17 Language support library [support]

17.9 Exception handling [support.exception]

17.9.8 nested_exception [except.nested]

namespace std { class nested_exception { public: nested_exception() noexcept; nested_exception(const nested_exception&) noexcept = default; nested_exception& operator=(const nested_exception&) noexcept = default; virtual ~nested_exception() = default; // access functions [[noreturn]] void rethrow_nested() const; exception_ptr nested_ptr() const noexcept; }; template<class T> [[noreturn]] void throw_with_nested(T&& t); template<class E> void rethrow_if_nested(const E& e); }
The class nested_exception is designed for use as a mixin through multiple inheritance.
It captures the currently handled exception and stores it for later use.
[Note 1: 
nested_exception has a virtual destructor to make it a polymorphic class.
Its presence can be tested for with dynamic_cast.
— end note]
nested_exception() noexcept;
Effects: The constructor calls current_exception() and stores the returned value.
[[noreturn]] void rethrow_nested() const;
Effects: If nested_ptr() returns a null pointer, the function calls the function std​::​terminate.
Otherwise, it throws the stored exception captured by *this.
exception_ptr nested_ptr() const noexcept;
Returns: The stored exception captured by this nested_exception object.
template<class T> [[noreturn]] void throw_with_nested(T&& t);
Let U be decay_t<T>.
Preconditions: U meets the Cpp17CopyConstructible requirements.
Throws: If is_class_v<U> && !is_final_v<U> && !is_base_of_v<nested_exception, U> is true, an exception of unspecified type that is publicly derived from both U and nested_exception and constructed from std​::​forward<T>(t), otherwise std​::​forward<T>(t).
template<class E> void rethrow_if_nested(const E& e);
Effects: If E is not a polymorphic class type, or if nested_exception is an inaccessible or ambiguous base class of E, there is no effect.
Otherwise, performs: if (auto p = dynamic_cast<const nested_exception*>(addressof(e))) p->rethrow_nested();