Re: Checking whether a pointer has been deleted
Gerhard Menzl wrote:
Edson Manoel wrote:
It depends. You can have invalid references too, e.g:
Not really.
Not really? Consider:
a.cc:
int a = 42 ;
extern int& f() ;
int& b = f() ;
int
g()
{
return b ;
}
int&
f()
{
return a ;
}
b.cc:
extern int g() ;
struct B
{
B() ;
int b ;
}
B objB ;
B::B()
: b( g() )
{
}
Now what is the state of the reference b in a.cc, when g() is
called from the constructor of the static objB, if the
initialization of b.cc occurs before the initialization of a.cc?
More simply, of course:
int&
f()
{
int a = 42 ;
return a ;
}
int
main()
{
int& r = f() ;
// What is the state of r?
}
Or:
int* p = new int( 42 ) ;
int& r = p ;
delete p ;
// What is the state of r?
It's actually pretty easy to get invalid references. With no
undefined behavior as long as you don't use them.
MyClass* p = new myClass();
delete p;
CallByRef(*p);
You invoke undefined behaviour the moment you dereference the
pointer, before the reference is created.
Agreed. Of course, since any behavior is possible, one possible
behavior is thus that you have an invalid reference:-).
But I agree that it's not really a valid example -- a good
compiler, when you compile in debugging mode, *will* abort the
program before creating the reference, and will abort the
program whether you use the reference or not. (A really good
compiler will give you an error message -- but it's far from
trivial to write a compiler that good.)
--
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