1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Defining New Constants</title> 5<link rel="stylesheet" href="../math.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Math Toolkit 2.12.0"> 8<link rel="up" href="../constants.html" title="Chapter 4. Mathematical Constants"> 9<link rel="prev" href="constants.html" title="The Mathematical Constants"> 10<link rel="next" href="constants_faq.html" title="Math Constants FAQs"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="constants.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../constants.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="constants_faq.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="math_toolkit.new_const"></a><a class="link" href="new_const.html" title="Defining New Constants">Defining New Constants</a> 28</h2></div></div></div> 29<p> 30 The library provides some helper code to assist in defining new constants; 31 the process for defining a constant called <code class="computeroutput"><span class="identifier">my_constant</span></code> 32 goes like this: 33 </p> 34<p> 35 1. <span class="bold"><strong>Define a function that calculates the value of the 36 constant</strong></span>. This should be a template function, and be placed in 37 <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">calculate_constants</span><span class="special">.</span><span class="identifier">hpp</span></code> if the 38 constant is to be added to this library, or else defined at the top of your 39 source file if not. 40 </p> 41<p> 42 The function should look like this: 43 </p> 44<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">constants</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">detail</span><span class="special">{</span> 45 46<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">Real</span><span class="special">></span> 47<span class="keyword">template</span> <span class="special"><</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">></span> 48<span class="identifier">Real</span> <span class="identifier">constant_my_constant</span><span class="special"><</span><span class="identifier">Real</span><span class="special">>::</span><span class="identifier">compute</span><span class="special">(</span><span class="identifier">BOOST_MATH_EXPLICIT_TEMPLATE_TYPE_SPEC</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">N</span><span class="special">>)))</span> 49<span class="special">{</span> 50 <span class="keyword">int</span> <span class="identifier">required_precision</span> <span class="special">=</span> <span class="identifier">N</span> <span class="special">?</span> <span class="identifier">N</span> <span class="special">:</span> <span class="identifier">tools</span><span class="special">::</span><span class="identifier">digits</span><span class="special"><</span><span class="identifier">Real</span><span class="special">>();</span> 51 <span class="identifier">Real</span> <span class="identifier">result</span> <span class="special">=</span> <span class="comment">/* value computed to required_precision bits */</span> <span class="special">;</span> 52 <span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span> 53<span class="special">}</span> 54 55<span class="special">}}}}</span> <span class="comment">// namespaces</span> 56</pre> 57<p> 58 Then define a placeholder for the constant itself: 59 </p> 60<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">constants</span><span class="special">{</span> 61 62<span class="identifier">BOOST_DEFINE_MATH_CONSTANT</span><span class="special">(</span><span class="identifier">my_constant</span><span class="special">,</span> <span class="number">0.0</span><span class="special">,</span> <span class="string">"0"</span><span class="special">);</span> 63 64<span class="special">}}}</span> 65</pre> 66<p> 67 For example, to calculate π/2, add to <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">calculate_constants</span><span class="special">.</span><span class="identifier">hpp</span></code> 68 </p> 69<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 70<span class="keyword">template</span><span class="special"><</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">></span> 71<span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">constant_half_pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">compute</span><span class="special">(</span><span class="identifier">BOOST_MATH_EXPLICIT_TEMPLATE_TYPE_SPEC</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">N</span><span class="special">>)))</span> 72<span class="special">{</span> 73 <span class="identifier">BOOST_MATH_STD_USING</span> 74 <span class="keyword">return</span> <span class="identifier">pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special"><</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">digits2</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span> <span class="special">></span> <span class="special">>()</span> <span class="special">/</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="number">2</span><span class="special">);</span> 75<span class="special">}</span> 76</pre> 77<p> 78 Then to <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">constants</span><span class="special">.</span><span class="identifier">hpp</span></code> add: 79 </p> 80<pre class="programlisting"><span class="identifier">BOOST_DEFINE_MATH_CONSTANT</span><span class="special">(</span><span class="identifier">half_pi</span><span class="special">,</span> <span class="number">0.0</span><span class="special">,</span> <span class="string">"0"</span><span class="special">);</span> <span class="comment">// Actual values are temporary, we'll replace them later.</span> 81</pre> 82<div class="note"><table border="0" summary="Note"> 83<tr> 84<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td> 85<th align="left">Note</th> 86</tr> 87<tr><td align="left" valign="top"><p> 88 Previously defined constants like pi and e can be used, but by <span class="bold"><strong>not simply calling</strong></span> <code class="computeroutput"><span class="identifier">pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span></code>; 89 specifying the precision via the policy <code class="computeroutput"><span class="identifier">pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> 90 <span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special"><</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">digits2</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span> <span class="special">></span> <span class="special">>()</span></code> 91 is essential to ensure full accuracy. 92 </p></td></tr> 93</table></div> 94<div class="warning"><table border="0" summary="Warning"> 95<tr> 96<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td> 97<th align="left">Warning</th> 98</tr> 99<tr><td align="left" valign="top"> 100<p> 101 Newly defined constants can only be used once they are included in <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">constants</span><span class="special">.</span><span class="identifier">hpp</span></code>. So 102 if you add <code class="computeroutput"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">N</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">constant_my_constant</span><span class="special">{...}</span></code>, 103 then you cannot define <code class="computeroutput"><span class="identifier">constant_my_constant</span></code> 104 until you add the temporary <code class="computeroutput"><span class="identifier">BOOST_DEFINE_MATH_CONSTANT</span><span class="special">(</span><span class="identifier">my_constant</span><span class="special">,</span> <span class="number">0.0</span><span class="special">,</span> 105 <span class="string">"0"</span><span class="special">)</span></code>. 106 Failing to do this will result in surprising compile errors: 107 </p> 108<pre class="programlisting"><span class="identifier">error</span> <span class="identifier">C2143</span><span class="special">:</span> <span class="identifier">syntax</span> <span class="identifier">error</span> <span class="special">:</span> <span class="identifier">missing</span> <span class="char">';'</span> <span class="identifier">before</span> <span class="char">'<'</span> 109<span class="identifier">error</span> <span class="identifier">C2433</span><span class="special">:</span> <span class="char">'constant_root_two_div_pi'</span> <span class="special">:</span> <span class="char">'inline'</span> <span class="keyword">not</span> <span class="identifier">permitted</span> <span class="identifier">on</span> <span class="identifier">data</span> <span class="identifier">declarations</span> 110<span class="identifier">error</span> <span class="identifier">C2888</span><span class="special">:</span> <span class="char">'T constant_root_two_div_pi'</span> <span class="special">:</span> <span class="identifier">symbol</span> <span class="identifier">cannot</span> <span class="identifier">be</span> <span class="identifier">defined</span> <span class="identifier">within</span> <span class="keyword">namespace</span> <span class="char">'detail'</span> 111<span class="identifier">error</span> <span class="identifier">C2988</span><span class="special">:</span> <span class="identifier">unrecognizable</span> <span class="keyword">template</span> <span class="identifier">declaration</span><span class="special">/</span><span class="identifier">definition</span> 112</pre> 113</td></tr> 114</table></div> 115<p> 116 2. <span class="bold"><strong>You will need an arbitrary precision type to use to 117 calculate the value</strong></span>. This library currently supports either <code class="computeroutput"><span class="identifier">cpp_float</span></code>, <code class="computeroutput"><span class="identifier">NTL</span><span class="special">::</span><span class="identifier">RR</span></code> or 118 <code class="computeroutput"><span class="identifier">mpfr_class</span></code> used via the bindings 119 in <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">bindings</span></code>. 120 The default is to use <code class="computeroutput"><span class="identifier">NTL</span><span class="special">::</span><span class="identifier">RR</span></code> unless you define an alternate macro, 121 for example, <code class="computeroutput"><span class="identifier">USE_MPFR</span></code> or <code class="computeroutput"><span class="identifier">USE_CPP_FLOAT</span></code> at the start of your program. 122 </p> 123<p> 124 3. It is necessary to link to the Boost.Regex library, and probably to your 125 chosen arbitrary precision type library. 126 </p> 127<p> 128 4. You need to add <code class="computeroutput"><span class="identifier">libs</span><span class="special">\</span><span class="identifier">math</span><span class="special">\</span><span class="identifier">include_private</span></code> 129 to your compiler's include path as the needed header is not installed in the 130 usual places by default (this avoids a cyclic dependency between the Math and 131 Multiprecision library's headers). 132 </p> 133<p> 134 5. The complete program to generate the constant <code class="computeroutput"><span class="identifier">half_pi</span></code> 135 using function <code class="computeroutput"><span class="identifier">calculate_half_pi</span></code> 136 is then: 137 </p> 138<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">USE_CPP_FLOAT</span> <span class="comment">// If required.</span> 139<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">generate</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 140 141<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> 142<span class="special">{</span> 143 <span class="identifier">BOOST_CONSTANTS_GENERATE</span><span class="special">(</span><span class="identifier">half_pi</span><span class="special">);</span> 144<span class="special">}</span> 145</pre> 146<p> 147 The output from the program is a snippet of C++ code (actually a macro call) 148 that can be cut and pasted into <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">constants</span><span class="special">/</span><span class="identifier">constants</span><span class="special">.</span><span class="identifier">hpp</span></code> or else into your own code, for example: 149 </p> 150<pre class="programlisting"> BOOST_DEFINE_MATH_CONSTANT(half_pi, 1.570796326794896619231321691639751442e+00, "1.57079632679489661923132169163975144209858469968755291048747229615390820314310449931401741267105853399107404326e+00"); 151</pre> 152<p> 153 This macro BOOST_DEFINE_MATH_CONSTANT inserts a C++ struct code snippet that 154 declares the <code class="computeroutput"><span class="keyword">float</span></code>, <code class="computeroutput"><span class="keyword">double</span></code> and <code class="computeroutput"><span class="keyword">long</span> 155 <span class="keyword">double</span></code> versions of the constant, plus 156 a decimal digit string representation correct to 100 decimal digits, and all 157 the meta-programming machinery needed to select between them. 158 </p> 159<p> 160 The result of an expanded macro for Pi is shown below. 161 </p> 162<pre class="programlisting"><span class="comment">// Preprocessed pi constant, annotated.</span> 163 164<span class="keyword">namespace</span> <span class="identifier">boost</span> 165<span class="special">{</span> 166 <span class="keyword">namespace</span> <span class="identifier">math</span> 167 <span class="special">{</span> 168 <span class="keyword">namespace</span> <span class="identifier">constants</span> 169 <span class="special">{</span> 170 <span class="keyword">namespace</span> <span class="identifier">detail</span> 171 <span class="special">{</span> 172 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">constant_pi</span> 173 <span class="special">{</span> 174 <span class="keyword">private</span><span class="special">:</span> 175 <span class="comment">// Default implementations from string of decimal digits:</span> 176 <span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get_from_string</span><span class="special">()</span> 177 <span class="special">{</span> 178 <span class="keyword">static</span> <span class="keyword">const</span> <span class="identifier">T</span> <span class="identifier">result</span> 179 <span class="special">=</span> <span class="identifier">detail</span><span class="special">::</span><span class="identifier">convert_from_string</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="string">"3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651e+00"</span><span class="special">,</span> 180 <span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_convertible</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*,</span> <span class="identifier">T</span><span class="special">>());</span> 181 <span class="keyword">return</span> <span class="identifier">result</span><span class="special">;</span> 182 <span class="special">}</span> 183 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">></span> <span class="keyword">static</span> <span class="identifier">T</span> <span class="identifier">compute</span><span class="special">();</span> 184 185 <span class="keyword">public</span><span class="special">:</span> 186 <span class="comment">// Default implementations from string of decimal digits:</span> 187 <span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">construct_from_string</span><span class="special">>&)</span> 188 <span class="special">{</span> 189 <span class="identifier">constant_initializer</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="special">&</span> <span class="identifier">constant_pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get_from_string</span> <span class="special">>::</span><span class="identifier">do_nothing</span><span class="special">();</span> 190 <span class="keyword">return</span> <span class="identifier">get_from_string</span><span class="special">();</span> 191 <span class="special">}</span> 192 <span class="comment">// Float, double and long double versions:</span> 193 <span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">construct_from_float</span><span class="special">>)</span> 194 <span class="special">{</span> 195 <span class="keyword">return</span> <span class="number">3.141592653589793238462643383279502884e+00F</span><span class="special">;</span> 196 <span class="special">}</span> 197 <span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">construct_from_double</span><span class="special">>&)</span> 198 <span class="special">{</span> 199 <span class="keyword">return</span> <span class="number">3.141592653589793238462643383279502884e+00</span><span class="special">;</span> 200 <span class="special">}</span> 201 <span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">construct_from_long_double</span><span class="special">>&)</span> 202 <span class="special">{</span> 203 <span class="keyword">return</span> <span class="number">3.141592653589793238462643383279502884e+00L</span><span class="special">;</span> 204 <span class="special">}</span> 205 <span class="comment">// For very high precision that is nonetheless can be calculated at compile time:</span> 206 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">int</span> <span class="identifier">N</span><span class="special">></span> <span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">N</span><span class="special">>&</span> <span class="identifier">n</span><span class="special">)</span> 207 <span class="special">{</span> 208 <span class="identifier">constant_initializer2</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">N</span><span class="special">,</span> <span class="special">&</span> <span class="identifier">constant_pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">template</span> <span class="identifier">compute</span><span class="special"><</span><span class="identifier">N</span><span class="special">></span> <span class="special">>::</span><span class="identifier">do_nothing</span><span class="special">();</span> 209 <span class="keyword">return</span> <span class="identifier">compute</span><span class="special"><</span><span class="identifier">N</span><span class="special">>();</span> 210 <span class="special">}</span> 211 <span class="comment">//For true arbitrary precision, which may well vary at runtime.</span> 212 <span class="keyword">static</span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="number">0</span><span class="special">>&)</span> 213 <span class="special">{</span> 214 <span class="keyword">return</span> <span class="identifier">tools</span><span class="special">::</span><span class="identifier">digits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>()</span> <span class="special">></span> <span class="identifier">max_string_digits</span> <span class="special">?</span> <span class="identifier">compute</span><span class="special"><</span><span class="number">0</span><span class="special">>()</span> <span class="special">:</span> <span class="identifier">get</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">integral_constant</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">construct_from_string</span><span class="special">>());</span> 215 <span class="special">}</span> 216 <span class="special">};</span> <span class="comment">// template <class T> struct constant_pi</span> 217 <span class="special">}</span> <span class="comment">// namespace detail</span> 218 219 <span class="comment">// The actual forwarding function (including policy to control precision).</span> 220 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">Policy</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">pi</span><span class="special">(</span> <span class="special">)</span> 221 <span class="special">{</span> 222 <span class="keyword">return</span> <span class="identifier">detail</span><span class="special">::</span> <span class="identifier">constant_pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get</span><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">construction_traits</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Policy</span><span class="special">>::</span><span class="identifier">type</span><span class="special">());</span> 223 <span class="special">}</span> 224 <span class="comment">// The actual forwarding function (using default policy to control precision).</span> 225 <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="identifier">pi</span><span class="special">()</span> 226 <span class="special">{</span> 227 <span class="keyword">return</span> <span class="identifier">pi</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">::</span><span class="identifier">policy</span><span class="special"><></span> <span class="special">>()</span> 228 <span class="special">}</span> 229 <span class="special">}</span> <span class="comment">// namespace constants</span> 230 231 <span class="comment">// Namespace specific versions, for the three built-in floats:</span> 232 <span class="keyword">namespace</span> <span class="identifier">float_constants</span> 233 <span class="special">{</span> 234 <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">float</span> <span class="identifier">pi</span> <span class="special">=</span> <span class="number">3.141592653589793238462643383279502884e+00F</span><span class="special">;</span> 235 <span class="special">}</span> 236 <span class="keyword">namespace</span> <span class="identifier">double_constants</span> 237 <span class="special">{</span> 238 <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">double</span> <span class="identifier">pi</span> <span class="special">=</span> <span class="number">3.141592653589793238462643383279502884e+00</span><span class="special">;</span> 239 <span class="special">}</span> 240 <span class="keyword">namespace</span> <span class="identifier">long_double_constants</span> 241 <span class="special">{</span> 242 <span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">long</span> <span class="keyword">double</span> <span class="identifier">pi</span> <span class="special">=</span> <span class="number">3.141592653589793238462643383279502884e+00L</span><span class="special">;</span> 243 <span class="special">}</span> 244 <span class="keyword">namespace</span> <span class="identifier">constants</span><span class="special">{;</span> 245 <span class="special">}</span> <span class="comment">// namespace constants</span> 246 <span class="special">}</span> <span class="comment">// namespace math</span> 247<span class="special">}</span> <span class="comment">// namespace boost</span> 248</pre> 249</div> 250<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 251<td align="left"></td> 252<td align="right"><div class="copyright-footer">Copyright © 2006-2019 Nikhar 253 Agrawal, Anton Bikineev, Paul A. Bristow, Marco Guazzone, Christopher Kormanyos, 254 Hubert Holin, Bruno Lalande, John Maddock, Jeremy Murphy, Matthew Pulver, Johan 255 Råde, Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg, 256 Daryle Walker and Xiaogang Zhang<p> 257 Distributed under the Boost Software License, Version 1.0. (See accompanying 258 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>) 259 </p> 260</div></td> 261</tr></table> 262<hr> 263<div class="spirit-nav"> 264<a accesskey="p" href="constants.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../constants.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="constants_faq.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 265</div> 266</body> 267</html> 268
