Re: The history of delete on null pointers
Jorgen Grahn wrote:
Out of curiosity and frustration: was there ever a point in time when it
wasn't safe to pass a null pointer to delete?
I constantly find, in other people's code, things on the form
void foo(Bar * bar)
{
// ...
if(bar) delete(bar);
}
and I wonder what's behind it. History or psychology? Last time I needed
to do something similar myself was with AmigaDOS's FreeMem() system call,
some fifteen years ago ...
I read that code as effectively documenting that bar could be NULL at the
point of the delete. It strikes me as unusual, not because the check is
strictly speaking not necessary, but because in most designs the lifetime
of an object is explicitly known so at the point of delete you know for
sure the pointer is not NULL. If the design really does call for an object
with lifetime controlled by foo(), but also is allowed to be NULL, I would
expect something more like
void foo(Bar*& bar)
{
// ...
if (bar)
{
delete bar;
bar = NULL;
}
}
Nevertheless, I still wouldn't bother with the guard myself (except if bar
== NULL was the common case, it might be faster with the guard), the
assignment of bar already has the implication that bar will be reused later
when it could be NULL.
Cheers,
Ian McCulloch
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