std::throw_with_nested
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Diagnostics library
(until C++20*)
(C++17)(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
throw_with_nested
(C++11)
(C++11)
Exception handling failures
(C++11)
(until C++17*)
(until C++17*)
(until C++17*)
(until C++17*)
(TM TS)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++23)
(C++23)
(C++26)
(C++26)
(C++26)
Defined in header
<exception>
template< class T >
[[noreturn]] void throw_with_nested( T&& t );
(since C++11) [[noreturn]] void throw_with_nested( T&& t );
(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.
Contents
[edit] Parameters
t
-
the exception object to throw
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_constexpr_exceptions |
202411L |
(C++26) | constexpr for exception types |
[edit] 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