108 lines
2.8 KiB
C++
108 lines
2.8 KiB
C++
// Copyright John Maddock 2007.
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// Copyright Paul A. Bristow 2010
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// Use, modification and distribution are subject to the
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// Boost Software License, Version 1.0. (See accompanying file
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// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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// Note that this file contains quickbook mark-up as well as code
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// and comments, don't change any of the special comment mark-ups!
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#include <iostream>
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using std::cout; using std::endl;
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#include <cerrno> // for ::errno
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//[policy_eg_4
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/*`
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Suppose we want `C::foo()` to behave in a C-compatible way and set
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`::errno` on error rather than throwing any exceptions.
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We'll begin by including the needed header for our function:
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*/
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#include <boost/math/special_functions.hpp>
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//using boost::math::tgamma; // Not needed because using C::tgamma.
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/*`
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Open up the "C" namespace that we'll use for our functions, and
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define the policy type we want: in this case a C-style one that sets
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::errno and returns a standard value, rather than throwing exceptions.
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Any policies we don't specify here will inherit the defaults.
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*/
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namespace C
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{ // To hold our C-style policy.
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//using namespace boost::math::policies; or explicitly:
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using boost::math::policies::policy;
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using boost::math::policies::domain_error;
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using boost::math::policies::pole_error;
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using boost::math::policies::overflow_error;
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using boost::math::policies::evaluation_error;
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using boost::math::policies::errno_on_error;
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typedef policy<
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domain_error<errno_on_error>,
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pole_error<errno_on_error>,
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overflow_error<errno_on_error>,
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evaluation_error<errno_on_error>
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> c_policy;
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/*`
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All we need do now is invoke the BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS
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macro passing our policy type c_policy as the single argument:
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*/
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BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS(c_policy)
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} // close namespace C
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/*`
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We now have a set of forwarding functions defined in namespace C
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that all look something like this:
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``
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template <class RealType>
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inline typename boost::math::tools::promote_args<RT>::type
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tgamma(RT z)
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{
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return boost::math::tgamma(z, c_policy());
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}
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``
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So that when we call `C::tgamma(z)`, we really end up calling
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`boost::math::tgamma(z, C::c_policy())`:
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*/
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int main()
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{
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errno = 0;
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cout << "Result of tgamma(30000) is: "
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<< C::tgamma(30000) << endl; // Note using C::tgamma
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cout << "errno = " << errno << endl; // errno = 34
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cout << "Result of tgamma(-10) is: "
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<< C::tgamma(-10) << endl;
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cout << "errno = " << errno << endl; // errno = 33, overwriting previous value of 34.
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}
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/*`
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Which outputs:
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[pre
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Result of C::tgamma(30000) is: 1.#INF
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errno = 34
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Result of C::tgamma(-10) is: 1.#QNAN
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errno = 33
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]
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This mechanism is particularly useful when we want to define a project-wide policy,
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and don't want to modify the Boost source,
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or to set project wide build macros (possibly fragile and easy to forget).
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*/
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//] //[/policy_eg_4]
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