Re: Challenging GotW 66's moral

From:
Salt_Peter <pj_hern@yahoo.com>
Newsgroups:
comp.lang.c++
Date:
Thu, 27 Dec 2007 09:48:54 -0800 (PST)
Message-ID:
<7f677a12-426a-40aa-a981-22d63717dc33@s19g2000prg.googlegroups.com>
On Dec 27, 4:58 am, Salt_Peter <pj_h...@yahoo.com> wrote:

On Dec 27, 1:54 am, George2 <george4acade...@yahoo.com> wrote:

Hello everyone,

In GotW #66, one of the moral is the exception handler of constructor
should not do any like resource free task. I do not agree. Here is the
quoated moral and my code to prove this moral will have memory leak.

Anything wrong with my analysis?

http://www.gotw.ca/gotw/066.htm

Moral #1: Constructor function-try-block handlers have only one
purpose -- to translate an exception. (And maybe to do logging or some
other side effects.) They are not useful for any other purpose.

[Code]
class A
{
private:

int* p;

public:

    A()
    try
    {
        p = new int[10];

        // there are some other exceptions here

    }
    catch (bad_alloc)
    {
        // do not delete since bad_alloc means memory pointed by p is
not allocated
    }
    catch (...)
    {
        // if we do not delete p, there will be memory leak
        // at this point, we are conflicting with Gotw 66's moral 1
        if (p) delete[] p;


at this point, p would never be 0 (even if the new allocation in ctor
body was not processed yet).
Pointer p, as is, has either a valid address or garbage in it.
As far as that catch block is concerned, it'll always delete [] p.

So how about:

A() : p(0)
try
{
  p = new int[10];}

catch(...)
{
  if (p) delete[] p;

}

have you considered shared_ptr instead of doing decadent new
allocations?


obviously, clarification is required since you can't allocate an array
using boost::shared_ptr.
replace the array with a std:vector or use boost::scoped_array.

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