boost-react-native-bundle

<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>User's Guide</title> <link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> <link rel="up" href="../ratio.html" title="Chapter 25. Boost.Ratio 2.1.0"> <link rel="prev" href="../ratio.html" title="Chapter 25. Boost.Ratio 2.1.0"> <link rel="next" href="reference.html" title="Reference"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> <td align="center"><a href="../../../index.html">Home</a></td> <td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="../ratio.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../ratio.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="reference.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> </div> <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 class="toc"> <dt><a href="users_guide.html#ratio.users_guide.getting_started">Getting Started</a></dt> <dt><a href="users_guide.html#ratio.users_guide.tutorial">Tutorial</a></dt> <dt><a href="users_guide.html#ratio.users_guide.Examples">Example</a></dt> <dt><a href="users_guide.html#ratio.users_guide.ext_references">External Resources</a></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 class="toc"><dt><a href="users_guide.html#ratio.users_guide.getting_started.install">Installing Ratio</a></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> <h6> <a name="ratio.users_guide.getting_started.install.h0"></a> <a name="ratio.users_guide.getting_started.install.getting_boost_ratio_"></a><a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.getting_boost_ratio_">Getting Boost.Ratio </a> </h6> Boost.Ratio is in the latest Boost release in the folder <code class="computeroutput">/boost/ratio</code>. Documentation, tests and examples folder are at <code class="computeroutput">boost/libs/ratio/</code>. 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">boost/ratio</code> and <code class="computeroutput">libs/ratio</code>. 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. <h6> <a name="ratio.users_guide.getting_started.install.h1"></a> <a name="ratio.users_guide.getting_started.install.where_to_install_boost_ratio__"></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> The simple way is to decompress (or checkout from SVN) the files in your BOOST_ROOT directory. <h6> <a name="ratio.users_guide.getting_started.install.h2"></a> <a name="ratio.users_guide.getting_started.install.building_boost_ratio_"></a><a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.building_boost_ratio_">Building Boost.Ratio </a> </h6> Boost.Ratio is a header only library, so no need to compile anything, you just need to <code class="computeroutput">include <boost/ratio.hpp></code>. <h6> <a name="ratio.users_guide.getting_started.install.h3"></a> <a name="ratio.users_guide.getting_started.install.requirements"></a><a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.requirements">Requirements</a> </h6> Boost.Ratio 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). In particular, Boost.Ratio depends on: <div class="variablelist"> <dl class="variablelist"> <dt><a href="http://www.boost.org/libs/config" target="_top">Boost.Config</a></dt> <dd> for configuration purposes, ... </dd> <dt><a href="http://www.boost.org/libs/integer" target="_top">Boost.Integer</a></dt> <dd> for cstdint conformance, and integer traits ... </dd> <dt><a href="http://www.boost.org/libs/mpl" target="_top">Boost.MPL</a></dt> <dd> for MPL Assert and bool, logical ... </dd> <dt><a href="http://www.boost.org/libs/static_assert" target="_top">Boost.StaticAssert</a></dt> <dd> for STATIC_ASSERT, ... </dd> <dt><a href="http://www.boost.org/libs/type_traits" target="_top">Boost.TypeTraits</a></dt> <dd> for is_base, is_convertible ... </dd> <dt><a href="http://www.boost.org/libs/utility" target="_top">Boost.Utility/EnableIf</a></dt> <dd> for enable_if, ... </dd> </dl> </div> <h6> <a name="ratio.users_guide.getting_started.install.h4"></a> <a name="ratio.users_guide.getting_started.install.building_an_executable_that_uses__emphasis_role__bold__boost_ratio__emphasis__"></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 Boost.Ratio </a> </h6> No link is needed. <h6> <a name="ratio.users_guide.getting_started.install.h5"></a> <a name="ratio.users_guide.getting_started.install.exception_safety_"></a><a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.exception_safety_">Exception safety </a> </h6> All functions in the library are exception-neutral, providing the strong exception safety guarantee. <h6> <a name="ratio.users_guide.getting_started.install.h6"></a> <a name="ratio.users_guide.getting_started.install.thread_safety_"></a><a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.thread_safety_">Thread safety </a> </h6> All functions in the library are thread-unsafe except when noted explicitly. <h6> <a name="ratio.users_guide.getting_started.install.h7"></a> <a name="ratio.users_guide.getting_started.install.tested_compilers_"></a><a class="link" href="users_guide.html#ratio.users_guide.getting_started.install.tested_compilers_">Tested compilers </a> </h6> Boost.Ratio should work with an C++03 conforming compiler. The current version has been tested on: Windows with <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> MSVC 10.0 </li></ul></div> MinGW with <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> GCC 4.5.0 </li> <li class="listitem"> GCC 4.5.0 -std=c++0x </li> <li class="listitem"> GCC 4.5.2 </li> <li class="listitem"> GCC 4.5.2 -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> Ubuntu with * GCC 4.4.6 * GCC 4.4.6 -std=c++0x * GCC 4.5.4 * GCC 4.5.4 -std=c++0x * GCC 4.6.1 * GCC 4.6.1 -std=c++0x * Intel 12.1.3 * Intel 12.1.3 -std=c++0x OsX with <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> GCC 4.1.2 </li> <li class="listitem"> GCC 4.6.2 </li> <li class="listitem"> GCC 4.6.2 -std=c++0x </li> <li class="listitem"> GCC 4.7.0 </li> <li class="listitem"> GCC 4.7.0 -std=c++0x </li> <li class="listitem"> GCC 4.7.1 </li> <li class="listitem"> GCC 4.7.1 -std=c++0x </li> <li class="listitem"> clang 1.6 </li> <li class="listitem"> clang 2.9 </li> <li class="listitem"> clang 2.9 -std=c++0x </li> <li class="listitem"> clang 3.0 </li> <li class="listitem"> clang 3.0 -std=c++0x </li> <li class="listitem"> clang 3.1 </li> <li class="listitem"> clang 3.1 -std=c++0x </li> <li class="listitem"> clang 3.1 -std=c++0x -stdlib=libc++ </li> <li class="listitem"> clang 3.2 </li> <li class="listitem"> clang 3.2 -std=c++11 </li> <li class="listitem"> clang 3.2 -std=c++11 -stdlib=libc++ </li> </ul></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"> Please let us know how this works on other platforms/compilers. </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"> Please send any questions, comments and bug reports to boost <at> lists <dot> boost <dot> org. </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> <h5> <a name="ratio.users_guide.tutorial.h0"></a> <a name="ratio.users_guide.tutorial.ratio"></a><a class="link" href="users_guide.html#ratio.users_guide.tutorial.ratio">Ratio</a> </h5> <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</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">ratio</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">time_point</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">ratio</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">ratio</code></a> arithmetic) are always reduced to the lowest terms. <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a> is a template taking two <code class="computeroutput">intmax_ts</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">static const intmax_t</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">ratio</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">ratio</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. Example: <pre class="programlisting">typedef <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a><5, 3> five_thirds; // five_thirds::num == 5, five_thirds::den == 3 typedef <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a><25, 15> also_five_thirds; // also_five_thirds::num == 5, also_five_thirds::den == 3 typedef ratio_divide<five_thirds, also_five_thirds>::type one; // one::num == 1, one::den == 1 </pre> 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">atto</code></a> through <a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput">exa</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">ratio</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. Example: <pre class="programlisting">typedef ratio_multiply<<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a><5>, giga>::type _5giga; // _5giga::num == 5000000000, _5giga::den == 1 typedef ratio_multiply<<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a><5>, nano>::type _5nano; // _5nano::num == 1, _5nano::den == 200000000 </pre> <h5> <a name="ratio.users_guide.tutorial.h1"></a> <a name="ratio.users_guide.tutorial.ratio_i_o"></a><a class="link" href="users_guide.html#ratio.users_guide.tutorial.ratio_i_o">Ratio I/O</a> </h5> For each <code class="computeroutput">ratio<N, D></code> there exists a <code class="computeroutput">ratio_string<ratio<N, D>, CharT></code> for which you can query two strings: <code class="computeroutput">symbol</code> and <code class="computeroutput">prefix</code>. For those <code class="computeroutput">ratio</code>'s that correspond to an <a href="http://en.wikipedia.org/wiki/SI_prefix#List_of_SI_prefixes" target="_top">SI prefix</a> prefix corresponds to the internationally recognized prefix, stored as a <code class="computeroutput">basic_string<CharT></code>. For example <code class="computeroutput">ratio_string<mega, char>::prefix()</code> returns <code class="computeroutput">string("mega")</code>. For those <code class="computeroutput">ratio</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">symbol</code> corresponds to the internationally recognized symbol, stored as a <code class="computeroutput">basic_string<CharT></code>. For example, <code class="computeroutput">ratio_string<mega, char>::symbol()</code> returns <code class="computeroutput">string("M")</code>. For all other <code class="computeroutput">ratio</code>s, both <code class="computeroutput">prefix()</code> and <code class="computeroutput">symbol()</code> return a <code class="computeroutput">basic_string</code> containing "[<code class="computeroutput">ratio::num/ratio::den</code>]". <code class="computeroutput">ratio_string<ratio<N, D>, CharT></code> is only defined for four character types: <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> <code class="computeroutput">char</code>: UTF-8 </li> <li class="listitem"> <code class="computeroutput">char16_t</code>: UTF-16 </li> <li class="listitem"> <code class="computeroutput">char32_t</code>: UTF-32 </li> <li class="listitem"> <code class="computeroutput">wchar_t</code>: UTF-16 (if wchar_t is 16 bits) or UTF-32 </li> </ul></div> When the character is char, UTF-8 will be used to encode the names. When the character is <code class="computeroutput">char16_t</code>, UTF-16 will be used to encode the names. When the character is <code class="computeroutput">char32_t</code>, UTF-32 will be used to encode the names. When the character is <code class="computeroutput">wchar_t</code>, the encoding will be UTF-16 if <code class="computeroutput">wchar_t</code> is 16 bits, and otherwise UTF-32. The <code class="computeroutput">symbol</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. Examples: <pre class="programlisting">#include <boost/ratio/ratio_io.hpp> #include <iostream> int main() { using namespace std; using namespace boost; cout << "ratio_string<deca, char>::prefix() = " << ratio_string<deca, char>::prefix() << '\n'; cout << "ratio_string<deca, char>::symbol() = " << ratio_string<deca, char>::symbol() << '\n'; cout << "ratio_string<giga, char>::prefix() = " << ratio_string<giga, char>::prefix() << '\n'; cout << "ratio_string<giga, char>::symbol() = " << ratio_string<giga, char>::symbol() << '\n'; cout << "ratio_string<ratio<4, 6>, char>::prefix() = " << ratio_string<ratio<4, 6>, char>::prefix() << '\n'; cout << "ratio_string<ratio<4, 6>, char>::symbol() = " << ratio_string<ratio<4, 6>, char>::symbol() << '\n'; } </pre> The output will be <pre class="programlisting">ratio_string<deca, char>::prefix() = deca ratio_string<deca, char>::symbol() = da ratio_string<giga, char>::prefix() = giga ratio_string<giga, char>::symbol() = G ratio_string<ratio<4, 6>, char>::prefix() = [2/3] ratio_string<ratio<4, 6>, char>::symbol() = [2/3] </pre> <h5> <a name="ratio.users_guide.tutorial.h2"></a> <a name="ratio.users_guide.tutorial.ratio_mpl_numeric_metafunctions"></a><a class="link" href="users_guide.html#ratio.users_guide.tutorial.ratio_mpl_numeric_metafunctions">Ratio MPL Numeric Metafunctions</a> </h5> 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 Boost.MPL Integral Constants in the same expression, as in <pre class="programlisting">typedef mpl::times<int_<5>, giga>::type _5giga; // _5giga::num == 5000000000, _5giga::den == 1 typedef mpl::times<int_<5>, nano>::type _5nano; // _5nano::num == 1, _5nano::den == 200000000 </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 class="toc"><dt><a href="users_guide.html#ratio.users_guide.Examples.si_units">SI units</a></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> This example illustrates the use of type-safe physics code interoperating with <code class="computeroutput">boost::chrono::duration</code> types, taking advantage of the Boost.Ratio infrastructure and design philosophy. Let's start by defining a <code class="computeroutput">length</code> class template that mimics <code class="computeroutput">boost::chrono::duration</code>, which represents a time duration in various units, but restricts the representation to <code class="computeroutput">double</code> and uses Boost.Ratio for length unit conversions: <pre class="programlisting">template <class Ratio> class length { private: double len_; public: typedef Ratio ratio; length() : len_(1) {} length(const double& len) : len_(len) {} template <class R> length(const length<R>& d) : len_(d.count() * boost::ratio_divide<Ratio, R>::type::den / boost::ratio_divide<Ratio, R>::type::num) {} double count() const {return len_;} length& operator+=(const length& d) {len_ += d.count(); return *this;} length& operator-=(const length& d) {len_ -= d.count(); return *this;} length operator+() const {return *this;} length operator-() const {return length(-len_);} length& operator*=(double rhs) {len_ *= rhs; return *this;} length& operator/=(double rhs) {len_ /= rhs; return *this;} }; </pre> Here's a small sampling of length units: <pre class="programlisting">typedef length<boost::<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a><1> > meter; // set meter as "unity" typedef length<boost::<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput">centi</code></a>> centimeter; // 1/100 meter typedef length<boost::<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio_si_typedefs" title="SI typedefs"><code class="computeroutput">kilo</code></a>> kilometer; // 1000 meters typedef length<boost::<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a><254, 10000> > inch; // 254/10000 meters </pre> Note that since <code class="computeroutput">length</code>'s template parameter is actually a generic ratio type, so we can use boost::ratio allowing for more complex length units: <pre class="programlisting">typedef length<boost::ratio_multiply<boost::<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a><12>, inch::<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a>>::type> foot; // 12 inchs typedef length<boost::ratio_multiply<boost::<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a><5280>, foot::<a class="link" href="reference.html#ratio.reference.std.ratio_hpp.ratio" title="Class Template ratio<>"><code class="computeroutput">ratio</code></a>>::type> mile; // 5280 feet </pre> Now we need a floating point-based definition of seconds: <pre class="programlisting">typedef boost::chrono::duration<double> seconds; // unity </pre> We can even support sub-nanosecond durations: <pre class="programlisting">typedef boost::chrono::duration<double, boost::<a class="link" href="re