There are six flavors each of new and
delete, so make certain that you're using the right
ones. Here are quickie descriptions of new:
single object form, throwing a
bad_alloc on errors; this is what most
people are used to using
Single object "nothrow" form, returning NULL on errors
Array new, throwing
bad_alloc on errors
Array nothrow new, returning
NULL on errors
Placement new, which does nothing (like
it's supposed to)
Placement array new, which also does
nothing
They are distinguished by the parameters that you pass to them, like
any other overloaded function. The six flavors of delete
are distinguished the same way, but none of them are allowed to throw
an exception under any circumstances anyhow. (They match up for
completeness' sake.)
Remember that it is perfectly okay to call delete on a
NULL pointer! Nothing happens, by definition. That is not the
same thing as deleting a pointer twice.
By default, if one of the “throwing news” can't
allocate the memory requested, it tosses an instance of a
bad_alloc exception (or, technically, some class derived
from it). You can change this by writing your own function (called a
new-handler) and then registering it with set_new_handler():
typedef void (*PFV)(void);
static char* safety;
static PFV old_handler;
void my_new_handler ()
{
delete[] safety;
popup_window ("Dude, you are running low on heap memory. You"
" should, like, close some windows, or something."
" The next time you run out, we're gonna burn!");
set_new_handler (old_handler);
return;
}
int main ()
{
safety = new char[500000];
old_handler = set_new_handler (&my_new_handler);
...
}
bad_alloc is derived from the base exception
class defined in Sect1 19.