std::throw_with_nested
From cppreference.com
| Defined in header <exception>
|
||
template< class T > [[noreturn]] void throw_with_nested( T&& t ); |
(since C++11) (constexpr since C++26) |
|
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 |
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_constexpr_exceptions |
202411L |
(C++26) | constexpr for exception types
|
Example
Demonstrates construction and recursion through a nested exception object.
Run this code
#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);
}
}
Possible output:
exception: run() failed
exception: Couldn't open nonexistent.file
exception: basic_ios::clear
See also
(C++11) |
a mixin type to capture and store current exceptions (class) |
(C++11) |
throws the exception from a std::nested_exception (function template) |