1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Quick Start</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../boost_units.html" title="Chapter 43. Boost.Units 1.1.0"> 10<link rel="prev" href="../boost_units.html" title="Chapter 43. Boost.Units 1.1.0"> 11<link rel="next" href="Dimensional_Analysis.html" title="Dimensional Analysis"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="../boost_units.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../boost_units.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="Dimensional_Analysis.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="boost_units.Quick_Start"></a><a class="link" href="Quick_Start.html" title="Quick Start">Quick Start</a> 29</h2></div></div></div> 30<p> 31 Before discussing the basics of the library, we first define a few terms that 32 will be used frequently in the following : 33 </p> 34<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 35<li class="listitem"> 36 <span class="bold"><strong>Base dimension</strong></span> : A base dimension is loosely 37 defined as a measurable entity of interest; in conventional dimensional 38 analysis, base dimensions include length ([L]), mass ([M]), time ([T]), 39 etc... but there is no specific restriction on what base dimensions can 40 be used. Base dimensions are essentially a tag type and provide no dimensional 41 analysis functionality themselves. 42 </li> 43<li class="listitem"> 44 <span class="bold"><strong>Dimension</strong></span> : A collection of zero or more 45 base dimensions, each potentially raised to a different rational power. 46 For example, length = [L]^1, area = [L]^2, velocity = [L]^1/[T]^1, and 47 energy = [M]^1 [L]^2/[T]^2 are all dimensions. 48 </li> 49<li class="listitem"> 50 <span class="bold"><strong>Base unit</strong></span> : A base unit represents a specific 51 measure of a dimension. For example, while length is an abstract measure 52 of distance, the meter is a concrete base unit of distance. Conversions 53 are defined using base units. Much like base dimensions, base units are 54 a tag type used solely to define units and do not support dimensional analysis 55 algebra. 56 </li> 57<li class="listitem"> 58 <span class="bold"><strong>Unit</strong></span> : A set of base units raised to rational 59 exponents, e.g. m^1, kg^1, m^1/s^2. 60 </li> 61<li class="listitem"> 62 <span class="bold"><strong>System</strong></span> : A unit system is a collection 63 of base units representing all the measurable entities of interest for 64 a specific problem. For example, the SI unit system defines seven base 65 units : length ([L]) in meters, mass ([M]) in kilograms, time ([T]) in 66 seconds, current ([I]) in amperes, temperature ([theta]) in kelvin, amount 67 ([N]) in moles, and luminous intensity ([J]) in candelas. All measurable 68 entities within the SI system can be represented as products of various 69 integer or rational powers of these seven base units. 70 </li> 71<li class="listitem"> 72 <span class="bold"><strong>Quantity</strong></span> : A quantity represents a concrete 73 amount of a unit. Thus, while the meter is the base unit of length in the 74 SI system, 5.5 meters is a quantity of length in that system. 75 </li> 76</ul></div> 77<p> 78 To begin, we present two short tutorials. <a href="../../../libs/units/tutorial/tutorial_1.cpp" target="_top">Tutorial1</a> 79 demonstrates the use of <a href="http://en.wikipedia.org/wiki/SI_units" target="_top">SI</a> 80 units. After including the appropriate system headers and the headers for the 81 various SI units we will need (all SI units can be included with <code class="computeroutput"><a class="link" href="Reference.html#header.boost.units.systems.si_hpp" title="Header <boost/units/systems/si.hpp>">boost/units/systems/si.hpp</a></code>) and 82 for quantity I/O (<code class="computeroutput"><a class="link" href="Reference.html#header.boost.units.io_hpp" title="Header <boost/units/io.hpp>">boost/units/io.hpp</a></code>), 83 we define a function that computes the work, in joules, done by exerting a 84 force in newtons over a specified distance in meters and outputs the result 85 to <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span></code>. The <span class="underline"><code class="computeroutput"><a class="link" href="../boost/units/quantity.html" title="Class template quantity">quantity</a></code></span> class accepts 86 a second template parameter as its value type; this parameter defaults to 87 <code class="computeroutput"><span class="keyword">double</span></code> if not otherwise specified. 88 To demonstrate the ease of using user-defined types in dimensional calculations, 89 we also present code for computing the complex impedance using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span></code> 90 as the value type : 91 </p> 92<p> 93</p> 94<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">complex</span><span class="special">></span> 95<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> 96 97<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">typeof</span><span class="special">/</span><span class="identifier">std</span><span class="special">/</span><span class="identifier">complex</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 98 99<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">energy</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 100<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">force</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 101<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">length</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 102<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">electric_potential</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 103<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">current</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 104<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">resistance</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 105<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">units</span><span class="special">/</span><span class="identifier">systems</span><span class="special">/</span><span class="identifier">si</span><span class="special">/</span><span class="identifier">io</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 106 107<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">units</span><span class="special">;</span> 108<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">units</span><span class="special">::</span><span class="identifier">si</span><span class="special">;</span> 109 110<span class="keyword">constexpr</span> 111<span class="identifier">quantity</span><span class="special"><</span><span class="identifier">energy</span><span class="special">></span> 112<span class="identifier">work</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">force</span><span class="special">>&</span> <span class="identifier">F</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">length</span><span class="special">>&</span> <span class="identifier">dx</span><span class="special">)</span> 113<span class="special">{</span> 114 <span class="keyword">return</span> <span class="identifier">F</span> <span class="special">*</span> <span class="identifier">dx</span><span class="special">;</span> <span class="comment">// Defines the relation: work = force * distance.</span> 115<span class="special">}</span> 116 117<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 118<span class="special">{</span> 119 <span class="comment">/// Test calculation of work.</span> 120 <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">force</span><span class="special">></span> <span class="identifier">F</span><span class="special">(</span><span class="number">2.0</span> <span class="special">*</span> <span class="identifier">newton</span><span class="special">);</span> <span class="comment">// Define a quantity of force.</span> 121 <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">length</span><span class="special">></span> <span class="identifier">dx</span><span class="special">(</span><span class="number">2.0</span> <span class="special">*</span> <span class="identifier">meter</span><span class="special">);</span> <span class="comment">// and a distance,</span> 122 <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">energy</span><span class="special">></span> <span class="identifier">E</span><span class="special">(</span><span class="identifier">work</span><span class="special">(</span><span class="identifier">F</span><span class="special">,</span><span class="identifier">dx</span><span class="special">));</span> <span class="comment">// and calculate the work done.</span> 123 124 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"F = "</span> <span class="special"><<</span> <span class="identifier">F</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> 125 <span class="special"><<</span> <span class="string">"dx = "</span> <span class="special"><<</span> <span class="identifier">dx</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> 126 <span class="special"><<</span> <span class="string">"E = "</span> <span class="special"><<</span> <span class="identifier">E</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> 127 <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 128 129 <span class="comment">/// Test and check complex quantities.</span> 130 <span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">complex</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">complex_type</span><span class="special">;</span> <span class="comment">// double real and imaginary parts.</span> 131 132 <span class="comment">// Define some complex electrical quantities.</span> 133 <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">electric_potential</span><span class="special">,</span> <span class="identifier">complex_type</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">complex_type</span><span class="special">(</span><span class="number">12.5</span><span class="special">,</span> <span class="number">0.0</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">volts</span><span class="special">;</span> 134 <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">current</span><span class="special">,</span> <span class="identifier">complex_type</span><span class="special">></span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">complex_type</span><span class="special">(</span><span class="number">3.0</span><span class="special">,</span> <span class="number">4.0</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">amperes</span><span class="special">;</span> 135 <span class="identifier">quantity</span><span class="special"><</span><span class="identifier">resistance</span><span class="special">,</span> <span class="identifier">complex_type</span><span class="special">></span> <span class="identifier">z</span> <span class="special">=</span> <span class="identifier">complex_type</span><span class="special">(</span><span class="number">1.5</span><span class="special">,</span> <span class="special">-</span><span class="number">2.0</span><span class="special">)</span> <span class="special">*</span> <span class="identifier">ohms</span><span class="special">;</span> 136 137 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"V = "</span> <span class="special"><<</span> <span class="identifier">v</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> 138 <span class="special"><<</span> <span class="string">"I = "</span> <span class="special"><<</span> <span class="identifier">i</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> 139 <span class="special"><<</span> <span class="string">"Z = "</span> <span class="special"><<</span> <span class="identifier">z</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> 140 <span class="comment">// Calculate from Ohm's law voltage = current * resistance.</span> 141 <span class="special"><<</span> <span class="string">"I * Z = "</span> <span class="special"><<</span> <span class="identifier">i</span> <span class="special">*</span> <span class="identifier">z</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> 142 <span class="comment">// Check defined V is equal to calculated.</span> 143 <span class="special"><<</span> <span class="string">"I * Z == V? "</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">boolalpha</span> <span class="special"><<</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">*</span> <span class="identifier">z</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> 144 <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 145 <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span> 146<span class="special">}</span> 147</pre> 148<p> 149 </p> 150<p> 151 The intent and function of the above code should be obvious; the output produced 152 is : 153 </p> 154<p> 155</p> 156<pre class="programlisting"><span class="identifier">F</span> <span class="special">=</span> <span class="number">2</span> <span class="identifier">N</span> 157<span class="identifier">dx</span> <span class="special">=</span> <span class="number">2</span> <span class="identifier">m</span> 158<span class="identifier">E</span> <span class="special">=</span> <span class="number">4</span> <span class="identifier">J</span> 159 160<span class="identifier">V</span> <span class="special">=</span> <span class="special">(</span><span class="number">12.5</span><span class="special">,</span><span class="number">0</span><span class="special">)</span> <span class="identifier">V</span> 161<span class="identifier">I</span> <span class="special">=</span> <span class="special">(</span><span class="number">3</span><span class="special">,</span><span class="number">4</span><span class="special">)</span> <span class="identifier">A</span> 162<span class="identifier">Z</span> <span class="special">=</span> <span class="special">(</span><span class="number">1.5</span><span class="special">,-</span><span class="number">2</span><span class="special">)</span> <span class="identifier">Ohm</span> 163<span class="identifier">I</span><span class="special">*</span><span class="identifier">Z</span> <span class="special">=</span> <span class="special">(</span><span class="number">12.5</span><span class="special">,</span><span class="number">0</span><span class="special">)</span> <span class="identifier">V</span> 164<span class="identifier">I</span><span class="special">*</span><span class="identifier">Z</span> <span class="special">==</span> <span class="identifier">V</span><span class="special">?</span> <span class="keyword">true</span> 165</pre> 166<p> 167 </p> 168<p> 169 While this library attempts to make simple dimensional computations easy to 170 code, it is in no way tied to any particular unit system (SI or otherwise). 171 Instead, it provides a highly flexible compile-time system for dimensional 172 analysis, supporting arbitrary collections of base dimensions, rational powers 173 of units, and explicit quantity conversions. It accomplishes all of this via 174 template metaprogramming techniques. With modern optimizing compilers, this 175 results in zero runtime overhead for quantity computations relative to the 176 same code without unit checking. 177 </p> 178</div> 179<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 180<td align="left"></td> 181<td align="right"><div class="copyright-footer">Copyright © 2003-2008 Matthias Christian Schabel<br>Copyright © 2007-2010 Steven 182 Watanabe<p> 183 Distributed under the Boost Software License, Version 1.0. (See accompanying 184 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>) 185 </p> 186</div></td> 187</tr></table> 188<hr> 189<div class="spirit-nav"> 190<a accesskey="p" href="../boost_units.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../boost_units.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="Dimensional_Analysis.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 191</div> 192</body> 193</html> 194
