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

NAME
       std::nested_exception - std::nested_exception

Synopsis
	  Defined in header <exception>
	  class	nested_exception;	 (since	C++11)

	  std::nested_exception	is a polymorphic mixin class which can capture
       and store the
	  current  exception,  making  it possible to nest exceptions of arbi-
       trary types within
	  each other.

Member functions
	  constructor	 constructs a nested_exception
			 (public member	function)
	  destructor	 destructs a nested exception
	  [virtual]	 (virtual public member	function)
	  operator=	 replaces the contents of a nested_exception
			 (public member	function)
	  rethrow_nested throws	the stored exception
			 (public member	function)
	  nested_ptr	 obtains a pointer to the stored exception
			 (public member	function)

Non-member functions
	  throw_with_nested throws  its	 argument  with	 std::nested_exception
       mixed in
	  (C++11)	    (function template)
	  rethrow_if_nested throws the exception from a	std::nested_exception
	  (C++11)	    (function template)

Example
	  Demonstrates	construction  and recursion through a nested exception
       object.

       // Run this code

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

	// prints the explanatory string of an exception. If the exception  is
       nested,
	// recurses to print the explanatory 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

See also
	  exception_ptr	    shared pointer type	for handling exception objects
	  (C++11)	    (typedef)
	  throw_with_nested  throws  its  argument  with std::nested_exception
       mixed in
	  (C++11)	    (function template)
	  rethrow_if_nested throws the exception from a	std::nested_exception
	  (C++11)	    (function template)

http://cppreference.com		  2022.07.31	      std::nested_exception(3)

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