C++ RAII: Resource Acquisition Is Initialization ScopeFail (c++17)
Example
C++17
Thanks to int std::uncaught_exceptions(), we can implement action which executes only on failure (thrown exception in scope).
Previously bool std::uncaught_exception() just allows to detect if any stack unwinding is running.
#include <exception>
#include <iostream>
template <typename F>
class ScopeFail
{
private:
F f;
int uncaughtExceptionCount = std::uncaught_exceptions();
public:
explicit ScopeFail(const F& f) : f(f) {}
ScopeFail(const ScopeFail&) = delete;
ScopeFail& operator =(const ScopeFail&) = delete;
// f() should not throw, else std::terminate is called.
~ScopeFail() {
if (uncaughtExceptionCount != std::uncaught_exceptions()) {
f();
}
}
};
struct Foo {
~Foo() {
try {
ScopeFail logFailure{[](){std::cout << "Fail 1\n";}};
// Scope succeeds,
// even if Foo is destroyed during stack unwinding
// (so when 0 < std::uncaught_exceptions())
// (or previously std::uncaught_exception() == true)
} catch (...) {
}
try {
ScopeFail logFailure{[](){std::cout << "Failure 2\n";}};
throw std::runtime_error("Failed"); // returned value
// of std::uncaught_exceptions increases
} catch (...) { // returned value of std::uncaught_exceptions decreases
}
}
};
int main()
{
try {
Foo foo;
throw std::runtime_error("Failed"); // std::uncaught_exceptions() == 1
} catch (...) { // std::uncaught_exceptions() == 0
}
}
Output:
Failure 2
