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 <h3 class="section">2.7 <code>atof</code>, <code>atoff</code>&mdash;string to double or float</h3>

 <p><a name="index-atof-8"></a><a name="index-atoff-9"></a><strong>Synopsis</strong>
 <pre class="example">     #include &lt;stdlib.h&gt;
      double atof(const char *<var>s</var>);
      float atoff(const char *<var>s</var>);

 </pre>
    <p><strong>Description</strong><br>
 <code>atof</code> converts the initial portion of a string to a <code>double</code>.
 <code>atoff</code> converts the initial portion of a string to a <code>float</code>.

    <p>The functions parse the character string <var>s</var>,
 locating a substring which can be converted to a floating-point
 value. The substring must match the format:
 <pre class="smallexample">      [+|-]<var>digits</var>[.][<var>digits</var>][(e|E)[+|-]<var>digits</var>]
 </pre>
    <p>The substring converted is the longest initial
 fragment of <var>s</var> that has the expected format, beginning with
 the first non-whitespace character.  The substring
 is empty if <code>str</code> 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.

    <p><code>atof(</code><var>s</var><code>)</code> is implemented as <code>strtod(</code><var>s</var><code>, NULL)</code>.
 <code>atoff(</code><var>s</var><code>)</code> is implemented as <code>strtof(</code><var>s</var><code>, NULL)</code>.

    <p><br>
 <strong>Returns</strong><br>
 <code>atof</code> returns the converted substring value, if any, as a
 <code>double</code>; or <code>0.0</code>,  if no conversion could be performed.
 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
 <code>errno</code>.
 If the correct value would cause underflow, <code>0.0</code> is returned
 and <code>ERANGE</code> is stored in <code>errno</code>.

    <p><code>atoff</code> obeys the same rules as <code>atof</code>, except that it
 returns a <code>float</code>.

    <p><br>
 <strong>Portability</strong><br>
 <code>atof</code> is ANSI C. <code>atof</code>, <code>atoi</code>, and <code>atol</code> are subsumed by <code>strod</code>
 and <code>strol</code>, but are used extensively in existing code. These functions are
 less reliable, but may be faster if the argument is verified to be in a valid
 range.

    <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">2.7 <code>atof</code>, <code>atoff</code>—string to double or float</h3>

	<p><a name="index-atof-8"></a><a name="index-atoff-9"></a><strong>Synopsis</strong>
	<pre class="example"> #include <stdlib.h>
	double atof(const char *<var>s</var>);
	float atoff(const char *<var>s</var>);

	</pre>
	<p><strong>Description</strong><br>
	<code>atof</code> converts the initial portion of a string to a <code>double</code>.
	<code>atoff</code> converts the initial portion of a string to a <code>float</code>.

	<p>The functions parse the character string <var>s</var>,
	locating a substring which can be converted to a floating-point
	value. The substring must match the format:
	<pre class="smallexample"> [+\|-]<var>digits</var>[.][<var>digits</var>][(e\|E)[+\|-]<var>digits</var>]
	</pre>
	<p>The substring converted is the longest initial
	fragment of <var>s</var> that has the expected format, beginning with
	the first non-whitespace character. The substring
	is empty if <code>str</code> 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.

	<p><code>atof(</code><var>s</var><code>)</code> is implemented as <code>strtod(</code><var>s</var><code>, NULL)</code>.
	<code>atoff(</code><var>s</var><code>)</code> is implemented as <code>strtof(</code><var>s</var><code>, NULL)</code>.

	<p><br>
	<strong>Returns</strong><br>
	<code>atof</code> returns the converted substring value, if any, as a
	<code>double</code>; or <code>0.0</code>, if no conversion could be performed.
	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
	<code>errno</code>.
	If the correct value would cause underflow, <code>0.0</code> is returned
	and <code>ERANGE</code> is stored in <code>errno</code>.

	<p><code>atoff</code> obeys the same rules as <code>atof</code>, except that it
	returns a <code>float</code>.

	<p><br>
	<strong>Portability</strong><br>
	<code>atof</code> is ANSI C. <code>atof</code>, <code>atoi</code>, and <code>atol</code> are subsumed by <code>strod</code>
	and <code>strol</code>, but are used extensively in existing code. These functions are
	less reliable, but may be faster if the argument is verified to be in a valid
	range.

	<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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