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  1. // ____________________________________[ uncaught_exception_count.hpp ]____________________________________
  2. //             Copyright Evgeny Panasyuk 2012.
  3. // Distributed under the Boost Software License, Version 1.0.
  4. //    (See accompanying file LICENSE_1_0.txt or copy at
  5. //          http://w...content-available-to-author-only...t.org/LICENSE_1_0.txt)
  6.  
  7. // e-mail: E?????[dot]P???????[at]gmail.???
  8.  
  9. #ifndef BOOST_UNCAUGHT_EXCEPTION_COUNT_HPP_39A1E90FC11647e08D5F6ED16CD34B34
  10. #define BOOST_UNCAUGHT_EXCEPTION_COUNT_HPP_39A1E90FC11647e08D5F6ED16CD34B34
  11.  
  12. #if defined(_MSC_VER) || defined(__GNUG__) || defined(__CLANG__)
  13.     #define BOOST_UNCAUGHT_EXCEPTION_COUNT_SUPPORTED 1
  14. #endif
  15.  
  16. namespace boost
  17. {
  18.     namespace exception_detail
  19.     {
  20.         template<typename To> inline
  21.         To *unrelated_pointer_cast(void *from)
  22.         {
  23.             return static_cast<To*>(from);
  24.         }
  25.     }
  26.  
  27.     // uncaught_exception_count is a function similar to std::uncaught_exception from standard library,
  28.     // but instead of boolean result it returns unsigned int showing current count of uncaught exceptions.
  29.  
  30. #if defined(_MSC_VER)
  31.     namespace exception_detail
  32.     {
  33.         extern "C" char * __cdecl _getptd();
  34.     }
  35.     inline unsigned uncaught_exception_count()
  36.     {
  37.         // MSVC specific. Tested on {MSVC2005SP1,MSVC2008SP1,MSVC2010SP1,MSVC2012}x{x32,x64}.
  38.         return *exception_detail::unrelated_pointer_cast<unsigned>
  39.         (
  40.             exception_detail::_getptd() + (sizeof(void*)==8 ? 0x100 : 0x90) 
  41.         );
  42.     }
  43. #elif defined(__GNUG__) || defined(__CLANG__)
  44.     namespace exception_detail
  45.     {
  46.         extern "C" char * __cxa_get_globals();
  47.     }
  48.     inline unsigned uncaught_exception_count()
  49.     {
  50.         // Tested on {Clang 3.2,GCC 3.4.6,GCC 4.1.2,GCC 4.4.6,GCC 4.4.7}x{x32,x64}
  51.         return *exception_detail::unrelated_pointer_cast<unsigned>
  52.         (
  53.             exception_detail::__cxa_get_globals() + (sizeof(void*)==8 ? 0x8 : 0x4)
  54.         );
  55.     }
  56. #endif
  57.  
  58.     // Within one scope uncaught_exception_count can be changed only by +1.
  59.     // uncaught_exception_count_latch is primitive which helps to determine such transition.
  60.     //     Internally it stores and compares only last bit of uncaught_exception_count value
  61. #ifdef BOOST_UNCAUGHT_EXCEPTION_COUNT_SUPPORTED
  62.     class uncaught_exception_count_latch
  63.     {
  64.             unsigned char enter_state;
  65.         public:
  66.             uncaught_exception_count_latch()
  67.                 : enter_state(static_cast<unsigned char>( uncaught_exception_count() & 1 ))
  68.             {
  69.             }
  70.             bool transitioned() const
  71.             {
  72.                 return enter_state != ( uncaught_exception_count() & 1 );
  73.             }
  74.     };
  75. #endif
  76.  
  77. }
  78.  
  79. #endif
  80. // ________________________________________________________________________________________________________
  81.  
  82. #include <type_traits>
  83. #include <iostream>
  84. #include <ostream>
  85. #include <utility>
  86. #include <string>
  87.  
  88. // Proof-of-concept:
  89.  
  90. enum Scope {scope_exit, scope_failure, scope_success};
  91.  
  92. template<Scope scope_type, typename F>
  93. class Guard
  94. {
  95.     boost::uncaught_exception_count_latch latch;
  96.     F f;
  97. public:
  98.     Guard(F &&f)
  99.         : f(std::move(f))
  100.     {}
  101.     ~Guard() noexcept(noexcept(f()))
  102.     {
  103.         if(latch.transitioned() != (scope_type == scope_success))
  104.             f();
  105.     }
  106. };
  107.  
  108. template<typename F>
  109. class Guard<scope_exit, F>
  110. {
  111.     F f;
  112. public:
  113.     Guard(F &&f)
  114.         : f(std::move(f))
  115.     {}
  116.     ~Guard() noexcept(noexcept(f()))
  117.     {
  118.         f();
  119.     }
  120. };
  121.  
  122. // http://c...content-available-to-author-only...n.com/Shows/Going+Deep/C-and-Beyond-2012-Andrei-Alexandrescu-Systematic-Error-Handling-in-C
  123. template<Scope scope_type>
  124. struct Aux
  125. {
  126.     template<typename F>
  127.         Guard<scope_type, typename std::decay<F>::type>
  128.     operator*(F &&f) const
  129.     {
  130.         return Guard<scope_type, typename std::decay<F>::type>( std::forward<F>(f) );
  131.     }
  132. };
  133.  
  134. #define CONCAT(x, y) CONCAT2(x, y)
  135. #define CONCAT2(x, y) x ## y
  136.  
  137. #define scope(scope_type) auto CONCAT(aux, __LINE__)= Aux<scope_##scope_type>()*[&]
  138.  
  139. int main()
  140. {
  141.     using namespace std;
  142.     {
  143.         cout << "success case:" << endl;
  144.         scope(exit)
  145.         {
  146.             cout << "exit" << endl;
  147.         };
  148.         scope(success)
  149.         {
  150.             cout << "success" << endl;
  151.         };
  152.         scope(failure)
  153.         {
  154.             cout << "failure" << endl;
  155.         };
  156.     }
  157.     cout << string(16,'_') << endl;
  158.     try
  159.     {
  160.         cout << "failure case:" << endl;
  161.         scope(exit)
  162.         {
  163.             cout << "exit" << endl;
  164.         };
  165.         scope(success)
  166.         {
  167.             cout << "success" << endl;
  168.         };
  169.         scope(failure)
  170.         {
  171.             cout << "failure" << endl;
  172.         };
  173.         throw 1;
  174.     }
  175.     catch(int){}
  176. }
  177.  
Success #stdin #stdout 0s 3432KB
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Standard input is empty
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success case:
success
exit
________________
failure case:
failure
exit
https://ideone.com/O8zEiX
scope(exit/success/failure)
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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