exception handling, unexpected terminator in c++

Question

Following code is about exception handling. I got the output:

Botch::f()
I'll be back!

Why Fruit is not caught? Thanks!

Ignore this. I think I have provided enough detail.

#include <exception>
#include <iostream>
using namespace std;

void terminator() {
    cout << "I'll be back!" << endl;
    exit(0);
}

void (*old_terminate)() = set_terminate(terminator);

class Fruit {};

class Botch {
public:
    void f() throw(Fruit, bad_exception) {
        cout << "Botch::f()" << endl;
        throw Fruit();
    }
    ~Botch() { throw 'c'; }
};

int main() {
    try{
        Botch b;
        b.f();
    } catch(Fruit&) {
        cout << "inside catch(Fruit)" << endl;
    } catch(bad_exception&) {
        cout << "caught a bad_excpetionfrom f" << endl;
    }
}

Answer 1

Because during stack unwinding for your Fruit exception you threw another exception (from the Botch destructor). So your terminator was called instead. This is why throwing exceptions from a destructor is a bad idea,

Answer 2

Fruit is not caught because the code never reaches that catch clause. In the try block in main , the call to bf() throws an exception of type Fruit . In response, the code destroys the Botch object before entering the catch clause. The destructor of Botch throws another exception, and that triggers the call to terminate .

Answer 3

When bf() is called in main, a Fruit is thrown. Then execution leaves the try block, and before any catch handler can catch that Fruit , b is destroyed and 'c' is thrown. Throwing a second exception while the Fruit is still active leads to termination, regardless of any catch handlers.
This is the reason why you never shall throw from destructors.

Answer 4

because the program flow is as follows:

try{
        Botch b;
        b.f();
        //-> exception of class Fruit has been thrown
        //-> Stack unwinding: during stack unwinding object b, 
        //which is on stack is destroyed, and its destructor is called
        //-> this destructor ~Botch() { throw 'c'; } throws another exception 
        //and this caused call of your terminator()
    } catch(Fruit&) {  // so we are never here