1 // Boost.Units - A C++ library for zero-overhead dimensional analysis and
2 // unit/quantity manipulation and conversion
3 //
4 // Copyright (C) 2003-2008 Matthias Christian Schabel
5 // Copyright (C) 2008 Steven Watanabe
6 //
7 // Distributed under the Boost Software License, Version 1.0. (See
8 // accompanying file LICENSE_1_0.txt or copy at
9 // http://www.boost.org/LICENSE_1_0.txt)
10
11 #include <boost/units/base_dimension.hpp>
12 #include <boost/units/base_unit.hpp>
13 #include <boost/units/unit.hpp>
14 #include <boost/units/quantity.hpp>
15
16 //[runtime_conversion_factor_snippet_1
17
18 using boost::units::base_dimension;
19 using boost::units::base_unit;
20
21 static const long currency_base = 1;
22
23 struct currency_base_dimension : base_dimension<currency_base_dimension, 1> {};
24
25 typedef currency_base_dimension::dimension_type currency_type;
26
27 template<long N>
28 struct currency_base_unit :
29 base_unit<currency_base_unit<N>, currency_type, currency_base + N> {};
30
31 typedef currency_base_unit<0> us_dollar_base_unit;
32 typedef currency_base_unit<1> euro_base_unit;
33
34 typedef us_dollar_base_unit::unit_type us_dollar;
35 typedef euro_base_unit::unit_type euro;
36
37 // an array of all possible conversions
38 double conversion_factors[2][2] = {
39 {1.0, 1.0},
40 {1.0, 1.0}
41 };
42
get_conversion_factor(long from,long to)43 double get_conversion_factor(long from, long to) {
44 return(conversion_factors[from][to]);
45 }
46
set_conversion_factor(long from,long to,double value)47 void set_conversion_factor(long from, long to, double value) {
48 conversion_factors[from][to] = value;
49 conversion_factors[to][from] = 1.0 / value;
50 }
51
52 BOOST_UNITS_DEFINE_CONVERSION_FACTOR_TEMPLATE((long N1)(long N2),
53 currency_base_unit<N1>,
54 currency_base_unit<N2>,
55 double, get_conversion_factor(N1, N2));
56
57 //]
58
main()59 int main() {
60 boost::units::quantity<us_dollar> dollars = 2.00 * us_dollar();
61 boost::units::quantity<euro> euros(dollars);
62 set_conversion_factor(0, 1, 2.0);
63 dollars = static_cast<boost::units::quantity<us_dollar> >(euros);
64 set_conversion_factor(0, 1, .5);
65 euros = static_cast<boost::units::quantity<euro> >(dollars);
66 double value = euros.value(); // = .5
67 if(value != .5) {
68 return(1);
69 } else {
70 return(0);
71 }
72 }
73