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