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| <div class="section"> |
| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> |
| <a name="ratio.users_guide"></a><a class="link" href="users_guide.html" title="User's Guide">User's Guide</a> |
| </h2></div></div></div> |
| <div class="toc"><dl> |
| <dt><span class="section"><a href="users_guide.html#ratio.users_guide.getting_started">Getting Started</a></span></dt> |
| <dt><span class="section"><a href="users_guide.html#ratio.users_guide.tutorial">Tutorial</a></span></dt> |
| <dt><span class="section"><a href="users_guide.html#ratio.users_guide.Examples">Example</a></span></dt> |
| <dt><span class="section"><a href="users_guide.html#ratio.users_guide.ext_references">External Resources</a></span></dt> |
| </dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="ratio.users_guide.getting_started"></a><a class="link" href="users_guide.html#ratio.users_guide.getting_started" title="Getting Started">Getting Started</a> |
| </h3></div></div></div> |
| <div class="toc"><dl><dt><span class="section"><a href="users_guide.html#ratio.users_guide.getting_started.install">Installing |
| Ratio</a></span></dt></dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="ratio.users_guide.getting_started.install"></a><a class="link" href="users_guide.html#ratio.users_guide.getting_started.install" title="Installing Ratio">Installing |
| Ratio</a> |
| </h4></div></div></div> |
| <a name="ratio.users_guide.getting_started.install.getting_boost_ratio_"></a><h6> |
| <a name="ratio.users_guide.getting_started.install.getting_boost_ratio_-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.getting_boost_ratio_">Getting |
| Boost.Ratio </a> |
| </h6> |
| <p> |
| Boost.Ratio is in the latest Boost release in the folder <code class="computeroutput"><span class="special">/</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">ratio</span></code>. |
| Documentation, tests and examples folder are at <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">libs</span><span class="special">/</span><span class="identifier">ratio</span><span class="special">/</span></code>. |
| </p> |
| <p> |
| You can also access the latest (unstable?) state from the <a href="http://svn.boost.org/svn/boost/trunk" target="_top">Boost |
| trunk</a> directories <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">ratio</span></code> |
| and <code class="computeroutput"><span class="identifier">libs</span><span class="special">/</span><span class="identifier">ratio</span></code>. |
| </p> |
| <p> |
| Just go to <a href="http://svn.boost.org/trac/boost/wiki/BoostSubversion" target="_top">the |
| wiki</a> and follow the instructions there for anonymous SVN access. |
| </p> |
| <a name="ratio.users_guide.getting_started.install.where_to_install_boost_ratio__"></a><h6> |
| <a name="ratio.users_guide.getting_started.install.where_to_install_boost_ratio__-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.where_to_install_boost_ratio__">Where |
| to install Boost.Ratio? </a> |
| </h6> |
| <p> |
| The simple way is to decompress (or checkout from SVN) the files in your |
| BOOST_ROOT directory. |
| </p> |
| <a name="ratio.users_guide.getting_started.install.building_boost_ratio_"></a><h6> |
| <a name="ratio.users_guide.getting_started.install.building_boost_ratio_-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.building_boost_ratio_">Building |
| Boost.Ratio </a> |
| </h6> |
| <p> |
| <span class="bold"><strong>Boost.Ratio</strong></span> is a header only library, |
| so no need to compile anything, you just need to <code class="computeroutput"><span class="identifier">include</span> |
| <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">ratio</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>. |
| </p> |
| <a name="ratio.users_guide.getting_started.install.requirements"></a><h6> |
| <a name="ratio.users_guide.getting_started.install.requirements-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.requirements">Requirements</a> |
| </h6> |
| <p> |
| <span class="bold"><strong>Boost.Ratio</strong></span> depends on some Boost libraries. |
| For these specific parts you must use either Boost version 1.39.0 or later |
| (even older versions may work). |
| </p> |
| <p> |
| In particular, <span class="bold"><strong>Boost.Ratio</strong></span> depends on: |
| </p> |
| <div class="variablelist"> |
| <p class="title"><b></b></p> |
| <dl> |
| <dt><span class="term"><a href="http://www.boost.org/libs/config" target="_top"><span class="bold"><strong>Boost.Config</strong></span></a></span></dt> |
| <dd><p> |
| for configuration purposes, ... |
| </p></dd> |
| <dt><span class="term"><a href="http://www.boost.org/libs/integer" target="_top"><span class="bold"><strong>Boost.Integer</strong></span></a></span></dt> |
| <dd><p> |
| for cstdint conformance, and integer traits ... |
| </p></dd> |
| <dt><span class="term"><a href="http://www.boost.org/libs/mpl" target="_top"><span class="bold"><strong>Boost.MPL</strong></span></a></span></dt> |
| <dd><p> |
| for MPL Assert and bool, logical ... |
| </p></dd> |
| <dt><span class="term"><a href="http://www.boost.org/libs/static_assert" target="_top"><span class="bold"><strong>Boost.StaticAssert</strong></span></a></span></dt> |
| <dd><p> |
| for STATIC_ASSERT, ... |
| </p></dd> |
| <dt><span class="term"><a href="http://www.boost.org/libs/type_traits" target="_top"><span class="bold"><strong>Boost.TypeTraits</strong></span></a></span></dt> |
| <dd><p> |
| for is_base, is_convertible ... |
| </p></dd> |
| <dt><span class="term"><a href="http://www.boost.org/libs/utility" target="_top"><span class="bold"><strong>Boost.Utility/EnableIf</strong></span></a></span></dt> |
| <dd><p> |
| for enable_if, ... |
| </p></dd> |
| </dl> |
| </div> |
| <a name="ratio.users_guide.getting_started.install.building_an_executable_that_uses__emphasis_role__bold__boost_ratio__emphasis__"></a><h6> |
| <a name="ratio.users_guide.getting_started.install.building_an_executable_that_uses__emphasis_role__bold__boost_ratio__emphasis__-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.building_an_executable_that_uses__emphasis_role__bold__boost_ratio__emphasis__">Building |
| an executable that uses <span class="bold"><strong>Boost.Ratio</strong></span> </a> |
| </h6> |
| <p> |
| No link is needed. |
| </p> |
| <a name="ratio.users_guide.getting_started.install.exception_safety_"></a><h6> |
| <a name="ratio.users_guide.getting_started.install.exception_safety_-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.exception_safety_">Exception |
| safety </a> |
| </h6> |
| <p> |
| All functions in the library are exception-neutral, providing the strong |
| exception safety guarantee. |
| </p> |
| <a name="ratio.users_guide.getting_started.install.thread_safety_"></a><h6> |
| <a name="ratio.users_guide.getting_started.install.thread_safety_-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.thread_safety_">Thread |
| safety </a> |
| </h6> |
| <p> |
| All functions in the library are thread-unsafe except when noted explicitly. |
| </p> |
| <a name="ratio.users_guide.getting_started.install.tested_compilers_"></a><h6> |
| <a name="ratio.users_guide.getting_started.install.tested_compilers_-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.tested_compilers_">Tested |
| compilers </a> |
| </h6> |
| <p> |
| <span class="bold"><strong>Boost.Ratio</strong></span> should work with an C++03 |
| conforming compiler. The current version has been tested on: |
| </p> |
| <p> |
| Windows with |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| MSVC 10.0 |
| </li> |
| <li class="listitem"> |
| MSVC 9.0 Express |
| </li> |
| <li class="listitem"> |
| MSVC 8.0 |
| </li> |
| </ul></div> |
| <p> |
| Cygwin 1.5 with |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| GCC 3.4.4 |
| </li></ul></div> |
| <p> |
| Cygwin 1.7 with |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"> |
| GCC 4.3.4 |
| </li></ul></div> |
| <p> |
| MinGW with |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| GCC 4.4.0 |
| </li> |
| <li class="listitem"> |
| GCC 4.5.0 |
| </li> |
| <li class="listitem"> |
| GCC 4.5.0 -std=c++0x |
| </li> |
| <li class="listitem"> |
| GCC 4.6.0 |
| </li> |
| <li class="listitem"> |
| GCC 4.6.0 -std=c++0x |
| </li> |
| </ul></div> |
| <p> |
| Ubuntu 10.10 |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| GCC 4.4.5 |
| </li> |
| <li class="listitem"> |
| GCC 4.4.5 -std=c++0x |
| </li> |
| <li class="listitem"> |
| GCC 4.5.1 |
| </li> |
| <li class="listitem"> |
| GCC 4.5.1 -std=c++0x |
| </li> |
| <li class="listitem"> |
| clang 2.8 |
| </li> |
| </ul></div> |
| <p> |
| Initial versions were tested on: |
| </p> |
| <p> |
| MacOS with GCC 4.2.4 |
| </p> |
| <p> |
| Ubuntu Linux with GCC 4.2.4 |
| </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> |
| Please let us know how this works on other platforms/compilers. |
| </p></td></tr> |
| </table></div> |
| <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> |
| Please send any questions, comments and bug reports to boost <at> |
| lists <dot> boost <dot> org. |
| </p></td></tr> |
| </table></div> |
| </div> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="ratio.users_guide.tutorial"></a><a class="link" href="users_guide.html#ratio.users_guide.tutorial" title="Tutorial">Tutorial</a> |
| </h3></div></div></div> |
| <a name="ratio.users_guide.tutorial.ratio"></a><h5> |
| <a name="ratio.users_guide.tutorial.ratio-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.tutorial.ratio">Ratio</a> |
| </h5> |
| <p> |
| <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a> |
| is a general purpose utility inspired by Walter Brown allowing one to easily |
| and safely compute rational values at compile-time. The <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a> class catches all errors (such |
| as divide by zero and overflow) at compile time. It is used in the duration |
| and <code class="computeroutput"><span class="identifier">time_point</span></code> classes to |
| efficiently create units of time. It can also be used in other "quantity" |
| libraries or anywhere there is a rational constant which is known at compile-time. |
| The use of this utility can greatly reduce the chances of run-time overflow |
| because the <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a> (and any ratios resulting |
| from <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a> |
| arithmetic) are always reduced to the lowest terms. |
| </p> |
| <p> |
| <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a> |
| is a template taking two <code class="computeroutput"><span class="identifier">intmax_ts</span></code>, |
| with the second defaulted to 1. In addition to copy constructors and assignment, |
| it only has two public members, both of which are <code class="computeroutput"><span class="keyword">static</span> |
| <span class="keyword">const</span> <span class="identifier">intmax_t</span></code>. |
| One is the numerator of the <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a> and the other is the denominator. |
| The <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a> |
| is always normalized such that it is expressed in lowest terms, and the denominator |
| is always positive. When the numerator is 0, the denominator is always 1. |
| </p> |
| <p> |
| <span class="bold"><strong>Example:</strong></span> |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">5</span><span class="special">,</span> <span class="number">3</span><span class="special">></span> <span class="identifier">five_thirds</span><span class="special">;</span> |
| <span class="comment">// five_thirds::num == 5, five_thirds::den == 3</span> |
| |
| <span class="keyword">typedef</span> <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">25</span><span class="special">,</span> <span class="number">15</span><span class="special">></span> <span class="identifier">also_five_thirds</span><span class="special">;</span> |
| <span class="comment">// also_five_thirds::num == 5, also_five_thirds::den == 3</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">ratio_divide</span><span class="special"><</span><span class="identifier">five_thirds</span><span class="special">,</span> <span class="identifier">also_five_thirds</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">one</span><span class="special">;</span> |
| <span class="comment">// one::num == 1, one::den == 1</span> |
| </pre> |
| <p> |
| This facility also includes convenience typedefs for the SI prefixes <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput"><span class="identifier">atto</span></code></a> |
| through <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput"><span class="identifier">exa</span></code></a> corresponding to their internationally |
| recognized definitions (in terms of <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a>). This is a tremendous syntactic |
| convenience. It will prevent errors in specifying constants as one no longer |
| has to double count the number of zeros when trying to write millions or |
| billions. |
| </p> |
| <p> |
| <span class="bold"><strong>Example:</strong></span> |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">ratio_multiply</span><span class="special"><</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">5</span><span class="special">>,</span> <span class="identifier">giga</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">_5giga</span><span class="special">;</span> |
| <span class="comment">// _5giga::num == 5000000000, _5giga::den == 1</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">ratio_multiply</span><span class="special"><</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">5</span><span class="special">>,</span> <span class="identifier">nano</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">_5nano</span><span class="special">;</span> |
| <span class="comment">// _5nano::num == 1, _5nano::den == 200000000</span> |
| </pre> |
| <a name="ratio.users_guide.tutorial.ratio_i_o"></a><h5> |
| <a name="ratio.users_guide.tutorial.ratio_i_o-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.tutorial.ratio_i_o">Ratio I/O</a> |
| </h5> |
| <p> |
| For each <code class="computeroutput"><span class="identifier">ratio</span><span class="special"><</span><span class="identifier">N</span><span class="special">,</span> <span class="identifier">D</span><span class="special">></span></code> there exists a <code class="computeroutput"><span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">ratio</span><span class="special"><</span><span class="identifier">N</span><span class="special">,</span> |
| <span class="identifier">D</span><span class="special">>,</span> |
| <span class="identifier">CharT</span><span class="special">></span></code> |
| for which you can query two strings: <code class="computeroutput"><span class="identifier">short_name</span></code> |
| and <code class="computeroutput"><span class="identifier">long_name</span></code>. For those |
| <code class="computeroutput"><span class="identifier">ratio</span></code>'s that correspond to |
| an <a href="http://en.wikipedia.org/wiki/SI_prefix#List_of_SI_prefixes" target="_top">SI |
| prefix</a> long_name corresponds to the internationally recognized prefix, |
| stored as a <code class="computeroutput"><span class="identifier">basic_string</span><span class="special"><</span><span class="identifier">CharT</span><span class="special">></span></code>. For example <code class="computeroutput"><span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">mega</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">long_name</span><span class="special">()</span></code> |
| returns <code class="computeroutput"><span class="identifier">string</span><span class="special">(</span><span class="string">"mega"</span><span class="special">)</span></code>. |
| For those <code class="computeroutput"><span class="identifier">ratio</span></code>s that correspond |
| to an <a href="http://en.wikipedia.org/wiki/SI_prefix#List_of_SI_prefixes" target="_top">SI |
| prefix</a> <code class="computeroutput"><span class="identifier">short_name</span></code> |
| corresponds to the internationally recognized symbol, stored as a <code class="computeroutput"><span class="identifier">basic_string</span><span class="special"><</span><span class="identifier">CharT</span><span class="special">></span></code>. |
| For example, <code class="computeroutput"><span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">mega</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">short_name</span><span class="special">()</span></code> |
| returns <code class="computeroutput"><span class="identifier">string</span><span class="special">(</span><span class="string">"M"</span><span class="special">)</span></code>. |
| For all other <code class="computeroutput"><span class="identifier">ratio</span></code>s, both |
| <code class="computeroutput"><span class="identifier">long_name</span><span class="special">()</span></code> |
| and <code class="computeroutput"><span class="identifier">short_name</span><span class="special">()</span></code> |
| return a <code class="computeroutput"><span class="identifier">basic_string</span></code> containing |
| "[<code class="computeroutput"><span class="identifier">ratio</span><span class="special">::</span><span class="identifier">num</span><span class="special">/</span><span class="identifier">ratio</span><span class="special">::</span><span class="identifier">den</span></code>]". |
| </p> |
| <p> |
| <code class="computeroutput"><span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">ratio</span><span class="special"><</span><span class="identifier">N</span><span class="special">,</span> <span class="identifier">D</span><span class="special">>,</span> <span class="identifier">CharT</span><span class="special">></span></code> is only defined for four character types: |
| </p> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="keyword">char</span></code>: UTF-8 |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="identifier">char16_t</span></code>: UTF-16 |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="identifier">char32_t</span></code>: UTF-32 |
| </li> |
| <li class="listitem"> |
| <code class="computeroutput"><span class="keyword">wchar_t</span></code>: UTF-16 (if wchar_t |
| is 16 bits) or UTF-32 |
| </li> |
| </ul></div> |
| <p> |
| When the character is char, UTF-8 will be used to encode the names. When |
| the character is <code class="computeroutput"><span class="identifier">char16_t</span></code>, |
| UTF-16 will be used to encode the names. When the character is <code class="computeroutput"><span class="identifier">char32_t</span></code>, UTF-32 will be used to encode |
| the names. When the character is <code class="computeroutput"><span class="keyword">wchar_t</span></code>, |
| the encoding will be UTF-16 if <code class="computeroutput"><span class="keyword">wchar_t</span></code> |
| is 16 bits, and otherwise UTF-32. |
| </p> |
| <p> |
| The <code class="computeroutput"><span class="identifier">short_name</span></code> (Greek mu |
| or μ) for micro is defined by <a href="http://www.unicode.org/charts/PDF/U0080.pdf" target="_top">Unicode</a> |
| to be U+00B5. |
| </p> |
| <p> |
| <span class="bold"><strong>Examples:</strong></span> |
| </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">ratio</span><span class="special">/</span><span class="identifier">ratio_io</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">iostream</span><span class="special">></span> |
| |
| <span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">std</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">;</span> |
| |
| <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"ratio_string<deca, char>::long_name() = "</span> |
| <span class="special"><<</span> <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">deca</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">long_name</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"ratio_string<deca, char>::short_name() = "</span> |
| <span class="special"><<</span> <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">deca</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">short_name</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| |
| <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"ratio_string<giga, char>::long_name() = "</span> |
| <span class="special"><<</span> <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">giga</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">long_name</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"ratio_string<giga, char>::short_name() = "</span> |
| <span class="special"><<</span> <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">giga</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">short_name</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| |
| <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"ratio_string<ratio<4, 6>, char>::long_name() = "</span> |
| <span class="special"><<</span> <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">ratio</span><span class="special"><</span><span class="number">4</span><span class="special">,</span> <span class="number">6</span><span class="special">>,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">long_name</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"ratio_string<ratio<4, 6>, char>::short_name() = "</span> |
| <span class="special"><<</span> <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">ratio</span><span class="special"><</span><span class="number">4</span><span class="special">,</span> <span class="number">6</span><span class="special">>,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">short_name</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| The output will be |
| </p> |
| <pre class="programlisting"><span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">deca</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">long_name</span><span class="special">()</span> <span class="special">=</span> <span class="identifier">deca</span> |
| <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">deca</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">short_name</span><span class="special">()</span> <span class="special">=</span> <span class="identifier">da</span> |
| <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">giga</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">long_name</span><span class="special">()</span> <span class="special">=</span> <span class="identifier">giga</span> |
| <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">giga</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">short_name</span><span class="special">()</span> <span class="special">=</span> <span class="identifier">G</span> |
| <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">ratio</span><span class="special"><</span><span class="number">4</span><span class="special">,</span> <span class="number">6</span><span class="special">>,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">long_name</span><span class="special">()</span> <span class="special">=</span> <span class="special">[</span><span class="number">2</span><span class="special">/</span><span class="number">3</span><span class="special">]</span> |
| <span class="identifier">ratio_string</span><span class="special"><</span><span class="identifier">ratio</span><span class="special"><</span><span class="number">4</span><span class="special">,</span> <span class="number">6</span><span class="special">>,</span> <span class="keyword">char</span><span class="special">>::</span><span class="identifier">short_name</span><span class="special">()</span> <span class="special">=</span> <span class="special">[</span><span class="number">2</span><span class="special">/</span><span class="number">3</span><span class="special">]</span> |
| </pre> |
| <a name="ratio.users_guide.tutorial.ratio_mpl_numeric_metafunctions"></a><h5> |
| <a name="ratio.users_guide.tutorial.ratio_mpl_numeric_metafunctions-heading"></a> |
| <a class="link" href="users_guide.html#ratio.users_guide.tutorial.ratio_mpl_numeric_metafunctions">Ratio |
| MPL Numeric Metafunctions</a> |
| </h5> |
| <p> |
| With the view of the _ratio class as a <a class="link" href="reference.html#ratio.reference.mpl.rational_constant" title="Rational Constant Concept">Rational |
| Constant</a> we can mix _ratio<> and <span class="bold"><strong>Boost.MPL</strong></span> |
| Integral Constants in the same expression, as in |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">times</span><span class="special"><</span><span class="identifier">int_</span><span class="special"><</span><span class="number">5</span><span class="special">>,</span> <span class="identifier">giga</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">_5giga</span><span class="special">;</span> |
| <span class="comment">// _5giga::num == 5000000000, _5giga::den == 1</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">times</span><span class="special"><</span><span class="identifier">int_</span><span class="special"><</span><span class="number">5</span><span class="special">>,</span> <span class="identifier">nano</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">_5nano</span><span class="special">;</span> |
| <span class="comment">// _5nano::num == 1, _5nano::den == 200000000</span> |
| </pre> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="ratio.users_guide.Examples"></a><a class="link" href="users_guide.html#ratio.users_guide.Examples" title="Example">Example</a> |
| </h3></div></div></div> |
| <div class="toc"><dl><dt><span class="section"><a href="users_guide.html#ratio.users_guide.Examples.si_units">SI units</a></span></dt></dl></div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="ratio.users_guide.Examples.si_units"></a><a class="link" href="users_guide.html#ratio.users_guide.Examples.si_units" title="SI units">SI units</a> |
| </h4></div></div></div> |
| <p> |
| This example illustrates the use of type-safe physics code interoperating |
| with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span></code> types, taking advantage of the |
| <span class="bold"><strong>Boost.Ratio</strong></span> infrastructure and design |
| philosophy. |
| </p> |
| <p> |
| Let's start by defining a <code class="computeroutput"><span class="identifier">length</span></code> |
| class template that mimics <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span></code>, |
| which represents a time duration in various units, but restricts the representation |
| to <code class="computeroutput"><span class="keyword">double</span></code> and uses <span class="bold"><strong>Boost.Ratio</strong></span> for length unit conversions: |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Ratio</span><span class="special">></span> |
| <span class="keyword">class</span> <span class="identifier">length</span> <span class="special">{</span> |
| <span class="keyword">private</span><span class="special">:</span> |
| <span class="keyword">double</span> <span class="identifier">len_</span><span class="special">;</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="keyword">typedef</span> <span class="identifier">Ratio</span> <span class="identifier">ratio</span><span class="special">;</span> |
| <span class="identifier">length</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">len_</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{}</span> |
| <span class="identifier">length</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">double</span><span class="special">&</span> <span class="identifier">len</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">len_</span><span class="special">(</span><span class="identifier">len</span><span class="special">)</span> <span class="special">{}</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> |
| <span class="identifier">length</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">length</span><span class="special"><</span><span class="identifier">R</span><span class="special">>&</span> <span class="identifier">d</span><span class="special">)</span> |
| <span class="special">:</span> <span class="identifier">len_</span><span class="special">(</span><span class="identifier">d</span><span class="special">.</span><span class="identifier">count</span><span class="special">()</span> <span class="special">*</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_divide</span><span class="special"><</span><span class="identifier">Ratio</span><span class="special">,</span> <span class="identifier">R</span><span class="special">>::</span><span class="identifier">type</span><span class="special">::</span><span class="identifier">den</span> <span class="special">/</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_divide</span><span class="special"><</span><span class="identifier">Ratio</span><span class="special">,</span> <span class="identifier">R</span><span class="special">>::</span><span class="identifier">type</span><span class="special">::</span><span class="identifier">num</span><span class="special">)</span> <span class="special">{}</span> |
| |
| <span class="keyword">double</span> <span class="identifier">count</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span><span class="keyword">return</span> <span class="identifier">len_</span><span class="special">;}</span> |
| |
| <span class="identifier">length</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">+=(</span><span class="keyword">const</span> <span class="identifier">length</span><span class="special">&</span> <span class="identifier">d</span><span class="special">)</span> <span class="special">{</span><span class="identifier">len_</span> <span class="special">+=</span> <span class="identifier">d</span><span class="special">.</span><span class="identifier">count</span><span class="special">();</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;}</span> |
| <span class="identifier">length</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">-=(</span><span class="keyword">const</span> <span class="identifier">length</span><span class="special">&</span> <span class="identifier">d</span><span class="special">)</span> <span class="special">{</span><span class="identifier">len_</span> <span class="special">-=</span> <span class="identifier">d</span><span class="special">.</span><span class="identifier">count</span><span class="special">();</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;}</span> |
| |
| <span class="identifier">length</span> <span class="keyword">operator</span><span class="special">+()</span> <span class="keyword">const</span> <span class="special">{</span><span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;}</span> |
| <span class="identifier">length</span> <span class="keyword">operator</span><span class="special">-()</span> <span class="keyword">const</span> <span class="special">{</span><span class="keyword">return</span> <span class="identifier">length</span><span class="special">(-</span><span class="identifier">len_</span><span class="special">);}</span> |
| |
| <span class="identifier">length</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">*=(</span><span class="keyword">double</span> <span class="identifier">rhs</span><span class="special">)</span> <span class="special">{</span><span class="identifier">len_</span> <span class="special">*=</span> <span class="identifier">rhs</span><span class="special">;</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;}</span> |
| <span class="identifier">length</span><span class="special">&</span> <span class="keyword">operator</span><span class="special">/=(</span><span class="keyword">double</span> <span class="identifier">rhs</span><span class="special">)</span> <span class="special">{</span><span class="identifier">len_</span> <span class="special">/=</span> <span class="identifier">rhs</span><span class="special">;</span> <span class="keyword">return</span> <span class="special">*</span><span class="keyword">this</span><span class="special">;}</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| Here's a small sampling of length units: |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">length</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">></span> <span class="special">></span> <span class="identifier">meter</span><span class="special">;</span> <span class="comment">// set meter as "unity"</span> |
| <span class="keyword">typedef</span> <span class="identifier">length</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput"><span class="identifier">centi</span></code></a><span class="special">></span> <span class="identifier">centimeter</span><span class="special">;</span> <span class="comment">// 1/100 meter</span> |
| <span class="keyword">typedef</span> <span class="identifier">length</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput"><span class="identifier">kilo</span></code></a><span class="special">></span> <span class="identifier">kilometer</span><span class="special">;</span> <span class="comment">// 1000 meters</span> |
| <span class="keyword">typedef</span> <span class="identifier">length</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">254</span><span class="special">,</span> <span class="number">10000</span><span class="special">></span> <span class="special">></span> <span class="identifier">inch</span><span class="special">;</span> <span class="comment">// 254/10000 meters</span> |
| </pre> |
| <p> |
| Note that since <code class="computeroutput"><span class="identifier">length</span></code>'s |
| template parameter is actually a generic ratio type, so we can use boost::ratio |
| allowing for more complex length units: |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">length</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_multiply</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">12</span><span class="special">>,</span> <span class="identifier">inch</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special">>::</span><span class="identifier">type</span><span class="special">></span> <span class="identifier">foot</span><span class="special">;</span> <span class="comment">// 12 inchs</span> |
| <span class="keyword">typedef</span> <span class="identifier">length</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_multiply</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">5280</span><span class="special">>,</span> <span class="identifier">foot</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special">>::</span><span class="identifier">type</span><span class="special">></span> <span class="identifier">mile</span><span class="special">;</span> <span class="comment">// 5280 feet</span> |
| </pre> |
| <p> |
| Now we need a floating point-based definition of seconds: |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">seconds</span><span class="special">;</span> <span class="comment">// unity</span> |
| </pre> |
| <p> |
| We can even support sub-nanosecond durations: |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput"><span class="identifier">pico</span></code></a><span class="special">></span> <span class="identifier">picosecond</span><span class="special">;</span> <span class="comment">// 10^-12 seconds</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput"><span class="identifier">femto</span></code></a><span class="special">></span> <span class="identifier">femtosecond</span><span class="special">;</span> <span class="comment">// 10^-15 seconds</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">duration</span><span class="special"><</span><span class="keyword">double</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput"><span class="identifier">atto</span></code></a><span class="special">></span> <span class="identifier">attosecond</span><span class="special">;</span> <span class="comment">// 10^-18 seconds</span> |
| </pre> |
| <p> |
| Finally, we can write a proof-of-concept of an SI units library, hard-wired |
| for meters and floating point seconds, though it will accept other units: |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">R1</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R2</span><span class="special">></span> |
| <span class="keyword">class</span> <span class="identifier">quantity</span> |
| <span class="special">{</span> |
| <span class="keyword">double</span> <span class="identifier">q_</span><span class="special">;</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="keyword">typedef</span> <span class="identifier">R1</span> <span class="identifier">time_dim</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">R2</span> <span class="identifier">distance_dim</span><span class="special">;</span> |
| <span class="identifier">quantity</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">q_</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{}</span> |
| |
| <span class="keyword">double</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span><span class="keyword">return</span> <span class="identifier">q_</span><span class="special">;}</span> |
| <span class="keyword">void</span> <span class="identifier">set</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">q</span><span class="special">)</span> <span class="special">{</span><span class="identifier">q_</span> <span class="special">=</span> <span class="identifier">q</span><span class="special">;}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">template</span> <span class="special"><></span> |
| <span class="keyword">class</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">></span> <span class="special">></span> |
| <span class="special">{</span> |
| <span class="keyword">double</span> <span class="identifier">q_</span><span class="special">;</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="identifier">quantity</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">q_</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{}</span> |
| <span class="identifier">quantity</span><span class="special">(</span><span class="identifier">seconds</span> <span class="identifier">d</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">q_</span><span class="special">(</span><span class="identifier">d</span><span class="special">.</span><span class="identifier">count</span><span class="special">())</span> <span class="special">{}</span> <span class="comment">// note: only User1::seconds needed here</span> |
| |
| <span class="keyword">double</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span><span class="keyword">return</span> <span class="identifier">q_</span><span class="special">;}</span> |
| <span class="keyword">void</span> <span class="identifier">set</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">q</span><span class="special">)</span> <span class="special">{</span><span class="identifier">q_</span> <span class="special">=</span> <span class="identifier">q</span><span class="special">;}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">template</span> <span class="special"><></span> |
| <span class="keyword">class</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">></span> <span class="special">></span> |
| <span class="special">{</span> |
| <span class="keyword">double</span> <span class="identifier">q_</span><span class="special">;</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="identifier">quantity</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">q_</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{}</span> |
| <span class="identifier">quantity</span><span class="special">(</span><span class="identifier">meter</span> <span class="identifier">d</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">q_</span><span class="special">(</span><span class="identifier">d</span><span class="special">.</span><span class="identifier">count</span><span class="special">())</span> <span class="special">{}</span> <span class="comment">// note: only User1::meter needed here</span> |
| |
| <span class="keyword">double</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span><span class="keyword">return</span> <span class="identifier">q_</span><span class="special">;}</span> |
| <span class="keyword">void</span> <span class="identifier">set</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">q</span><span class="special">)</span> <span class="special">{</span><span class="identifier">q_</span> <span class="special">=</span> <span class="identifier">q</span><span class="special">;}</span> |
| <span class="special">};</span> |
| |
| <span class="keyword">template</span> <span class="special"><></span> |
| <span class="keyword">class</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">></span> <span class="special">></span> |
| <span class="special">{</span> |
| <span class="keyword">double</span> <span class="identifier">q_</span><span class="special">;</span> |
| <span class="keyword">public</span><span class="special">:</span> |
| <span class="identifier">quantity</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">q_</span><span class="special">(</span><span class="number">1</span><span class="special">)</span> <span class="special">{}</span> |
| <span class="identifier">quantity</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">d</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">q_</span><span class="special">(</span><span class="identifier">d</span><span class="special">)</span> <span class="special">{}</span> |
| |
| <span class="keyword">double</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span><span class="keyword">return</span> <span class="identifier">q_</span><span class="special">;}</span> |
| <span class="keyword">void</span> <span class="identifier">set</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">q</span><span class="special">)</span> <span class="special">{</span><span class="identifier">q_</span> <span class="special">=</span> <span class="identifier">q</span><span class="special">;}</span> |
| <span class="special">};</span> |
| </pre> |
| <p> |
| That allows us to create some useful SI-based unit types: |
| </p> |
| <pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">></span> <span class="special">></span> <span class="identifier">Scalar</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">></span> <span class="special">></span> <span class="identifier">Time</span><span class="special">;</span> <span class="comment">// second</span> |
| <span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">></span> <span class="special">></span> <span class="identifier">Distance</span><span class="special">;</span> <span class="comment">// meter</span> |
| <span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><-</span><span class="number">1</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">></span> <span class="special">></span> <span class="identifier">Speed</span><span class="special">;</span> <span class="comment">// meter/second</span> |
| <span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><-</span><span class="number">2</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">></span> <span class="special">></span> <span class="identifier">Acceleration</span><span class="special">;</span> <span class="comment">// meter/second^2</span> |
| </pre> |
| <p> |
| To make quantity useful, we need to be able to do arithmetic: |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">R1</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R2</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R3</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R4</span><span class="special">></span> |
| <span class="identifier">quantity</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_subtract</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R3</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> |
| <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_subtract</span><span class="special"><</span><span class="identifier">R2</span><span class="special">,</span> <span class="identifier">R4</span><span class="special">>::</span><span class="identifier">type</span><span class="special">></span> |
| <span class="keyword">operator</span><span class="special">/(</span><span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R3</span><span class="special">,</span> <span class="identifier">R4</span><span class="special">>&</span> <span class="identifier">y</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_subtract</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R3</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> |
| <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_subtract</span><span class="special"><</span><span class="identifier">R2</span><span class="special">,</span> <span class="identifier">R4</span><span class="special">>::</span><span class="identifier">type</span><span class="special">></span> <span class="identifier">R</span><span class="special">;</span> |
| <span class="identifier">R</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="identifier">r</span><span class="special">.</span><span class="identifier">set</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">/</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span> |
| <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">R1</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R2</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R3</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R4</span><span class="special">></span> |
| <span class="identifier">quantity</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_add</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R3</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> |
| <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_add</span><span class="special"><</span><span class="identifier">R2</span><span class="special">,</span> <span class="identifier">R4</span><span class="special">>::</span><span class="identifier">type</span><span class="special">></span> |
| <span class="keyword">operator</span><span class="special">*(</span><span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R3</span><span class="special">,</span> <span class="identifier">R4</span><span class="special">>&</span> <span class="identifier">y</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_add</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R3</span><span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> |
| <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_add</span><span class="special"><</span><span class="identifier">R2</span><span class="special">,</span> <span class="identifier">R4</span><span class="special">>::</span><span class="identifier">type</span><span class="special">></span> <span class="identifier">R</span><span class="special">;</span> |
| <span class="identifier">R</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="identifier">r</span><span class="special">.</span><span class="identifier">set</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">*</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span> |
| <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">R1</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R2</span><span class="special">></span> |
| <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">></span> |
| <span class="keyword">operator</span><span class="special">+(</span><span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">>&</span> <span class="identifier">y</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">></span> <span class="identifier">R</span><span class="special">;</span> |
| <span class="identifier">R</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="identifier">r</span><span class="special">.</span><span class="identifier">set</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span> |
| <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">R1</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">R2</span><span class="special">></span> |
| <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">></span> |
| <span class="keyword">operator</span><span class="special">-(</span><span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">>&</span> <span class="identifier">y</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">></span> <span class="identifier">R</span><span class="special">;</span> |
| <span class="identifier">R</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="identifier">r</span><span class="special">.</span><span class="identifier">set</span><span class="special">(</span><span class="identifier">x</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">-</span> <span class="identifier">y</span><span class="special">.</span><span class="identifier">get</span><span class="special">());</span> |
| <span class="keyword">return</span> <span class="identifier">r</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| With all of the foregoing scaffolding, we can now write an exemplar of |
| a type-safe physics function: |
| </p> |
| <pre class="programlisting"><span class="identifier">Distance</span> |
| <span class="identifier">compute_distance</span><span class="special">(</span><span class="identifier">Speed</span> <span class="identifier">v0</span><span class="special">,</span> <span class="identifier">Time</span> <span class="identifier">t</span><span class="special">,</span> <span class="identifier">Acceleration</span> <span class="identifier">a</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">v0</span> <span class="special">*</span> <span class="identifier">t</span> <span class="special">+</span> <span class="identifier">Scalar</span><span class="special">(.</span><span class="number">5</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">a</span> <span class="special">*</span> <span class="identifier">t</span> <span class="special">*</span> <span class="identifier">t</span><span class="special">;</span> <span class="comment">// if a units mistake is made here it won't compile</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| Finally, we can exercise what we've created, even using custom time durations |
| (<code class="computeroutput"><span class="identifier">User1</span><span class="special">::</span><span class="identifier">seconds</span></code>) as well as Boost time durations |
| (<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">hours</span></code>). The input can be in arbitrary, |
| though type-safe, units, the output is always in SI units. (A complete |
| Units library would support other units, of course.) |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">8</span><span class="special">,</span> <span class="identifier">BOOST_INTMAX_C</span><span class="special">(</span><span class="number">0</span><span class="identifier">x7FFFFFFFD</span><span class="special">)></span> <span class="identifier">R1</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">3</span><span class="special">,</span> <span class="identifier">BOOST_INTMAX_C</span><span class="special">(</span><span class="number">0</span><span class="identifier">x7FFFFFFFD</span><span class="special">)></span> <span class="identifier">R2</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">quantity</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_subtract</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">></span> <span class="special">>::</span><span class="identifier">type</span><span class="special">,</span> |
| <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_subtract</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">1</span><span class="special">>,</span> <span class="identifier">boost</span><span class="special">::</span><a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput"><span class="identifier">ratio</span></code></a><span class="special"><</span><span class="number">0</span><span class="special">></span> <span class="special">>::</span><span class="identifier">type</span> <span class="special">></span> <span class="identifier">RR</span><span class="special">;</span> |
| <span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ratio_subtract</span><span class="special"><</span><span class="identifier">R1</span><span class="special">,</span> <span class="identifier">R2</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">RS</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">RS</span><span class="special">::</span><span class="identifier">num</span> <span class="special"><<</span> <span class="char">'/'</span> <span class="special"><<</span> <span class="identifier">RS</span><span class="special">::</span><span class="identifier">den</span> <span class="special"><<</span> <span class="char">'\n'</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="string">"*************\n"</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="string">"* testUser1 *\n"</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="string">"*************\n"</span><span class="special">;</span> |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Distance</span> <span class="identifier">d</span><span class="special">(</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">mile</span><span class="special">(</span><span class="number">110</span><span class="special">)</span> <span class="special">);</span> |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Time</span> <span class="identifier">t</span><span class="special">(</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><code class="computeroutput"><span class="identifier">hours</span></code><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">);</span> |
| |
| <span class="identifier">RR</span> <span class="identifier">r</span><span class="special">=</span><span class="identifier">d</span> <span class="special">/</span> <span class="identifier">t</span><span class="special">;</span> |
| <span class="comment">//r.set(d.get() / t.get());</span> |
| |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Speed</span> <span class="identifier">rc</span><span class="special">=</span> <span class="identifier">r</span><span class="special">;</span> |
| |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Speed</span> <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">d</span> <span class="special">/</span> <span class="identifier">t</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="string">"Speed = "</span> <span class="special"><<</span> <span class="identifier">s</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special"><<</span> <span class="string">" meters/sec\n"</span><span class="special">;</span> |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Acceleration</span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Distance</span><span class="special">(</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">foot</span><span class="special">(</span><span class="number">32.2</span><span class="special">)</span> <span class="special">)</span> <span class="special">/</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Time</span><span class="special">()</span> <span class="special">/</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Time</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="string">"Acceleration = "</span> <span class="special"><<</span> <span class="identifier">a</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special"><<</span> <span class="string">" meters/sec^2\n"</span><span class="special">;</span> |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Distance</span> <span class="identifier">df</span> <span class="special">=</span> <span class="identifier">compute_distance</span><span class="special">(</span><span class="identifier">s</span><span class="special">,</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">Time</span><span class="special">(</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">0.5</span><span class="special">)</span> <span class="special">),</span> <span class="identifier">a</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="string">"Distance = "</span> <span class="special"><<</span> <span class="identifier">df</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special"><<</span> <span class="string">" meters\n"</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="string">"There are "</span> |
| <span class="special"><<</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">mile</span><span class="special">::</span><span class="identifier">ratio</span><span class="special">::</span><span class="identifier">den</span> <span class="special"><<</span> <span class="char">'/'</span> <span class="special"><<</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">mile</span><span class="special">::</span><span class="identifier">ratio</span><span class="special">::</span><span class="identifier">num</span> <span class="special"><<</span> <span class="string">" miles/meter"</span><span class="special">;</span> |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">meter</span> <span class="identifier">mt</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">mile</span> <span class="identifier">mi</span> <span class="special">=</span> <span class="identifier">mt</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="string">" which is approximately "</span> <span class="special"><<</span> <span class="identifier">mi</span><span class="special">.</span><span class="identifier">count</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'\n'</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="string">"There are "</span> |
| <span class="special"><<</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">mile</span><span class="special">::</span><span class="identifier">ratio</span><span class="special">::</span><span class="identifier">num</span> <span class="special"><<</span> <span class="char">'/'</span> <span class="special"><<</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">mile</span><span class="special">::</span><span class="identifier">ratio</span><span class="special">::</span><span class="identifier">den</span> <span class="special"><<</span> <span class="string">" meters/mile"</span><span class="special">;</span> |
| <span class="identifier">mi</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> |
| <span class="identifier">mt</span> <span class="special">=</span> <span class="identifier">mi</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="string">" which is approximately "</span> <span class="special"><<</span> <span class="identifier">mt</span><span class="special">.</span><span class="identifier">count</span><span class="special">()</span> <span class="special"><<</span> <span class="char">'\n'</span><span class="special">;</span> |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">attosecond</span> <span class="identifier">as</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> |
| <span class="identifier">User1</span><span class="special">::</span><span class="identifier">seconds</span> <span class="identifier">sec</span> <span class="special">=</span> <span class="identifier">as</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="string">"1 attosecond is "</span> <span class="special"><<</span> <span class="identifier">sec</span><span class="special">.</span><span class="identifier">count</span><span class="special">()</span> <span class="special"><<</span> <span class="string">" seconds\n"</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="string">"sec = as; // compiles\n"</span><span class="special">;</span> |
| <span class="identifier">sec</span> <span class="special">=</span> <span class="identifier">User1</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">1</span><span class="special">);</span> |
| <span class="identifier">as</span> <span class="special">=</span> <span class="identifier">sec</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="string">"1 second is "</span> <span class="special"><<</span> <span class="identifier">as</span><span class="special">.</span><span class="identifier">count</span><span class="special">()</span> <span class="special"><<</span> <span class="string">" attoseconds\n"</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="string">"as = sec; // compiles\n"</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="string">"\n"</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| <span class="emphasis"><em>See the source file <a href="../../../example/si_physics.cpp" target="_top">example/si_physics.cpp</a></em></span> |
| </p> |
| </div> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="ratio.users_guide.ext_references"></a><a class="link" href="users_guide.html#ratio.users_guide.ext_references" title="External Resources">External Resources</a> |
| </h3></div></div></div> |
| <div class="variablelist"> |
| <p class="title"><b></b></p> |
| <dl> |
| <dt><span class="term"><a href="http://www.open-std.org/jtc1/sc22/wg21" target="_top"><span class="bold"><strong>C++ |
| Standards Committee's current Working Paper</strong></span></a></span></dt> |
| <dd><p> |
| The most authoritative reference material for the library is the C++ |
| Standards Committee's current Working Paper (WP). 20.6 Compile-time |
| rational arithmetic "ratio" |
| </p></dd> |
| <dt><span class="term"><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2661.htm" target="_top"><span class="bold"><strong>N2661 - A Foundation to Sleep On</strong></span></a></span></dt> |
| <dd><p> |
| From Howard E. Hinnant, Walter E. Brown, Jeff Garland and Marc Paterno. |
| Is very informative and provides motivation for key design decisions |
| </p></dd> |
| <dt><span class="term"><a href="http://lwg.github.com/issues/lwg-defects.html#1281" target="_top"><span class="bold"><strong>LWG 1281. CopyConstruction and Assignment between ratios having |
| the same normalized form</strong></span></a></span></dt> |
| <dd><p> |
| From Vicente Juan Botet Escriba. |
| </p></dd> |
| </dl> |
| </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 © 2008 Howard Hinnant<br>Copyright © 2006, 2008 Beman Dawes<br>Copyright © 2009-2011 Vicente J. Botet |
| Escriba<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> |
| <hr> |
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