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std::rethrow_if_nested

From cppreference.com
< cpp‎ | error
 
C++
 
Diagnostics library
 
Defined in header <exception>
template< class E >
void rethrow_if_nested( const E& e );
 (since C++11)
(constexpr since C++26)

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

[edit]

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 <<