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219 lines
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219 lines
11 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This manual describes how to install and use the GNU multiple precision
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arithmetic library, version 6.1.0.
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Copyright 1991, 1993-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document under
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the terms of the GNU Free Documentation License, Version 1.3 or any later
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version published by the Free Software Foundation; with no Invariant Sections,
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with the Front-Cover Texts being "A GNU Manual", and with the Back-Cover
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Texts being "You have freedom to copy and modify this GNU Manual, like GNU
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software". A copy of the license is included in
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GNU Free Documentation License. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Formatted Input Strings (GNU MP 6.1.0)</title>
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<meta name="description" content="How to install and use the GNU multiple precision arithmetic library, version 6.1.0.">
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<meta name="keywords" content="Formatted Input Strings (GNU MP 6.1.0)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="Formatted-Input.html#Formatted-Input" rel="up" title="Formatted Input">
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<link href="Formatted-Input-Functions.html#Formatted-Input-Functions" rel="next" title="Formatted Input Functions">
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<link href="Formatted-Input.html#Formatted-Input" rel="prev" title="Formatted Input">
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</head>
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<body lang="en">
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<a name="Formatted-Input-Strings"></a>
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<div class="header">
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<p>
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Next: <a href="Formatted-Input-Functions.html#Formatted-Input-Functions" accesskey="n" rel="next">Formatted Input Functions</a>, Previous: <a href="Formatted-Input.html#Formatted-Input" accesskey="p" rel="prev">Formatted Input</a>, Up: <a href="Formatted-Input.html#Formatted-Input" accesskey="u" rel="up">Formatted Input</a> [<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Formatted-Input-Strings-1"></a>
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<h3 class="section">11.1 Formatted Input Strings</h3>
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<p><code>gmp_scanf</code> and friends accept format strings similar to the standard C
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<code>scanf</code> (see <a href="http://www.gnu.org/software/libc/manual/html_node/Formatted-Input.html#Formatted-Input">Formatted Input</a> in <cite>The GNU C
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Library Reference Manual</cite>). A format specification is of the form
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</p>
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<div class="example">
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<pre class="example">% [flags] [width] [type] conv
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</pre></div>
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<p>GMP adds types ‘<samp>Z</samp>’, ‘<samp>Q</samp>’ and ‘<samp>F</samp>’ for <code>mpz_t</code>, <code>mpq_t</code>
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and <code>mpf_t</code> respectively. ‘<samp>Z</samp>’ and ‘<samp>Q</samp>’ behave like integers.
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‘<samp>Q</samp>’ will read a ‘<samp>/</samp>’ and a denominator, if present. ‘<samp>F</samp>’ behaves
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like a float.
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</p>
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<p>GMP variables don’t require an <code>&</code> when passed to <code>gmp_scanf</code>, since
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they’re already “call-by-reference”. For example,
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</p>
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<div class="example">
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<pre class="example">/* to read say "a(5) = 1234" */
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int n;
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mpz_t z;
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gmp_scanf ("a(%d) = %Zd\n", &n, z);
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mpq_t q1, q2;
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gmp_sscanf ("0377 + 0x10/0x11", "%Qi + %Qi", q1, q2);
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/* to read say "topleft (1.55,-2.66)" */
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mpf_t x, y;
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char buf[32];
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gmp_scanf ("%31s (%Ff,%Ff)", buf, x, y);
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</pre></div>
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<p>All the standard C <code>scanf</code> types behave the same as in the C library
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<code>scanf</code>, and can be freely intermixed with the GMP extensions. In the
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current implementation the standard parts of the format string are simply
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handed to <code>scanf</code> and only the GMP extensions handled directly.
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</p>
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<p>The flags accepted are as follows. ‘<samp>a</samp>’ and ‘<samp>'</samp>’ will depend on
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support from the C library, and ‘<samp>'</samp>’ cannot be used with GMP types.
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</p>
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<blockquote>
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<table>
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<tr><td><code>*</code></td><td>read but don’t store</td></tr>
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<tr><td><code>a</code></td><td>allocate a buffer (string conversions)</td></tr>
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<tr><td><code>'</code></td><td>grouped digits, GLIBC style (not GMP types)</td></tr>
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</table>
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</blockquote>
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<p>The standard types accepted are as follows. ‘<samp>h</samp>’ and ‘<samp>l</samp>’ are
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portable, the rest will depend on the compiler (or include files) for the type
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and the C library for the input.
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</p>
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<blockquote>
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<table>
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<tr><td><code>h</code></td><td><code>short</code></td></tr>
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<tr><td><code>hh</code></td><td><code>char</code></td></tr>
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<tr><td><code>j</code></td><td><code>intmax_t</code> or <code>uintmax_t</code></td></tr>
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<tr><td><code>l</code></td><td><code>long int</code>, <code>double</code> or <code>wchar_t</code></td></tr>
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<tr><td><code>ll</code></td><td><code>long long</code></td></tr>
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<tr><td><code>L</code></td><td><code>long double</code></td></tr>
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<tr><td><code>q</code></td><td><code>quad_t</code> or <code>u_quad_t</code></td></tr>
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<tr><td><code>t</code></td><td><code>ptrdiff_t</code></td></tr>
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<tr><td><code>z</code></td><td><code>size_t</code></td></tr>
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</table>
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</blockquote>
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<p>The GMP types are
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</p>
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<blockquote>
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<table>
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<tr><td><code>F</code></td><td><code>mpf_t</code>, float conversions</td></tr>
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<tr><td><code>Q</code></td><td><code>mpq_t</code>, integer conversions</td></tr>
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<tr><td><code>Z</code></td><td><code>mpz_t</code>, integer conversions</td></tr>
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</table>
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</blockquote>
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<p>The conversions accepted are as follows. ‘<samp>p</samp>’ and ‘<samp>[</samp>’ will depend on
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support from the C library, the rest are standard.
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</p>
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<blockquote>
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<table>
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<tr><td><code>c</code></td><td>character or characters</td></tr>
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<tr><td><code>d</code></td><td>decimal integer</td></tr>
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<tr><td><code>e</code> <code>E</code> <code>f</code> <code>g</code> <code>G</code></td><td>float</td></tr>
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<tr><td><code>i</code></td><td>integer with base indicator</td></tr>
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<tr><td><code>n</code></td><td>characters read so far</td></tr>
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<tr><td><code>o</code></td><td>octal integer</td></tr>
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<tr><td><code>p</code></td><td>pointer</td></tr>
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<tr><td><code>s</code></td><td>string of non-whitespace characters</td></tr>
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<tr><td><code>u</code></td><td>decimal integer</td></tr>
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<tr><td><code>x</code> <code>X</code></td><td>hex integer</td></tr>
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<tr><td><code>[</code></td><td>string of characters in a set</td></tr>
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</table>
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</blockquote>
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<p>‘<samp>e</samp>’, ‘<samp>E</samp>’, ‘<samp>f</samp>’, ‘<samp>g</samp>’ and ‘<samp>G</samp>’ are identical, they all
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read either fixed point or scientific format, and either upper or lower case
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‘<samp>e</samp>’ for the exponent in scientific format.
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</p>
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<p>C99 style hex float format (<code>printf %a</code>, see <a href="Formatted-Output-Strings.html#Formatted-Output-Strings">Formatted Output Strings</a>) is always accepted for <code>mpf_t</code>, but for the standard float
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types it will depend on the C library.
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</p>
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<p>‘<samp>x</samp>’ and ‘<samp>X</samp>’ are identical, both accept both upper and lower case
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hexadecimal.
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</p>
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<p>‘<samp>o</samp>’, ‘<samp>u</samp>’, ‘<samp>x</samp>’ and ‘<samp>X</samp>’ all read positive or negative
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values. For the standard C types these are described as “unsigned”
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conversions, but that merely affects certain overflow handling, negatives are
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still allowed (per <code>strtoul</code>, see <a href="http://www.gnu.org/software/libc/manual/html_node/Parsing-of-Integers.html#Parsing-of-Integers">Parsing of
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Integers</a> in <cite>The GNU C Library Reference Manual</cite>). For GMP types there are
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no overflows, so ‘<samp>d</samp>’ and ‘<samp>u</samp>’ are identical.
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</p>
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<p>‘<samp>Q</samp>’ type reads the numerator and (optional) denominator as given. If the
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value might not be in canonical form then <code>mpq_canonicalize</code> must be
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called before using it in any calculations (see <a href="Rational-Number-Functions.html#Rational-Number-Functions">Rational Number Functions</a>).
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</p>
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<p>‘<samp>Qi</samp>’ will read a base specification separately for the numerator and
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denominator. For example ‘<samp>0x10/11</samp>’ would be 16/11, whereas
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‘<samp>0x10/0x11</samp>’ would be 16/17.
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</p>
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<p>‘<samp>n</samp>’ can be used with any of the types above, even the GMP types.
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‘<samp>*</samp>’ to suppress assignment is allowed, though in that case it would do
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nothing at all.
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</p>
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<p>Other conversions or types that might be accepted by the C library
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<code>scanf</code> cannot be used through <code>gmp_scanf</code>.
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</p>
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<p>Whitespace is read and discarded before a field, except for ‘<samp>c</samp>’ and
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‘<samp>[</samp>’ conversions.
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</p>
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<p>For float conversions, the decimal point character (or string) expected is
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taken from the current locale settings on systems which provide
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<code>localeconv</code> (see <a href="http://www.gnu.org/software/libc/manual/html_node/Locales.html#Locales">Locales and Internationalization</a> in <cite>The GNU C Library Reference Manual</cite>). The C library will normally do the same
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for standard float input.
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</p>
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<p>The format string is only interpreted as plain <code>char</code>s, multibyte
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characters are not recognised. Perhaps this will change in the future.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Formatted-Input-Functions.html#Formatted-Input-Functions" accesskey="n" rel="next">Formatted Input Functions</a>, Previous: <a href="Formatted-Input.html#Formatted-Input" accesskey="p" rel="prev">Formatted Input</a>, Up: <a href="Formatted-Input.html#Formatted-Input" accesskey="u" rel="up">Formatted Input</a> [<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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