ceph/src/boost/libs/math/example/error_handling_example.cpp

   1 // example_error_handling.cpp
   2
   3 // Copyright Paul A. Bristow 2007, 2010.
   4 // Copyright John Maddock 2007.
   5
   6 // Use, modification and distribution are subject to the
   7 // Boost Software License, Version 1.0.
   8 // (See accompanying file LICENSE_1_0.txt
   9 // or copy at http://www.boost.org/LICENSE_1_0.txt)
  10
  11 // Note that this file contains quickbook markup as well as code
  12 // and comments, don't change any of the special comment markups!
  13
  14 // Optional macro definitions described in text below:
  15 //   #define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
  16 //   #define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
  17 //   #define BOOST_MATH_DOMAIN_ERROR_POLICY is set to: throw_on_error
  18
  19 //[error_handling_example
  20 /*`
  21 The following example demonstrates the effect of
  22 setting the macro BOOST_MATH_DOMAIN_ERROR_POLICY
  23 when an invalid argument is encountered.  For the
  24 purposes of this example, we'll pass a negative
  25 degrees of freedom parameter to the student's t
  26 distribution.
  27
  28 Since we know that this is a single file program we could
  29 just add:
  30
  31    #define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
  32
  33 to the top of the source file to change the default policy
  34 to one that simply returns a NaN when a domain error occurs.
  35 Alternatively we could use:
  36
  37    #define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
  38
  39 To ensure the `::errno` is set when a domain error occurs
  40 as well as returning a NaN.
  41
  42 This is safe provided the program consists of a single
  43 translation unit /and/ we place the define /before/ any
  44 #includes.  Note that should we add the define after the includes
  45 then it will have no effect!  A warning such as:
  46
  47 [pre warning C4005: 'BOOST_MATH_OVERFLOW_ERROR_POLICY' : macro redefinition]
  48
  49 is a certain sign that it will /not/ have the desired effect.
  50
  51 We'll begin our sample program with the needed includes:
  52 */
  53
  54
  55    #define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
  56
  57 // Boost
  58 #include <boost/math/distributions/students_t.hpp>
  59    using boost::math::students_t;  // Probability of students_t(df, t).
  60
  61 // std
  62 #include <iostream>
  63    using std::cout;
  64    using std::endl;
  65
  66 #include <stdexcept>
  67
  68
  69 #include <cstddef>
  70    // using ::errno
  71
  72 /*`
  73 Next we'll define the program's main() to call the student's t
  74 distribution with an invalid degrees of freedom parameter,
  75 the program is set up to handle either an exception or a NaN:
  76 */
  77
  78 int main()
  79 {
  80    cout << "Example error handling using Student's t function. " << endl;
  81    cout << "BOOST_MATH_DOMAIN_ERROR_POLICY is set to: "
  82       << BOOST_STRINGIZE(BOOST_MATH_DOMAIN_ERROR_POLICY) << endl;
  83
  84    double degrees_of_freedom = -1; // A bad argument!
  85    double t = 10;
  86
  87    try
  88    {
  89       errno = 0; // Clear/reset.
  90       students_t dist(degrees_of_freedom); // exception is thrown here if enabled.
  91       double p = cdf(dist, t);
  92       // Test for error reported by other means:
  93       if((boost::math::isnan)(p))
  94       {
  95          cout << "cdf returned a NaN!" << endl;
  96          if (errno != 0)
  97          { // So errno has been set.
  98            cout << "errno is set to: " << errno << endl;
  99          }
 100       }
 101       else
 102          cout << "Probability of Student's t is " << p << endl;
 103    }
 104    catch(const std::exception& e)
 105    {
 106       std::cout <<
 107          "\n""Message from thrown exception was:\n   " << e.what() << std::endl;
 108    }
 109    return 0;
 110 } // int main()
 111
 112 /*`
 113
 114 Here's what the program output looks like with a default build
 115 (one that *does throw exceptions*):
 116
 117 [pre
 118 Example error handling using Student's t function.
 119 BOOST_MATH_DOMAIN_ERROR_POLICY is set to: throw_on_error
 120
 121 Message from thrown exception was:
 122    Error in function boost::math::students_t_distribution<double>::students_t_distribution:
 123    Degrees of freedom argument is -1, but must be > 0 !
 124 ]
 125
 126 Alternatively let's build with:
 127
 128    #define BOOST_MATH_DOMAIN_ERROR_POLICY ignore_error
 129
 130 Now the program output is:
 131
 132 [pre
 133 Example error handling using Student's t function.
 134 BOOST_MATH_DOMAIN_ERROR_POLICY is set to: ignore_error
 135 cdf returned a NaN!
 136 ]
 137
 138 And finally let's build with:
 139
 140    #define BOOST_MATH_DOMAIN_ERROR_POLICY errno_on_error
 141
 142 Which gives the output show errno:
 143
 144 [pre
 145 Example error handling using Student's t function.
 146 BOOST_MATH_DOMAIN_ERROR_POLICY is set to: errno_on_error
 147 cdf returned a NaN!
 148 errno is set to: 33
 149 ]
 150
 151 */
 152
 153 //] [error_handling_eg end quickbook markup]