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<a name="Formatted-Output-Strings"></a>
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<p>
Next: <a href="Formatted-Output-Functions.html#Formatted-Output-Functions" accesskey="n" rel="next">Formatted Output Functions</a>, Previous: <a href="Formatted-Output.html#Formatted-Output" accesskey="p" rel="prev">Formatted Output</a>, Up: <a href="Formatted-Output.html#Formatted-Output" accesskey="u" rel="up">Formatted Output</a> [<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Format-Strings"></a>
<h3 class="section">10.1 Format Strings</h3>
<p><code>gmp_printf</code> and friends accept format strings similar to the standard C
<code>printf</code> (see <a href="http://www.gnu.org/software/libc/manual/html_node/Formatted-Output.html#Formatted-Output">Formatted Output</a> in <cite>The GNU C
Library Reference Manual</cite>). A format specification is of the form
</p>
<div class="example">
<pre class="example">% [flags] [width] [.[precision]] [type] conv
</pre></div>
<p>GMP adds types ‘<samp>Z</samp>’, ‘<samp>Q</samp>’ and ‘<samp>F</samp>’ for <code>mpz_t</code>, <code>mpq_t</code>
and <code>mpf_t</code> respectively, ‘<samp>M</samp>’ for <code>mp_limb_t</code>, and ‘<samp>N</samp>’ for
an <code>mp_limb_t</code> array. ‘<samp>Z</samp>’, ‘<samp>Q</samp>’, ‘<samp>M</samp>’ and ‘<samp>N</samp>’ behave
like integers. ‘<samp>Q</samp>’ will print a ‘<samp>/</samp>’ and a denominator, if needed.
‘<samp>F</samp>’ behaves like a float. For example,
</p>
<div class="example">
<pre class="example">mpz_t z;
gmp_printf ("%s is an mpz %Zd\n", "here", z);
mpq_t q;
gmp_printf ("a hex rational: %#40Qx\n", q);
mpf_t f;
int n;
gmp_printf ("fixed point mpf %.*Ff with %d digits\n", n, f, n);
mp_limb_t l;
gmp_printf ("limb %Mu\n", l);
const mp_limb_t *ptr;
mp_size_t size;
gmp_printf ("limb array %Nx\n", ptr, size);
</pre></div>
<p>For ‘<samp>N</samp>’ the limbs are expected least significant first, as per the
<code>mpn</code> functions (see <a href="Low_002dlevel-Functions.html#Low_002dlevel-Functions">Low-level Functions</a>). A negative size can be
given to print the value as a negative.
</p>
<p>All the standard C <code>printf</code> types behave the same as the C library
<code>printf</code>, and can be freely intermixed with the GMP extensions. In the
current implementation the standard parts of the format string are simply
handed to <code>printf</code> and only the GMP extensions handled directly.
</p>
<p>The flags accepted are as follows. GLIBC style ‘<samp>'</samp>’ is only for the
standard C types (not the GMP types), and only if the C library supports it.
</p>
<blockquote>
<table>
<tr><td><code>0</code></td><td>pad with zeros (rather than spaces)</td></tr>
<tr><td><code>#</code></td><td>show the base with ‘<samp>0x</samp>’, ‘<samp>0X</samp>’ or ‘<samp>0</samp>’</td></tr>
<tr><td><code>+</code></td><td>always show a sign</td></tr>
<tr><td>(space)</td><td>show a space or a ‘<samp>-</samp>’ sign</td></tr>
<tr><td><code>'</code></td><td>group digits, GLIBC style (not GMP types)</td></tr>
</table>
</blockquote>
<p>The optional width and precision can be given as a number within the format
string, or as a ‘<samp>*</samp>’ to take an extra parameter of type <code>int</code>, the
same as the standard <code>printf</code>.
</p>
<p>The standard types accepted are as follows. ‘<samp>h</samp>’ and ‘<samp>l</samp>’ are
portable, the rest will depend on the compiler (or include files) for the type
and the C library for the output.
</p>
<blockquote>
<table>
<tr><td><code>h</code></td><td><code>short</code></td></tr>
<tr><td><code>hh</code></td><td><code>char</code></td></tr>
<tr><td><code>j</code></td><td><code>intmax_t</code> or <code>uintmax_t</code></td></tr>
<tr><td><code>l</code></td><td><code>long</code> or <code>wchar_t</code></td></tr>
<tr><td><code>ll</code></td><td><code>long long</code></td></tr>
<tr><td><code>L</code></td><td><code>long double</code></td></tr>
<tr><td><code>q</code></td><td><code>quad_t</code> or <code>u_quad_t</code></td></tr>
<tr><td><code>t</code></td><td><code>ptrdiff_t</code></td></tr>
<tr><td><code>z</code></td><td><code>size_t</code></td></tr>
</table>
</blockquote>
<p>The GMP types are
</p>
<blockquote>
<table>
<tr><td><code>F</code></td><td><code>mpf_t</code>, float conversions</td></tr>
<tr><td><code>Q</code></td><td><code>mpq_t</code>, integer conversions</td></tr>
<tr><td><code>M</code></td><td><code>mp_limb_t</code>, integer conversions</td></tr>
<tr><td><code>N</code></td><td><code>mp_limb_t</code> array, integer conversions</td></tr>
<tr><td><code>Z</code></td><td><code>mpz_t</code>, integer conversions</td></tr>
</table>
</blockquote>
<p>The conversions accepted are as follows. ‘<samp>a</samp>’ and ‘<samp>A</samp>’ are always
supported for <code>mpf_t</code> but depend on the C library for standard C float
types. ‘<samp>m</samp>’ and ‘<samp>p</samp>’ depend on the C library.
</p>
<blockquote>
<table>
<tr><td><code>a</code> <code>A</code></td><td>hex floats, C99 style</td></tr>
<tr><td><code>c</code></td><td>character</td></tr>
<tr><td><code>d</code></td><td>decimal integer</td></tr>
<tr><td><code>e</code> <code>E</code></td><td>scientific format float</td></tr>
<tr><td><code>f</code></td><td>fixed point float</td></tr>
<tr><td><code>i</code></td><td>same as <code>d</code></td></tr>
<tr><td><code>g</code> <code>G</code></td><td>fixed or scientific float</td></tr>
<tr><td><code>m</code></td><td><code>strerror</code> string, GLIBC style</td></tr>
<tr><td><code>n</code></td><td>store characters written so far</td></tr>
<tr><td><code>o</code></td><td>octal integer</td></tr>
<tr><td><code>p</code></td><td>pointer</td></tr>
<tr><td><code>s</code></td><td>string</td></tr>
<tr><td><code>u</code></td><td>unsigned integer</td></tr>
<tr><td><code>x</code> <code>X</code></td><td>hex integer</td></tr>
</table>
</blockquote>
<p>‘<samp>o</samp>’, ‘<samp>x</samp>’ and ‘<samp>X</samp>’ are unsigned for the standard C types, but for
types ‘<samp>Z</samp>’, ‘<samp>Q</samp>’ and ‘<samp>N</samp>’ they are signed. ‘<samp>u</samp>’ is not
meaningful for ‘<samp>Z</samp>’, ‘<samp>Q</samp>’ and ‘<samp>N</samp>’.
</p>
<p>‘<samp>M</samp>’ is a proxy for the C library ‘<samp>l</samp>’ or ‘<samp>L</samp>’, according to the
size of <code>mp_limb_t</code>. Unsigned conversions will be usual, but a signed
conversion can be used and will interpret the value as a twos complement
negative.
</p>
<p>‘<samp>n</samp>’ can be used with any type, even the GMP types.
</p>
<p>Other types or conversions that might be accepted by the C library
<code>printf</code> cannot be used through <code>gmp_printf</code>, this includes for
instance extensions registered with GLIBC <code>register_printf_function</code>.
Also currently there’s no support for POSIX ‘<samp>$</samp>’ style numbered arguments
(perhaps this will be added in the future).
</p>
<p>The precision field has its usual meaning for integer ‘<samp>Z</samp>’ and float
‘<samp>F</samp>’ types, but is currently undefined for ‘<samp>Q</samp>’ and should not be used
with that.
</p>
<p><code>mpf_t</code> conversions only ever generate as many digits as can be
accurately represented by the operand, the same as <code>mpf_get_str</code> does.
Zeros will be used if necessary to pad to the requested precision. This
happens even for an ‘<samp>f</samp>’ conversion of an <code>mpf_t</code> which is an
integer, for instance <em>2^1024<!-- /@w --></em> in an <code>mpf_t</code> of 128 bits
precision will only produce about 40 digits, then pad with zeros to the
decimal point. An empty precision field like ‘<samp>%.Fe</samp>’ or ‘<samp>%.Ff</samp>’ can
be used to specifically request just the significant digits. Without any dot
and thus no precision field, a precision value of 6 will be used. Note that
these rules mean that ‘<samp>%Ff</samp>’, ‘<samp>%.Ff</samp>’, and ‘<samp>%.0Ff</samp>’ will all be
different.
</p>
<p>The decimal point character (or string) is taken from the current locale
settings on systems which provide <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 for standard float output.
</p>
<p>The format string is only interpreted as plain <code>char</code>s, multibyte
characters are not recognised. Perhaps this will change in the future.
</p>
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