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.
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 holdsvoid print_exception(conststd::exception& e, int level =0){std::cerr<<std::string(level, ' ')<<"exception: "<< e.what()<<'\n';try{std::rethrow_if_nested(e);}catch(conststd::exception& nestedException){ print_exception(nestedException, level +1);}catch(...){}} // sample function that catches an exception and wraps it in a nested exceptionvoid open_file(conststd::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 exceptionvoid 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 exceptionint main(){try{ run();}catch(conststd::exception& e){ print_exception(e);}}
Possible output:
exception: run() failed exception: Couldn't open nonexistent.file exception: basic_ios::clear
[edit]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) |
