| 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, does nothing.
Otherwise, if dynamic_cast<const std::nested_exception&>(e) would succeed (i.e., if E or the dynamic type (the most derived type) of the object referenced by e is std::nested_exception or publicly and unambiguously derived from std::nested_exception), extracts and throws the nested exception as if by calling dynamic_cast<const std::nested_exception&>(e).rethrow_nested(). Otherwise, does nothing.
| e | - | the exception object to rethrow |
(none).
template <class T>
void rethrow_if_nested(const T& e,
std::enable_if_t<std::is_polymorphic<T>::value>* = 0)
{
if(auto nep = dynamic_cast<const std::nested_exception*>(&e))
nep->rethrow_nested();
}
template <class T>
void rethrow_if_nested(const T&,
std::enable_if_t<!std::is_polymorphic<T>::value>* = 0)
{
} |
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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