERANGE</code> is stored in errno. If the correct value would cause
underflow, 0 is returned and <code>ERANGE</code> is stored in errno.
</p>
<br>
<p><strong>Portability</strong><br>
<code>strtod</code> is ANSI.
<code>strtof</code>, <code>strtold</code> are C99.
<code>strtod_l</code>, <code>strtof_l</code>, <code>strtold_l</code> are GNU extensions.
</p>
<p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>,
<code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>.
</p>
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