Module 14: Copy Construction and Copy Assignment in C++
Overview
Discussion on copy construction and copy assignment operator.
Key Definitions
Copy Construction: Creating a clone of an object that does not exist.
Copy Assignment: Copying another object of the same type into an existing object.
Defined as a function operator taking a const reference of the class and returning a non-const reference (or possibly a const reference).
Copy Assignment Operator
Associated with existing objects.
Can lead to complex issues involving shallow and deep copies.
Shallow vs Deep Copy
Shallow Copy: Copies pointers but not the object it points to. Both pointers refer to the same object.
Deep Copy: Creates a new copy of the object, hence the pointers refer to different objects.
Example with Strings
Objects: S1 ('football') and S2 ('cricket')
Action: S1 = S2
Process: When S1 is assigned S2, a new deep copy is created to avoid memory leaks.
Risks of Self-Copy
Self-copy occurs when an object is assigned to itself, e.g., S1 = S1.
Potential problems: Attempting to copy from a freed memory location can lead to garbage values or crashes.
Handling Self-Copy
Check if the source and destination objects are the same using memory address comparison.
Example: if (this != &S) { /* proceed with assignment */ }
Useful in avoiding deallocation of memory that is still needed.
Basic Structure of Copy Assignment Operator
Signature: Typically includes a self-copy check at the beginning.
Release resources held by the object before assigning new values.
Copy other members of the class to the current object.
Additional Points
The copy constructor is automatically defined by the compiler if not provided but performs a bitwise copy.
Important to always implement custom copy constructors and assignment operators in user-defined classes to ensure correct behavior during copying.
Deep copy is safer but may be costly due to memory and performance overhead.
Conclusion
Understanding copy constructors and copy assignment is crucial in C++ programming, especially in the context of memory management and object life cycles. Proper implementation helps avoid problems like memory leaks and invalid memory access due to self-copying situations.