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

[edit]Parameters

(none)

[edit]Return value

[edit]Notes

An example where int-returninguncaught_exceptions is used is theboost.log library: the expressionBOOST_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 unlessfoo() throws (in which case the number of uncaught exceptions in the destructor is greater than what the constructor observed).

std::experimental::scope_fail andstd::experimental::scope_success in LFTS v3 rely on the functionality ofuncaught_exceptions, because their destructors need to do different things that depend on whether is called during stack unwinding.

[edit]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";throwstd::runtime_error("test exception");}catch(conststd::exception& e){std::cout<<"Exception caught: "<< e.what()<<'\n';}}

Exception throwng.~Foo() called during stack unwindingException caught: test exceptionf.~Foo() called normally

[edit]Defect reports

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

[edit]See also

[edit]External links

• In other languages

• Deutsch
• Español
• Français
• Italiano
• 日本語
• Português
• Русский
• 中文