1. Copy Assignment
CSCE 121
J. Michael Moore

2. Overload ‘=‘ Operator ‘=‘ is the assignment operator
Allows class to perform expected deep copy behavior

3. Using Copy Assignment
MyClass object1, object2; // modify object 1 object2 = object1;

4. Declaration
ClassName& operator=(const ClassName& source); a = b; a.operator=(b);

5. Definition Prevent a memory leak!
ClassName& Classname::operator=(const ClassName& source) { if (this != &source) { // don’t self assign // Delete old data // Allocate new memory // Copy data } return *this;
Prevent a memory leak!

6. Copy Assignment vs. Copy Constructor Return: reference to self
Function name: operator=
Parameter: const reference to source object of same type
Check for self-assignment
Delete old data
Allocate new memory
Copy data from source
Return: None (all constructors)
Function name: ClassName
Parameter: const reference to source object of same type
Allocate new memory
Copy data from source
If we compare the copy assignment operator to the copy constructor, we see first of all that they take the same parameter: a const reference to the source object.
And it we look at what they do, we see that the copy constructor is the same as the copy assignment operator, minus a couple of missing steps that aren’t needed. Now why would we not need to check for self-assignment and delete old data?
... Because the object is just being created, so there’s nothing to delete yet, and it can’t be equal to the source because it’s not initialized yet.