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| </h2></div></div></div> |
| <div class="toc"><dl> |
| <dt><span class="section"><a href="tutorial.html#boost_random.tutorial.generating_integers_in_a_range">Generating |
| integers in a range</a></span></dt> |
| <dt><span class="section"><a href="tutorial.html#boost_random.tutorial.generating_integers_with_different_probabilities">Generating |
| integers with different probabilities</a></span></dt> |
| <dt><span class="section"><a href="tutorial.html#boost_random.tutorial.generating_a_random_password">Generating |
| a random password</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_random.tutorial.generating_integers_in_a_range"></a><a class="link" href="tutorial.html#boost_random.tutorial.generating_integers_in_a_range" title="Generating integers in a range">Generating |
| integers in a range</a> |
| </h3></div></div></div> |
| <p> |
| For the source of this example see <a href="../../..//libs/random/example/die.cpp" target="_top">die.cpp</a>. |
| First we include the headers we need for <code class="computeroutput"><a class="link" href="../boost/random/mt19937.html" title="Type definition mt19937">mt19937</a></code> |
| and <code class="computeroutput"><a class="link" href="../boost/random/uniform_int_distribution.html" title="Class template uniform_int_distribution">uniform_int_distribution</a></code>. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">random</span><span class="special">/</span><span class="identifier">mersenne_twister</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">random</span><span class="special">/</span><span class="identifier">uniform_int_distribution</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre> |
| <p> |
| </p> |
| <p> |
| We use <code class="computeroutput"><a class="link" href="../boost/random/mt19937.html" title="Type definition mt19937">mt19937</a></code> with the |
| default seed as a source of randomness. The numbers produced will be the |
| same every time the program is run. One common method to change this is to |
| seed with the current time (<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">time</span><span class="special">(</span><span class="number">0</span><span class="special">)</span></code> |
| defined in ctime). |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">random</span><span class="special">::</span><span class="identifier">mt19937</span> <span class="identifier">gen</span><span class="special">;</span></pre> |
| <p> |
| </p> |
| <div class="note"><table border="0" summary="Note"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td> |
| <th align="left">Note</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| We are using a <span class="emphasis"><em>global</em></span> generator object here. This |
| is important because we don't want to create a new <a class="link" href="reference.html#boost_random.reference.concepts.pseudo_random_number_generator" title="Pseudo-Random Number Generator">pseudo-random |
| number generator</a> at every call |
| </p></td></tr> |
| </table></div> |
| <p> |
| Now we can define a function that simulates an ordinary six-sided die. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">roll_die</span><span class="special">()</span> <span class="special">{</span> |
| <a class="co" name="boost_random0co" href="tutorial.html#boost_random0"><img src="../../../doc/src/images/callouts/1.png" alt="1" border="0"></a><span class="identifier">boost</span><span class="special">::</span><span class="identifier">random</span><span class="special">::</span><span class="identifier">uniform_int_distribution</span><span class="special"><></span> <span class="identifier">dist</span><span class="special">(</span><span class="number">1</span><span class="special">,</span> <span class="number">6</span><span class="special">);</span> |
| <a class="co" name="boost_random1co" href="tutorial.html#boost_random1"><img src="../../../doc/src/images/callouts/2.png" alt="2" border="0"></a><span class="keyword">return</span> <span class="identifier">dist</span><span class="special">(</span><span class="identifier">gen</span><span class="special">);</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <div class="calloutlist"><table border="0" summary="Callout list"> |
| <tr> |
| <td width="5%" valign="top" align="left"><p><a name="boost_random0"></a><a href="#boost_random0co"><img src="../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td> |
| <td valign="top" align="left"> |
| <p> |
| <code class="computeroutput"><a class="link" href="../boost/random/mt19937.html" title="Type definition mt19937">mt19937</a></code> produces |
| integers in the range [0, 2<sup>32</sup>-1]. However, we want numbers in the range |
| [1, 6]. The distribution <code class="computeroutput"><a class="link" href="../boost/random/uniform_int_distribution.html" title="Class template uniform_int_distribution">uniform_int_distribution</a></code> |
| performs this transformation. |
| </p> |
| <div class="warning"><table border="0" summary="Warning"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td> |
| <th align="left">Warning</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Contrary to common C++ usage <code class="computeroutput"><a class="link" href="../boost/random/uniform_int_distribution.html" title="Class template uniform_int_distribution">uniform_int_distribution</a></code> |
| does not take a <span class="emphasis"><em>half-open range</em></span>. Instead it takes |
| a <span class="emphasis"><em>closed range</em></span>. Given the parameters 1 and 6, |
| <code class="computeroutput"><a class="link" href="../boost/random/uniform_int_distribution.html" title="Class template uniform_int_distribution">uniform_int_distribution</a></code> |
| can can produce any of the values 1, 2, 3, 4, 5, or 6. |
| </p></td></tr> |
| </table></div> |
| </td> |
| </tr> |
| <tr> |
| <td width="5%" valign="top" align="left"><p><a name="boost_random1"></a><a href="#boost_random1co"><img src="../../../doc/src/images/callouts/2.png" alt="2" border="0"></a> </p></td> |
| <td valign="top" align="left"><p> |
| A distribution is a function object. We generate a random number by calling |
| <code class="computeroutput"><span class="identifier">dist</span></code> with the generator. |
| </p></td> |
| </tr> |
| </table></div> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_random.tutorial.generating_integers_with_different_probabilities"></a><a class="link" href="tutorial.html#boost_random.tutorial.generating_integers_with_different_probabilities" title="Generating integers with different probabilities">Generating |
| integers with different probabilities</a> |
| </h3></div></div></div> |
| <p> |
| For the source of this example see <a href="../../..//libs/random/example/weighted_die.cpp" target="_top">weighted_die.cpp</a>. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">random</span><span class="special">/</span><span class="identifier">mersenne_twister</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">random</span><span class="special">/</span><span class="identifier">discrete_distribution</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">mt19937</span> <span class="identifier">gen</span><span class="special">;</span></pre> |
| <p> |
| </p> |
| <p> |
| This time, instead of a fair die, the probability of rolling a 1 is 50% (!). |
| The other five faces are all equally likely. |
| </p> |
| <p> |
| <code class="computeroutput"><a class="link" href="../boost/random/discrete_distribution.html" title="Class template discrete_distribution">discrete_distribution</a></code> |
| works nicely here by allowing us to assign weights to each of the possible |
| outcomes. |
| </p> |
| <div class="tip"><table border="0" summary="Tip"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="../../../doc/src/images/tip.png"></td> |
| <th align="left">Tip</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| If your compiler supports <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">initializer_list</span></code>, |
| you can initialize <code class="computeroutput"><a class="link" href="../boost/random/discrete_distribution.html" title="Class template discrete_distribution">discrete_distribution</a></code> |
| directly with the weights. |
| </p></td></tr> |
| </table></div> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">double</span> <span class="identifier">probabilities</span><span class="special">[]</span> <span class="special">=</span> <span class="special">{</span> |
| <span class="number">0.5</span><span class="special">,</span> <span class="number">0.1</span><span class="special">,</span> <span class="number">0.1</span><span class="special">,</span> <span class="number">0.1</span><span class="special">,</span> <span class="number">0.1</span><span class="special">,</span> <span class="number">0.1</span> |
| <span class="special">};</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">random</span><span class="special">::</span><span class="identifier">discrete_distribution</span><span class="special"><></span> <span class="identifier">dist</span><span class="special">(</span><span class="identifier">probabilities</span><span class="special">);</span></pre> |
| <p> |
| </p> |
| <p> |
| Now define a function that simulates rolling this die. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">roll_weighted_die</span><span class="special">()</span> <span class="special">{</span> |
| <a class="co" name="boost_random2co" href="tutorial.html#boost_random2"><img src="../../../doc/src/images/callouts/1.png" alt="1" border="0"></a><span class="keyword">return</span> <span class="identifier">dist</span><span class="special">(</span><span class="identifier">gen</span><span class="special">)</span> <span class="special">+</span> <span class="number">1</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| </pre> |
| <p> |
| </p> |
| <div class="calloutlist"><table border="0" summary="Callout list"><tr> |
| <td width="5%" valign="top" align="left"><p><a name="boost_random2"></a><a href="#boost_random2co"><img src="../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td> |
| <td valign="top" align="left"><p> |
| Add 1 to make sure that the result is in the range [1,6] instead of [0,5]. |
| </p></td> |
| </tr></table></div> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_random.tutorial.generating_a_random_password"></a><a class="link" href="tutorial.html#boost_random.tutorial.generating_a_random_password" title="Generating a random password">Generating |
| a random password</a> |
| </h3></div></div></div> |
| <p> |
| For the source of this example see <a href="../../..//libs/random/example/password.cpp" target="_top">password.cpp</a>. |
| </p> |
| <p> |
| This example demonstrates generating a random 8 character password. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">random</span><span class="special">/</span><span class="identifier">random_device</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">random</span><span class="special">/</span><span class="identifier">uniform_int_distribution</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> <span class="special">{</span> |
| <a class="co" name="boost_random3co" href="tutorial.html#boost_random3"><img src="../../../doc/src/images/callouts/1.png" alt="1" border="0"></a><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">chars</span><span class="special">(</span> |
| <span class="string">"abcdefghijklmnopqrstuvwxyz"</span> |
| <span class="string">"ABCDEFGHIJKLMNOPQRSTUVWXYZ"</span> |
| <span class="string">"1234567890"</span> |
| <span class="string">"!@#$%^&*()"</span> |
| <span class="string">"`~-_=+[{]{\\|;:'\",<.>/? "</span><span class="special">);</span> |
| <a class="co" name="boost_random4co" href="tutorial.html#boost_random4"><img src="../../../doc/src/images/callouts/2.png" alt="2" border="0"></a><span class="identifier">boost</span><span class="special">::</span><span class="identifier">random</span><span class="special">::</span><span class="identifier">random_device</span> <span class="identifier">rng</span><span class="special">;</span> |
| <a class="co" name="boost_random5co" href="tutorial.html#boost_random5"><img src="../../../doc/src/images/callouts/3.png" alt="3" border="0"></a><span class="identifier">boost</span><span class="special">::</span><span class="identifier">random</span><span class="special">::</span><span class="identifier">uniform_int_distribution</span><span class="special"><></span> <span class="identifier">index_dist</span><span class="special">(</span><span class="number">0</span><span class="special">,</span> <span class="identifier">chars</span><span class="special">.</span><span class="identifier">size</span><span class="special">()</span> <span class="special">-</span> <span class="number">1</span><span class="special">);</span> |
| <span class="keyword">for</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="number">8</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="special">{</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">chars</span><span class="special">[</span><span class="identifier">index_dist</span><span class="special">(</span><span class="identifier">rng</span><span class="special">)];</span> |
| <span class="special">}</span> |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| </pre> |
| <p> |
| </p> |
| <div class="calloutlist"><table border="0" summary="Callout list"> |
| <tr> |
| <td width="5%" valign="top" align="left"><p><a name="boost_random3"></a><a href="#boost_random3co"><img src="../../../doc/src/images/callouts/1.png" alt="1" border="0"></a> </p></td> |
| <td valign="top" align="left"><p> |
| We first define the characters that we're going to allow. This is pretty |
| much just the characters on a standard keyboard. |
| </p></td> |
| </tr> |
| <tr> |
| <td width="5%" valign="top" align="left"><p><a name="boost_random4"></a><a href="#boost_random4co"><img src="../../../doc/src/images/callouts/2.png" alt="2" border="0"></a> </p></td> |
| <td valign="top" align="left"><p> |
| We use <code class="computeroutput"><a class="link" href="../boost/random/random_device.html" title="Class random_device">random_device</a></code> |
| as a source of entropy, since we want passwords that are not predictable. |
| </p></td> |
| </tr> |
| <tr> |
| <td width="5%" valign="top" align="left"><p><a name="boost_random5"></a><a href="#boost_random5co"><img src="../../../doc/src/images/callouts/3.png" alt="3" border="0"></a> </p></td> |
| <td valign="top" align="left"><p> |
| Finally we select 8 random characters from the string and print them |
| to cout. |
| </p></td> |
| </tr> |
| </table></div> |
| </div> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2000-2005 Jens Maurer<br>Copyright © 2009, 2010 Steven Watanabe<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
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