[C++] Static class and exception handling

Hamed · 02-18-2012, 01:34 AM

In the name of Allah the most benefition the most merciful

Peace upon to you

class testA
{
testA(int a,int b) throw (int)
{
throw 227;
}
}

class testB
{
public::
static void init()
{
}
private:
static testA object;
}
testA testB:

bject(92,100);

int main()
{
try {
testB::init();
}
catch (int &e)
printf("exception ocurred");
}

return 0;
}

This isn't my real code but I want to show you I have something like this and I cann't handle the exception.
Please,tell me how to solve this problem

Thanks in advance

millgates · 02-18-2012, 03:43 AM

1) please use [code] ... [/code] tags when posting code.
2) Your code contains a lot of error. It doesn't even compile without modifications.

i) class definitions need to end with a semicolon:

Code:

class testA {
    ...
};

class testB {
    ...
};

ii) if you want to call a constructor of static member testA that is declared within testB, you should make the constructor public:

Code:

class testA
{
public:
    testA(int a,int b) throw (int) { ... }
}

...

testA testB:bject(92,100);

iii) one colon after public is enough:

Code:

class testB
{
public::
    ...
}

iv) your main() is missing a brace:

Code:

int main()
{
    try {
        testB::init();
    }
    catch (int &e) 
    {
        printf("exception ocurred");
    }

    return 0;
}

Anyway, if you fix all the errors, the proram will crash with an unhandled exception error. Why? Just read your code:

Code:

testA testB:bject(92,100);

this is where you initialise your static member. This is actually done before main() is called and therefore not within your try -- catch construct. Why would testB::init, which is in your try block cause an exception being thrown is beyond me.

Nylex · 02-18-2012, 04:06 AM

Is there a reason you can't catch the exception in the constructor?

Hamed · 02-19-2012, 10:59 AM

In the name of Allah the most benefition the most merciful

Peace upon to you
Thanks a lot for reading and correcting my codes and replying.

My crash problem was solved by using static pointer.

Code:

class testA
{
  public:
    testA(int a,int b) throw (int)
  {
    throw 202;
  }
  ~testA() throw (int)
  {
    throw 92;
  }
};

class testB
{
  private:
    static testA *obj;
  public:
    static void init()
    {
      obj = new testA(110,227);
    }
    static void kill()
    {
      delete obj;
    }
};
testA *testB::obj;

int main()
{
  try {
    testB::init();
  }
  catch (int &e) {
    cout << e << ": exception handled" << endl;

  }

  return 0;}
}

jthill · 02-19-2012, 12:59 PM

One thing: throwing from a destructor can take down your entire program. Basically, if exception handling is unwinding the stack and during the unwind a destructor throws, C++ calls terminate() because there's no recursive-exception mechanism -- howitzer-proof error recovery like that is the province of mainframe OS's, which UNIX isn't and C++ can't mandate. Fortunately it's easy enough to avoid, you can build your own by instead leaving instructions for the catch clause if the destruction failure leaves necessary cleanup unfinished and mustn't crash your code`.