<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ --> <head> <title>atof (The Red Hat newlib C Library)</title> <meta name="description" content="atof (The Red Hat newlib C Library)"> <meta name="keywords" content="atof (The Red Hat newlib C Library)"> <meta name="resource-type" content="document"> <meta name="distribution" content="global"> <meta name="Generator" content="makeinfo"> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <link href="index.html#Top" rel="start" title="Top"> <link href="Document-Index.html#Document-Index" rel="index" title="Document Index"> <link href="Document-Index.html#SEC_Contents" rel="contents" title="Table of Contents"> <link href="Stdlib.html#Stdlib" rel="up" title="Stdlib"> <link href="atoi.html#atoi" rel="next" title="atoi"> <link href="atexit.html#atexit" rel="prev" title="atexit"> <style type="text/css"> <!-- a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} blockquote.smallindentedblock {margin-right: 0em; font-size: smaller} blockquote.smallquotation {font-size: smaller} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} div.lisp {margin-left: 3.2em} div.smalldisplay {margin-left: 3.2em} div.smallexample {margin-left: 3.2em} div.smalllisp {margin-left: 3.2em} kbd {font-style: oblique} pre.display {font-family: inherit} pre.format {font-family: inherit} pre.menu-comment {font-family: serif} pre.menu-preformatted {font-family: serif} pre.smalldisplay {font-family: inherit; font-size: smaller} pre.smallexample {font-size: smaller} pre.smallformat {font-family: inherit; font-size: smaller} pre.smalllisp {font-size: smaller} span.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} ul.no-bullet {list-style: none} --> </style> </head> <body lang="en"> <a name="atof"></a> <div class="header"> <p> 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> </div> <hr> <a name="atof_002c-atoff_002d_002d_002dstring-to-double-or-float"></a> <h3 class="section">2.7 <code>atof</code>, <code>atoff</code>—string to double or float</h3> <a name="index-atof"></a> <a name="index-atoff"></a> <p><strong>Synopsis</strong> </p><div class="example"> <pre class="example">#include <stdlib.h> double atof(const char *<var>s</var>); float atoff(const char *<var>s</var>); </pre></div> <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> <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: </p><div class="smallexample"> <pre class="smallexample"> [+|-]<var>digits</var>[.][<var>digits</var>][(e|E)[+|-]<var>digits</var>] </pre></div> <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> <p><code>atof(<var>s</var>)</code> is implemented as <code>strtod(<var>s</var>, NULL)</code>. <code>atoff(<var>s</var>)</code> is implemented as <code>strtof(<var>s</var>, NULL)</code>. </p> <br> <p><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> <p><code>atoff</code> obeys the same rules as <code>atof</code>, except that it returns a <code>float</code>. </p> <br> <p><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> <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> <hr> <div class="header"> <p> 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> </div> </body> </html>