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 <h3 class="section">2.34 <code>strtod</code>, <code>strtof</code>&mdash;string to double or float</h3>

 <p><a name="index-strtod-79"></a><a name="index-g_t_005fstrtod_005fr-80"></a><a name="index-strtof-81"></a><strong>Synopsis</strong>
 <pre class="example">     #include &lt;stdlib.h&gt;
      double strtod(const char *<var>str</var>, char **<var>tail</var>);
      float strtof(const char *<var>str</var>, char **<var>tail</var>);

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

 </pre>
    <p><strong>Description</strong><br>
 The function <code>strtod</code> parses the character string <var>str</var>,
 producing a substring which can be converted to a double
 value.  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:
 <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>
    <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>*</code><var>tail</var>.  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>*</code><var>tail</var>.  If you want no
 assignment to <code>*</code><var>tail</var>, pass a null pointer as <var>tail</var>.
 <code>strtof</code> is identical to <code>strtod</code> except for its return type.

    <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>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>
 <strong>Returns</strong><br>
 <code>strtod</code> returns 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> 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>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><br>

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	<h3 class="section">2.34 <code>strtod</code>, <code>strtof</code>—string to double or float</h3>

	<p><a name="index-strtod-79"></a><a name="index-g_t_005fstrtod_005fr-80"></a><a name="index-strtof-81"></a><strong>Synopsis</strong>
	<pre class="example"> #include <stdlib.h>
	double strtod(const char <var>str</var>, char *<var>tail</var>);
	float strtof(const char <var>str</var>, char *<var>tail</var>);

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

	</pre>
	<p><strong>Description</strong><br>
	The function <code>strtod</code> parses the character string <var>str</var>,
	producing a substring which can be converted to a double
	value. 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:
	<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)[<(>[<var>hexdigits</var>]<)>]
	[+\|-]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>
	<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>*</code><var>tail</var>. 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>*</code><var>tail</var>. If you want no
	assignment to <code>*</code><var>tail</var>, pass a null pointer as <var>tail</var>.
	<code>strtof</code> is identical to <code>strtod</code> except for its return type.

	<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>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>
	<strong>Returns</strong><br>
	<code>strtod</code> returns 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> 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>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><br>

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