Re: Exceptions & Constructors

From:

Roy <royashish@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 30 Jul 2007 06:09:38 -0700

Message-ID:

<1185800978.637343.302630@w3g2000hsg.googlegroups.com>

On Jul 30, 5:52 pm, Erik Wikstr=F6m <Erik-wikst...@telia.com> wrote:

On 2007-07-30 14:24, Gianni Mariani wrote:

Erik Wikstr=F6m wrote:

On 2007-07-30 13:15, jalqa...@gmail.com wrote:

The constructor in MyClass instantiates many objects pointers through
'new', I would like to implement a way to make sure that the object
has been allocated in memory by catch(ing) the bad_alloc exception
error, but this means that I have to throw this error back from
MyClass constructor, how can I avoid this?

Sure, add a flag to the class that tells if the object was constructed
correctly:

class Foo {
  int* ptrarr[16];
public:
  bool correct;
  Foo() correct(true) {
    try {
      for (size_t i = 0; i < 16; ++i)
        ptrarr[i] = new int();
    } catch(bad_alloc&) {
      correct = false;
    }
  }
};

int main() {
  Foo f;
  if (f.correct == false) {
    // Opps, failed to allocate
  }
}

That code leaks if it fails. Should you not have to delete all of them
or at lease assign a null pointer ?

Actually it does not even compile, I forgot the : in the initialisation
list and have not included the headers for bad_alloc etc. It was more to
show the OP the general idea then to give him/her code that worked, as
an example I don't expect that the OP has an array of pointers but
rather a number of pointers, which should then be initialised to null in
the initialisation list before allocating memory with new. Or perhaps
using some kind of smart pointer.

--
Erik Wikstr=F6m

the lost : in the initialization list had me confused ! :-( , thanks
for clearing this up !
What you have suggested is an elegant way of handling an exception ,
what else is bool used for ?