Exception-Handling C++

Question

How do I do this,

I have a class called LargeInteger that stores a number of maxmimum 20 digits. I made the constructor

LargeInteger::LargeInteger(string number){ init(number); }

Now if the number is > LargeInteger::MAX_DIGITS (static const member) i.e 20 i want to not create the object and throw an exception.

I created an class LargeIntegerException{ ... }; and did this

void init(string number) throw(LargeIntegerException);
void LargeInteger::init(string number) throw(LargeIntegerException)
{
    if(number.length > MAX_DIGITS)
    throw LargeIntegerException(LargeIntegerException::OUT_OF_BOUNDS);
    else ......
}

So now i modified the constructor

LargeInteger::LargeInteger(string number)
{ try {init(number);} catch(LargeIntegerExceptione) {...} }

Now I have 2 questions
1.Will the object of this class be created incase an exception is thrown?
2.How to handle it if the above is true?

Luchian Grigore · Accepted Answer · 2012-07-28 00:53:51Z

4

No, if an exception is thrown in the constructor, the object is not constructed (provided you don't catch it, like you do).

So - don't catch the exception, rather let it propagate to the calling context.

IMO, this is the right approach - if the object can't be initialize directly, throw an exception in the constructor and don't create the object.

answered Jul 28, 2012 at 0:53

Luchian Grigore

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2 Comments

Jeffrey Chen Over a year ago

so where do i catch the exception then ?

Luchian Grigore Over a year ago

@JeffreyChen wherever you call the constructor.

jmucchiello · Accepted Answer · 2012-07-28 01:04:35Z

1

There is no reason to catch the exception in the constructor. You want the constructor to fail so something outside the constructor has to catch it. If a constructor exits via exception, no object is created.

LargeInteger(string num) { init(num); } // this is just fine.

answered Jul 28, 2012 at 1:04

jmucchiello

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