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// 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.
*/
//]
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