std::throw_with_nested (3) Linux Manual Page

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

See also

nested_exception a mixin type to capture and store current exceptions
                  (class)
(C++11)
rethrow_if_nested throws the exception from a std::nested_exception
                  (function template)
(C++11)