比较自我分配的指针

Question

I am trying to overload the = operator on a simple C++ class called Set that contains a dynamic array of ints. For the = operator, I first want to check for self assignment, so I wanted to compare 2 pointers to make see if they have the same memory address. Here's the code:

Set& Set::operator=(const Set& setEqual)
{
//first check for self assignment
if(setEqual == this*)
    cout << "this is self assignment";
}

The error spat out is error: expected primary-expression before ')' token

I believe I'm having a misunderstanding of pointers again, so if anyone could point (ha!) me in the right direction, I'd appreciate it.

Answer 1

The error is becuase this* is not valid - * is either infix (in multiplication) or prefix (in dereferencing pointers).

You probably want &setEqual == this - that is assigning from an object at the same memory address or setEqual==*this - comparing equality using whatever operator== you have defined

Answer 2

If you want to compare the address of the thing pointed too you really want this:

Set& Set::operator=(const Set& setEqual)
{
//first check for self assignment
if(&setEqual == this)
    cout << "this is self assignment";
}

Using (setEqual==*this) as sugested by some of the solutions compares if the objects are equal under operator== .

Answer 3

To detect self-assignment you need

if(&setEqual == this)

you should never use

if(setEqual == *this)

for detecting self-assignment as the latter statement will invoke comparison of the objects, which might be overloaded in the way you don't expect and is likely slower as well.