std::nested_exception

#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 << 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);
 }
}

exception: run() failed
 exception: Couldn't open nonexistent.file
 exception: basic_ios::clear