Defined in header <exception> | ||
|---|---|---|
template< class E > void rethrow_if_nested( const E& e ); | (since C++11) |
If E is not a polymorphic class type, or if std::nested_exception is an inaccessible or ambiguous base class of E, there is no effect.
Otherwise, performs.
if (auto p = dynamic_cast<const std::nested_exception*>(std::addressof(e)))
p->rethrow_nested();| e | - | the exception object to rethrow |
(none).
namespace details {
template <class E>
struct can_dynamic_cast
: std::integral_constant<bool,
std::is_polymorphic<E>::value &&
(!std::is_base_of<std::nested_exception, E>::value ||
std::is_convertible<E*, std::nested_exception*>::value)
> { };
template <class T>
void rethrow_if_nested_impl(const T& e, std::true_type)
{
if(auto nep = dynamic_cast<const std::nested_exception*>(std::addressof(e)))
nep->rethrow_nested();
}
template <class T>
void rethrow_if_nested_impl(const T&, std::false_type) { }
}
template <class T>
void rethrow_if_nested(const T& t){
details::rethrow_if_nested_impl(t, details::can_dynamic_cast<T>());
} |
Demonstrates construction and recursion through a nested exception object.
#include <iostream>
#include <stdexcept>
#include <exception>
#include <string>
#include <fstream>
// 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& e) {
print_exception(e, 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);
}
}Output:
exception: run() failed exception: Couldn't open nonexistent.file exception: basic_ios::clear
|
(C++11) | a mixin type to capture and store current exceptions (class) |
|
(C++11) | throws its argument with std::nested_exception mixed in (function template) |
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