Difference between revisions of "cpp/error/throw with nested"
From cppreference.com
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(LWG 2855 (decay), not revboxing) |
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| − | If {{c|std:: | + | If {{c|std::decay<T>::type}} is a non-final non-union class type that is neither {{lc|std::nested_exception}} nor derived from {{lc|std::nested_exception}}, throws an exception of an unspecified type that is publicly derived from both {{lc|std::nested_exception}} and from {{c|std::decay<T>::type}}, and constructed from {{c|std::forward<T>(t)}}. The default constructor of the {{tt|nested_exception}} base class calls {{lc|std::current_exception}}, capturing the currently handled exception object, if any, in a {{lc|std::exception_ptr}}. |
Otherwise, throws {{c|std::forward<T>(t)}}. | Otherwise, throws {{c|std::forward<T>(t)}}. | ||
| − | Requires that {{c|std:: | + | Requires that {{c|std::decay<T>::type}} is {{concept|CopyConstructible}} |
===Parameters=== | ===Parameters=== | ||
Revision as of 15:21, 7 March 2017
| Defined in header <exception>
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| template< class T > [[noreturn]] void throw_with_nested( T&& t ); |
(since C++11) | |
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 Template:concept
Contents |
Parameters
| t | - | the exception object to throw |
Return value
(none)
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 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) |
