C++ Exceptions std::uncaught_exceptions
Example
c++17
C++17 introduces int std::uncaught_exceptions() (to replace the limited bool std::uncaught_exception()) to know how many exceptions are currently uncaught.
That allows for a class to determine if it is destroyed during a stack unwinding or not.
#include <exception>
#include <string>
#include <iostream>
// Apply change on destruction:
// Rollback in case of exception (failure)
// Else Commit (success)
class Transaction
{
public:
Transaction(const std::string& s) : message(s) {}
Transaction(const Transaction&) = delete;
Transaction& operator =(const Transaction&) = delete;
void Commit() { std::cout << message << ": Commit\n"; }
void RollBack() noexcept(true) { std::cout << message << ": Rollback\n"; }
// ...
~Transaction() {
if (uncaughtExceptionCount == std::uncaught_exceptions()) {
Commit(); // May throw.
} else { // current stack unwinding
RollBack();
}
}
private:
std::string message;
int uncaughtExceptionCount = std::uncaught_exceptions();
};
class Foo
{
public:
~Foo() {
try {
Transaction transaction("In ~Foo"); // Commit,
// even if there is an uncaught exception
//...
} catch (const std::exception& e) {
std::cerr << "exception/~Foo:" << e.what() << std::endl;
}
}
};
int main()
{
try {
Transaction transaction("In main"); // RollBack
Foo foo; // ~Foo commit its transaction.
//...
throw std::runtime_error("Error");
} catch (const std::exception& e) {
std::cerr << "exception/main:" << e.what() << std::endl;
}
}
Output:
In ~Foo: Commit
In main: Rollback
exception/main:Error
