Re: Writing Efficient Arguments
gpuchtel a ?crit :
On Jul 10, 8:13 am, Michael DOUBEZ <michael.dou...@free.fr> wrote:
gpuchtel a ?crit :
On Jul 10, 6:41 am, Michael DOUBEZ <michael.dou...@free.fr> wrote:
AFAIK the following code is valid (though UB):
void print(int& i)
{
cout<<&i<<endl;
}
int main()
{
print(*static_cast<int*>(0));
return 0;
}
And prints '0'.
A reference cannot be 'null'. What you did created a tempory int
variable that was initialized to 0 (zero), then a reference to that
temporary variable was passed to the print function, which in turn
printed '0'.
Where did you get that from ? Even if I wanted it, I couldn't pass a
temporary because the ref is not const.
It is perhaps more understandable if you replace by:
int *ptr=NULL;
print(*ptr)
and add in print
++i; //cause segfault;
Michael- Hide quoted text -
- Show quoted text -
I didn't say (or mean) 'you' would pass a temporary, I was implying
what the compiler will do (pass). Simply stated, there is no such
thing as a 'null' reference. All your example does is to create a
reference to a (tempory) int value that contains the value of zero.
Your example of a null pointer is not relevant to the discussion of
the (im)possibility of having a 'null' reference.
I don't understand what you mean and I don't see where is your temporary
or why the compiler will create one.
"*static_cast<int*>(0)" is deferencing an int value at address NULL
(assuming NULL is int promoted to 0). The value is passed into the
function which expect a reference.
If the compiler created a temporary it wouldn't be a reference; it would
be a bug in the compiler because it would not modify my value.
My understanding of a 'null' reference is a reference which reference is
null. As in the following
void print(int& i)
{
assert(&i != NULL ) ; // will trigger in my example
//...
}
The code I originally posted is directly equivalent to:
void print(int* i)
{
cout<<i<<endl;
}
int main()
{
print(static_cast<int*>(0));
return 0;
}
My point is that 'null' reference do exists the same way null pointer
exists.
Michael