std::throw_with_nested - cppreference.com (original) (raw)

| | | | | ------------------------------------------------------------------------ | | ------------------------------------- | | 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.

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[edit] Example

Demonstrates construction and recursion through a nested exception object.

#include #include #include #include #include   // 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

[edit] See also