Exception problem in C++

[ravss2]

I am trying to understand exceptions in C++, below code i was expecting answer 42 32, but somehow it is giving error.

is there any problem here, please help.

#include <iostream>
using namespace std;

class base{
  
  public:
  base() { }
  
    ~base()
    {
        throw 42;
    }
};

int main() 
    {
        
        try {
            base B;
            throw 32;
        }
        catch(int x)
        {
            cout<<x;
        }
    
   return 0;
}

[lastchance]

Change line 42 to
cout << 42;
There is nothing to catch stuff thrown by the base destructor.

[Cubbi]

As of C++11, it is an error to throw from a destructor without declaring it throwing explicitly.

prog.cc: In destructor 'base::~base()':
prog.cc:11:15: warning: throw will always call terminate() [-Wterminate]
   11 |         throw 42;
      |               ^~

which is why when this program runs, it terminates unconditionally.

If you make your destructor throwing (~base() noexcept(false) { throw 42; }),. you will still terminate because the destructor of B will be called during exception handling to handle throw 32;, and throwing an exception while unwinding for another is termination.

You can make it compile and run if you end the lifetime of B before reaching throw 32:

        try {
            base{};
            throw 32;
        }

demo https://wandbox.org/permlink/1fyWsOnfF8KYLBxK

or if you handle the 32 before ending the lifetime of B

        try {
            base B;
            try {
              throw 32;
            } catch(int y) { cout << y; }
        }

demo https://wandbox.org/permlink/wDPtf9ToPSxqX73y

in general, throwing from destructors is considered to be a bad idea and is used very rarely (I know only 3 libraries that do: SOCI, galera, and boost.log)