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