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1 | // Copyright John Maddock 2007. |
2 | // Copyright Paul A. Bristow 2010 | |
3 | ||
4 | // Use, modification and distribution are subject to the | |
5 | // Boost Software License, Version 1.0. (See accompanying file | |
6 | // LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
7 | ||
8 | // Note that this file contains quickbook mark-up as well as code | |
9 | // and comments, don't change any of the special comment mark-ups! | |
10 | ||
11 | #include <iostream> | |
12 | using std::cout; using std::endl; | |
13 | #include <cerrno> // for ::errno | |
14 | ||
15 | //[policy_eg_4 | |
16 | ||
17 | /*` | |
18 | Suppose we want `C::foo()` to behave in a C-compatible way and set | |
19 | `::errno` on error rather than throwing any exceptions. | |
20 | ||
21 | We'll begin by including the needed header for our function: | |
22 | */ | |
23 | ||
24 | #include <boost/math/special_functions.hpp> | |
25 | //using boost::math::tgamma; // Not needed because using C::tgamma. | |
26 | ||
27 | /*` | |
28 | Open up the "C" namespace that we'll use for our functions, and | |
29 | define the policy type we want: in this case a C-style one that sets | |
30 | ::errno and returns a standard value, rather than throwing exceptions. | |
31 | ||
32 | Any policies we don't specify here will inherit the defaults. | |
33 | */ | |
34 | ||
35 | namespace C | |
36 | { // To hold our C-style policy. | |
37 | //using namespace boost::math::policies; or explicitly: | |
38 | using boost::math::policies::policy; | |
39 | ||
40 | using boost::math::policies::domain_error; | |
41 | using boost::math::policies::pole_error; | |
42 | using boost::math::policies::overflow_error; | |
43 | using boost::math::policies::evaluation_error; | |
44 | using boost::math::policies::errno_on_error; | |
45 | ||
46 | typedef policy< | |
47 | domain_error<errno_on_error>, | |
48 | pole_error<errno_on_error>, | |
49 | overflow_error<errno_on_error>, | |
50 | evaluation_error<errno_on_error> | |
51 | > c_policy; | |
52 | ||
53 | /*` | |
54 | All we need do now is invoke the BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS | |
55 | macro passing our policy type c_policy as the single argument: | |
56 | */ | |
57 | ||
58 | BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS(c_policy) | |
59 | ||
60 | } // close namespace C | |
61 | ||
62 | /*` | |
63 | We now have a set of forwarding functions defined in namespace C | |
64 | that all look something like this: | |
65 | ||
66 | `` | |
67 | template <class RealType> | |
68 | inline typename boost::math::tools::promote_args<RT>::type | |
69 | tgamma(RT z) | |
70 | { | |
71 | return boost::math::tgamma(z, c_policy()); | |
72 | } | |
73 | `` | |
74 | ||
75 | So that when we call `C::tgamma(z)`, we really end up calling | |
76 | `boost::math::tgamma(z, C::c_policy())`: | |
77 | */ | |
78 | ||
79 | int main() | |
80 | { | |
81 | errno = 0; | |
82 | cout << "Result of tgamma(30000) is: " | |
83 | << C::tgamma(30000) << endl; // Note using C::tgamma | |
84 | cout << "errno = " << errno << endl; // errno = 34 | |
85 | cout << "Result of tgamma(-10) is: " | |
86 | << C::tgamma(-10) << endl; | |
87 | cout << "errno = " << errno << endl; // errno = 33, overwriting previous value of 34. | |
88 | } | |
89 | ||
90 | /*` | |
91 | ||
92 | Which outputs: | |
93 | ||
94 | [pre | |
95 | Result of C::tgamma(30000) is: 1.#INF | |
96 | errno = 34 | |
97 | Result of C::tgamma(-10) is: 1.#QNAN | |
98 | errno = 33 | |
99 | ] | |
100 | ||
101 | This mechanism is particularly useful when we want to define a project-wide policy, | |
102 | and don't want to modify the Boost source, | |
103 | or to set project wide build macros (possibly fragile and easy to forget). | |
104 | ||
105 | */ | |
106 | //] //[/policy_eg_4] | |
107 |