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<a name="C_002b_002b-Interface-General"></a>
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<p>
Next: <a href="C_002b_002b-Interface-Integers.html#C_002b_002b-Interface-Integers" accesskey="n" rel="next">C++ Interface Integers</a>, Previous: <a href="C_002b_002b-Class-Interface.html#C_002b_002b-Class-Interface" accesskey="p" rel="prev">C++ Class Interface</a>, Up: <a href="C_002b_002b-Class-Interface.html#C_002b_002b-Class-Interface" accesskey="u" rel="up">C++ Class Interface</a> &nbsp; [<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="C_002b_002b-Interface-General-1"></a>
<h3 class="section">12.1 C++ Interface General</h3>

<p>All the C++ classes and functions are available with
</p>
<a name="index-gmpxx_002eh"></a>
<div class="example">
<pre class="example">#include &lt;gmpxx.h&gt;
</pre></div>

<p>Programs should be linked with the <samp>libgmpxx</samp> and <samp>libgmp</samp>
libraries.  For example,
</p>
<div class="example">
<pre class="example">g++ mycxxprog.cc -lgmpxx -lgmp
</pre></div>

<p>The classes defined are
</p>
<dl>
<dt><a name="index-mpz_005fclass"></a>Class: <strong>mpz_class</strong></dt>
<dt><a name="index-mpq_005fclass"></a>Class: <strong>mpq_class</strong></dt>
<dt><a name="index-mpf_005fclass"></a>Class: <strong>mpf_class</strong></dt>
</dl>

<p>The standard operators and various standard functions are overloaded to allow
arithmetic with these classes.  For example,
</p>
<div class="example">
<pre class="example">int
main (void)
{
  mpz_class a, b, c;

  a = 1234;
  b = &quot;-5678&quot;;
  c = a+b;
  cout &lt;&lt; &quot;sum is &quot; &lt;&lt; c &lt;&lt; &quot;\n&quot;;
  cout &lt;&lt; &quot;absolute value is &quot; &lt;&lt; abs(c) &lt;&lt; &quot;\n&quot;;

  return 0;
}
</pre></div>

<p>An important feature of the implementation is that an expression like
<code>a=b+c</code> results in a single call to the corresponding <code>mpz_add</code>,
without using a temporary for the <code>b+c</code> part.  Expressions which by their
nature imply intermediate values, like <code>a=b*c+d*e</code>, still use temporaries
though.
</p>
<p>The classes can be freely intermixed in expressions, as can the classes and
the standard types <code>long</code>, <code>unsigned long</code> and <code>double</code>.
Smaller types like <code>int</code> or <code>float</code> can also be intermixed, since
C++ will promote them.
</p>
<p>Note that <code>bool</code> is not accepted directly, but must be explicitly cast to
an <code>int</code> first.  This is because C++ will automatically convert any
pointer to a <code>bool</code>, so if GMP accepted <code>bool</code> it would make all
sorts of invalid class and pointer combinations compile but almost certainly
not do anything sensible.
</p>
<p>Conversions back from the classes to standard C++ types aren&rsquo;t done
automatically, instead member functions like <code>get_si</code> are provided (see
the following sections for details).
</p>
<p>Also there are no automatic conversions from the classes to the corresponding
GMP C types, instead a reference to the underlying C object can be obtained
with the following functions,
</p>
<dl>
<dt><a name="index-mpz_005fclass_003a_003aget_005fmpz_005ft"></a>Function: <em>mpz_t</em> <strong>mpz_class::get_mpz_t</strong> <em>()</em></dt>
<dt><a name="index-mpq_005fclass_003a_003aget_005fmpq_005ft"></a>Function: <em>mpq_t</em> <strong>mpq_class::get_mpq_t</strong> <em>()</em></dt>
<dt><a name="index-mpf_005fclass_003a_003aget_005fmpf_005ft"></a>Function: <em>mpf_t</em> <strong>mpf_class::get_mpf_t</strong> <em>()</em></dt>
</dl>

<p>These can be used to call a C function which doesn&rsquo;t have a C++ class
interface.  For example to set <code>a</code> to the GCD of <code>b</code> and <code>c</code>,
</p>
<div class="example">
<pre class="example">mpz_class a, b, c;
...
mpz_gcd (a.get_mpz_t(), b.get_mpz_t(), c.get_mpz_t());
</pre></div>

<p>In the other direction, a class can be initialized from the corresponding GMP
C type, or assigned to if an explicit constructor is used.  In both cases this
makes a copy of the value, it doesn&rsquo;t create any sort of association.  For
example,
</p>
<div class="example">
<pre class="example">mpz_t z;
// ... init and calculate z ...
mpz_class x(z);
mpz_class y;
y = mpz_class (z);
</pre></div>

<p>There are no namespace setups in <samp>gmpxx.h</samp>, all types and functions are
simply put into the global namespace.  This is what <samp>gmp.h</samp> has done in
the past, and continues to do for compatibility.  The extras provided by
<samp>gmpxx.h</samp> follow GMP naming conventions and are unlikely to clash with
anything.
</p>

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<div class="header">
<p>
Next: <a href="C_002b_002b-Interface-Integers.html#C_002b_002b-Interface-Integers" accesskey="n" rel="next">C++ Interface Integers</a>, Previous: <a href="C_002b_002b-Class-Interface.html#C_002b_002b-Class-Interface" accesskey="p" rel="prev">C++ Class Interface</a>, Up: <a href="C_002b_002b-Class-Interface.html#C_002b_002b-Class-Interface" accesskey="u" rel="up">C++ Class Interface</a> &nbsp; [<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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