std::uncaught_exception, std::uncaught_exceptions

Sometimes it's safe to throw an exception even while std::uncaught_exception() == true (until C++17) std::uncaught_exceptions() > 0 (since C++17) . For example, if stack unwinding

Parameters

(none)

Return value

Notes

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()

std::experimental::scope_fail and std::experimental::scope_success in LFTS v3 rely on the functionality of uncaught_exceptions

Example

#include <exception>
#include <iostream>
#include <stdexcept>
 
struct Foo
{
    char id{'?'};
    int count = std::uncaught_exceptions();
 
    ~Foo()
    {
        count == std::uncaught_exceptions()
            ? std::cout << id << ".~Foo() called normally\n"
            : std::cout << id << ".~Foo() called during stack unwinding\n";
    }
};
 
int main()
{
    Foo f{'f'};
 
    try
    {
        Foo g{'g'};
        std::cout << "Exception thrown\n";
        throw std::runtime_error("test exception");
    }
    catch (const std::exception& e)
    {
        std::cout << "Exception caught: " << e.what() << '\n';
    }
}

Exception thrown
g.~Foo() called during stack unwinding
Exception caught: test exception
f.~Foo() called normally

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also

External links