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std::exception_ptr(3)	      C++ Standard Libary	 std::exception_ptr(3)

NAME
       std::exception_ptr - std::exception_ptr

Synopsis
	  Defined in header <exception>
	  typedef /*unspecified*/ exception_ptr;  (since C++11)

	  std::exception_ptr  is  a nullable pointer-like type that manages an
       exception object
	  which	has been thrown	and captured with  std::current_exception.  An
       instance	of
	  std::exception_ptr  may  be  passed to another function, possibly on
       another thread,
	  where	the exception may be rethrown and handled with a catch clause.

	  A default-constructed	std::exception_ptr is a	null pointer; it  does
       not point to an
	  exception object.

	  Two  instances  of std::exception_ptr	compare	equal only if they are
       both null or both
	  point	at the same exception object.

	  std::exception_ptr is	not implicitly convertible to any  arithmetic,
       enumeration, or
	  pointer type.	It is contextually convertible to bool,	and will eval-
       uate to false if
	  it is	null, true otherwise.

	  The  exception  object  referenced  by an std::exception_ptr remains
       valid as	long as
	  there	remains	at least one std::exception_ptr	 that  is  referencing
       it:
	  std::exception_ptr  is  a shared-ownership smart pointer (note: this
       is in addition to
	  the usual exception object lifetime rules).

	  std::exception_ptr meets the requirements of NullablePointer.

Example
       // Run this code

	#include <exception>
	#include <iostream>
	#include <stdexcept>
	#include <string>

	void handle_eptr(std::exception_ptr eptr) // passing by	value is ok
	{
	    try
	    {
		if (eptr)
		    std::rethrow_exception(eptr);
	    }
	    catch(const	std::exception&	e)
	    {
		std::cout << "Caught exception:	'" << e.what() << "'\n";
	    }
	}

	int main()
	{
	    std::exception_ptr eptr;

	    try
	    {
		std::string().at(1); //	this generates a std::out_of_range
	    }
	    catch(...)
	    {
		eptr = std::current_exception(); // capture
	    }

	    handle_eptr(eptr);

	} // destructor	for std::out_of_range called here, when	 the  eptr  is
       destructed

Possible output:
	Caught	exception: 'basic_string::at: __n (which is 1) >= this->size()
       (which is 0)'

See also
	  make_exception_ptr creates an	std::exception_ptr from	 an  exception
       object
	  (C++11)	     (function template)
	  current_exception   captures	the current exception in a std::excep-
       tion_ptr
	  (C++11)	     (function)
	  rethrow_exception  throws the	exception from an std::exception_ptr
	  (C++11)	     (function)

http://cppreference.com		  2024.06.10		 std::exception_ptr(3)

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