154 lines
4.2 KiB
C++
154 lines
4.2 KiB
C++
// example_error_handling.cpp
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// Copyright Paul A. Bristow 2007, 2010.
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// Copyright John Maddock 2007.
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// Use, modification and distribution are subject to the
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// Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt
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// or copy at http://www.boost.org/LICENSE_1_0.txt)
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// Note that this file contains quickbook markup as well as code
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// and comments, don't change any of the special comment markups!
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// Optional macro definitions described in text below:
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// #define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
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// #define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
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// #define BOOST_MATH_DOMAIN_ERROR_POLICY is set to: throw_on_error
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//[error_handling_example
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/*`
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The following example demonstrates the effect of
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setting the macro BOOST_MATH_DOMAIN_ERROR_POLICY
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when an invalid argument is encountered. For the
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purposes of this example, we'll pass a negative
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degrees of freedom parameter to the student's t
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distribution.
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Since we know that this is a single file program we could
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just add:
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#define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
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to the top of the source file to change the default policy
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to one that simply returns a NaN when a domain error occurs.
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Alternatively we could use:
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#define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
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To ensure the `::errno` is set when a domain error occurs
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as well as returning a NaN.
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This is safe provided the program consists of a single
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translation unit /and/ we place the define /before/ any
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#includes. Note that should we add the define after the includes
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then it will have no effect! A warning such as:
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[pre warning C4005: 'BOOST_MATH_OVERFLOW_ERROR_POLICY' : macro redefinition]
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is a certain sign that it will /not/ have the desired effect.
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We'll begin our sample program with the needed includes:
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*/
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#define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
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// Boost
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#include <boost/math/distributions/students_t.hpp>
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using boost::math::students_t; // Probability of students_t(df, t).
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// std
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#include <iostream>
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using std::cout;
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using std::endl;
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#include <stdexcept>
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#include <cstddef>
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// using ::errno
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/*`
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Next we'll define the program's main() to call the student's t
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distribution with an invalid degrees of freedom parameter,
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the program is set up to handle either an exception or a NaN:
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*/
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int main()
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{
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cout << "Example error handling using Student's t function. " << endl;
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cout << "BOOST_MATH_DOMAIN_ERROR_POLICY is set to: "
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<< BOOST_STRINGIZE(BOOST_MATH_DOMAIN_ERROR_POLICY) << endl;
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double degrees_of_freedom = -1; // A bad argument!
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double t = 10;
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try
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{
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errno = 0; // Clear/reset.
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students_t dist(degrees_of_freedom); // exception is thrown here if enabled.
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double p = cdf(dist, t);
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// Test for error reported by other means:
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if((boost::math::isnan)(p))
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{
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cout << "cdf returned a NaN!" << endl;
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if (errno != 0)
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{ // So errno has been set.
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cout << "errno is set to: " << errno << endl;
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}
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}
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else
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cout << "Probability of Student's t is " << p << endl;
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}
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catch(const std::exception& e)
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{
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std::cout <<
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"\n""Message from thrown exception was:\n " << e.what() << std::endl;
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}
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return 0;
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} // int main()
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/*`
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Here's what the program output looks like with a default build
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(one that *does throw exceptions*):
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[pre
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Example error handling using Student's t function.
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BOOST_MATH_DOMAIN_ERROR_POLICY is set to: throw_on_error
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Message from thrown exception was:
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Error in function boost::math::students_t_distribution<double>::students_t_distribution:
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Degrees of freedom argument is -1, but must be > 0 !
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]
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Alternatively let's build with:
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#define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
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Now the program output is:
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[pre
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Example error handling using Student's t function.
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BOOST_MATH_DOMAIN_ERROR_POLICY is set to: ignore_error
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cdf returned a NaN!
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]
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And finally let's build with:
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#define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
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Which gives the output show errno:
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[pre
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Example error handling using Student's t function.
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BOOST_MATH_DOMAIN_ERROR_POLICY is set to: errno_on_error
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cdf returned a NaN!
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errno is set to: 33
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]
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*/
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//] [error_handling_eg end quickbook markup]
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