Defined in header <exception> | ||
---|---|---|
(1) | ||
bool uncaught_exception() throw(); | (until C++11) | |
bool uncaught_exception() noexcept; | (since C++11) (deprecated in C++17) (removed in C++20) | |
int uncaught_exceptions() noexcept; | (2) | (since C++17) |
std::terminate
or std::unexpected
. In other words, std::uncaught_exception
detects if stack unwinding is currently in progress.Sometimes it's safe to throw an exception even while std::uncaught_exception() == true
. For example, if stack unwinding causes an object to be destructed, the destructor for that object could run code that throws an exception as long as the exception is caught by some catch block before escaping the destructor.
(none).
true
if stack unwinding is currently in progress in this thread.An example where int-returning uncaught_exceptions
is used is the boost.log library: the expression BOOST_LOG(logger) << foo();
first creates a guard object and records the number of uncaught exceptions in its constructor. The output is performed by the guard object's destructor unless foo() throws (in which case the number of uncaught exceptions in the destructor is greater than what the constructor observed).
#include <iostream> #include <exception> #include <stdexcept> struct Foo { int count = std::uncaught_exceptions(); ~Foo() { std::cout << (count == std::uncaught_exceptions() ? "~Foo() called normally\n" : "~Foo() called during stack unwinding\n"); } }; int main() { Foo f; try { Foo f; std::cout << "Exception thrown\n"; throw std::runtime_error("test exception"); } catch (const std::exception& e) { std::cout << "Exception caught: " << e.what() << '\n'; } }
Output:
Exception thrown ~Foo() called during stack unwinding Exception caught: test exception ~Foo() called normally
function called when exception handling fails (function) |
|
(C++11) | shared pointer type for handling exception objects (typedef) |
(C++11) | captures the current exception in a std::exception_ptr (function) |
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