std::throw_with_nested (3) - Linux Manuals

std::throw_with_nested: std::throw_with_nested

NAME

std::throw_with_nested - std::throw_with_nested

Synopsis

Defined in header <exception>
template< class T > (since C++11)
[[noreturn]] void throw_with_nested( T&& t );

If std::decay<T>::type is a non-final non-union class type that is neither std::nested_exception nor derived from std::nested_exception, throws an exception of an unspecified type that is publicly derived from both std::nested_exception and from std::decay<T>::type, and constructed from std::forward<T>(t). The default constructor of the nested_exception base class calls std::current_exception, capturing the currently handled exception object, if any, in a std::exception_ptr.
Otherwise, throws std::forward<T>(t).
Requires that std::decay<T>::type is CopyConstructible

Parameters

t - the exception object to throw

Return value

(none)

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& e) {
          print_exception(e, 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);
      }
  }

Output:

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