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Defined in header <exception> | ||
template<class E> void rethrow_if_nested(const E& e); | (since C++11) (constexpr since C++26) | |
IfE is not a polymorphic class type, or ifstd::nested_exception is an inaccessible or ambiguous base class ofE, there is no effect.
Otherwise, performs
if(auto p=dynamic_cast<conststd::nested_exception*>(std::addressof(e))) p->rethrow_nested();
Contents |
| e | - | the exception object to rethrow |
Unlike many related functions, this function isnot intended to be called with astd::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 |
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<conststd::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>());} |
Demonstrates construction and recursion through a nested exception object.
#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 holdsvoid print_exception(conststd::exception& e,int level=0){std::cerr<<std::string(level,' ')<<"exception: "<< e.what()<<'\n';try{ std::rethrow_if_nested(e);}catch(conststd::exception& nestedException){ print_exception(nestedException, level+1);}catch(...){}} // sample function that catches an exception and wraps it in a nested exceptionvoid open_file(conststd::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 exceptionvoid 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 exceptionint main(){try{ run();}catch(conststd::exception& e){ print_exception(e);}}
Possible output:
exception: run() failed exception: Couldn't open nonexistent.file exception: basic_ios::clear
(C++11) | a mixin type to capture and store current exceptions (class)[edit] |
(C++11) | throws its argument withstd::nested_exception mixed in (function template)[edit] |
