std::rethrow_if_nested
From cppreference.com
Defined in header <exception>
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template< class E > void rethrow_if_nested( const E& e ); |
(since C++11) (constexpr since C++26) |
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If E
is not a polymorphic class type, or if std::nested_exception is an inaccessible or ambiguous base class of E
, there is no effect.
Otherwise, performs
if (auto p = dynamic_cast<const std::nested_exception*>(std::addressof(e))) p->rethrow_nested();
Contents |
[edit] Parameters
e | - | the exception object to rethrow |
[edit] Notes
Unlike many related functions, this function is not intended to be called with a std::exception_ptr but rather an actual exception reference.
Feature-test macro | Value | Std | Feature |
---|---|---|---|
__cpp_lib_constexpr_exceptions |
202411L |
(C++26) | constexpr for exception types |
[edit] Possible implementation
namespace details { template<class E> struct can_dynamic_cast : std::integral_constant<bool, std::is_polymorphic<E>::value && (!std::is_base_of<std::nested_exception, E>::value || std::is_convertible<E*, std::nested_exception*>::value) > {}; template<class T> void rethrow_if_nested_impl(const T& e, std::true_type) { if (auto nep = dynamic_cast<const std::nested_exception*>(std::addressof(e))) nep->rethrow_nested(); } template<class T> void rethrow_if_nested_impl(const T&, std::false_type) {} } template<class T> void rethrow_if_nested(const T& t) { details::rethrow_if_nested_impl(t, details::can_dynamic_cast<T>()); } |
[edit] Example
Demonstrates construction and recursion through a nested exception object.
Run this code
#include <exception> #include <fstream> #include <iostream> #include <stdexcept> #include <string> // prints the explanatory string of an exception. If the exception is nested, // recurses to print the explanatory string of the exception it holds void print_exception(const std::exception& e, int level = 0) { std::cerr << std::string(level, ' ') << "exception: " << e.what() << '\n'; try { std::rethrow_if_nested(e); } catch (const std::exception& nestedException) { print_exception(nestedException, level + 1); } catch (...) {} } // sample function that catches an exception and wraps it in a nested exception void open_file(const std::string& s) { try { std::ifstream file(s); file.exceptions(std::ios_base::failbit); } catch (...) { std::throw_with_nested(std::runtime_error("Couldn't open " + s)); } } // sample function that catches an exception and wraps it in a nested exception void run() { try { open_file("nonexistent.file"); } catch (...) { std::throw_with_nested(std::runtime_error("run() failed")); } } // runs the sample function above and prints the caught exception int main() { try { run(); } catch (const std::exception& e) { print_exception(e); } }
Possible output:
exception: run() failed exception: Couldn't open nonexistent.file exception: basic_ios::clear
[edit] See also
(C++11) |
a mixin type to capture and store current exceptions (class) |
(C++11) |
throws its argument with std::nested_exception mixed in (function template) |