Re: delete the dynamically allocated memory twice causes error
On Jul 25, 3:10 am, Junhui Tong <tongjun...@live.com> wrote:
tom wrote:
why delete the dynamically allocated memory twice causes an error, see
the code below:
int _tmain(int argc, _TCHAR* argv[])
{
int *pi = new int(12);
cout<<*pi;
delete pi;
delete pi;
}
Well, there exists a C++ implementation which *is able to*
check whether a pointer is valid and safe to delete, but that
will lose some efficiency. For the same reason, C++ won't set
the pointer to `NULL' after delete.
The main reason here has nothing to do with efficiency. It has
to do with the fact that it doesn't buy you anything, and even
more so with the fact that the "pointer" isn't necessarily an
lvalue which can be modified. (I'd say that over half my
deletes are "delete this".)
Another example is that C++ also won't check whether an array
index is out of bound.
C++ leaves that up to the implementation. A good implementation
will check, at least in the case where it knows the bounds.
You know, C++ won't do anything which make programmer easier
but lose efficiency.
C++ (like C) leaves much behavior undefined intentionally just
so that an implementation can check (but isn't required to).
Good implementations do check, when it is reasonable to do so.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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