Copy Constructor in C++ vs. Assignment Operator in C++ — What's the Difference?
By Tayyaba Rehman & Urooj Arif — Published on February 6, 2024
Copy Constructor in C++ creates a new object as a copy of an existing object. Assignment Operator in C++ assigns the values from one existing object to another already existing object.
Difference Between Copy Constructor in C++ and Assignment Operator in C++
Table of Contents
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Key Differences
The Copy Constructor in C++ is used during the creation of an object to initialize it with values from another object of the same class. The Assignment Operator in C++, on the other hand, is used to copy values to an already existing object from another object of the same class.
Copy Constructor in C++ is called when a new object is created from an existing object, as a copy of the existing object. In contrast, the Assignment Operator in C++ is used when an already initialized object is assigned a new value from another existing object.
A Copy Constructor in C++ may be called implicitly in several scenarios, such as passing objects by value. The Assignment Operator in C++ is explicitly called when an assignment operation occurs between two existing objects.
The Copy Constructor in C++ is crucial for classes that have pointers or dynamic resources, to ensure a deep copy. For the Assignment Operator in C++, it's essential to handle self-assignment and ensure proper resource management, often using the copy-and-swap idiom.
Copy Constructor in C++ can be used to create a new object based on the state of an existing object, thereby not altering the existing object. The Assignment Operator in C++, however, typically alters the state of the object it is assigned to, replacing its current state with that of another object.
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Comparison Chart
Purpose
Initializes new object with another object's values
Assigns values from one object to another existing object
Usage Scenario
Called when creating a new object
Used on already initialized objects
Functionality
Creates a copy of an object upon creation
Overwrites an object's existing values
Handling Resources
Ensures proper initialization of resources
Manages resource allocation and avoids self-assignment
Implicit/Explicit Call
Often called implicitly
Called explicitly during assignment
Compare with Definitions
Copy Constructor in C++
Used for initializing one object from another during object creation.
MyClass newObj(existingObj); uses the copy constructor for initialization.
Assignment Operator in C++
Used for copying data to an already initialized object.
MyClass obj1; obj1 = obj2; copies obj2 to obj1.
Copy Constructor in C++
Initializes an object by copying data from another object of the same class.
MyClass obj1(obj2); creates obj1 as a copy of obj2.
Assignment Operator in C++
Often implemented using the copy-and-swap idiom for exception safety.
Obj1 = std::move(obj2); uses assignment operator with copy-and-swap.
Copy Constructor in C++
Invoked when returning an object from a function by value.
Return myObject; in a function invokes the copy constructor for myObject.
Assignment Operator in C++
Overwrites an object's existing data with another object's data.
ExistingObj = newObj; replaces existingObj's data with newObj's.
Copy Constructor in C++
Copy Constructor is called when passing an object by value.
Void function(MyClass obj) calls the copy constructor for obj.
Assignment Operator in C++
Assigns values from one object to another of the same class.
Obj1 = obj2; assigns values of obj2 to obj1.
Copy Constructor in C++
It's essential for deep copying in classes with dynamic memory allocation.
MyClass obj1 = obj2; allocates separate memory for obj1's resources.
Assignment Operator in C++
Typically includes handling of self-assignment and resource management.
Obj = obj; safely handles self-assignment.
Common Curiosities
What is the role of the Assignment Operator in C++?
It assigns values from one existing object to another.
Is the Copy Constructor in C++ implicitly called?
Yes, it's often called implicitly in various scenarios.
What does a Copy Constructor in C++ do?
It initializes a new object as a copy of an existing object.
Can the Copy Constructor in C++ handle dynamic resources?
Yes, it's essential for handling dynamic resources and ensuring deep copies.
Can the Assignment Operator in C++ be called implicitly?
No, it's explicitly called during an assignment operation.
When is the Copy Constructor in C++ called?
During the creation of an object, passing objects by value, or returning objects from functions.
How does the Copy Constructor in C++ affect the existing object?
It doesn't alter the existing object, just creates a new copy.
Can Copy Constructor in C++ be overridden?
Yes, a custom copy constructor can be defined.
What happens if no Copy Constructor is defined in C++?
The compiler provides a default shallow copy constructor.
How does the Assignment Operator in C++ differ in usage?
It's used for assigning values between two already existing objects.
What's the default behavior of the Assignment Operator in C++?
By default, it performs a shallow copy of non-static members.
How do Copy Constructor and Assignment Operator in C++ manage memory?
Both must handle memory management carefully, especially for deep copying in classes with dynamic memory.
Does the Assignment Operator in C++ alter the object it's assigned to?
Yes, it replaces the current state of the object with that of another object.
What special considerations are there for the Assignment Operator in C++?
It should handle self-assignment and manage resources, often using the copy-and-swap idiom.
Is overriding the Assignment Operator in C++ common?
Yes, especially in classes with dynamic resources or complex copying logic.
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Written by
Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
Co-written by
Urooj ArifUrooj is a skilled content writer at Ask Difference, known for her exceptional ability to simplify complex topics into engaging and informative content. With a passion for research and a flair for clear, concise writing, she consistently delivers articles that resonate with our diverse audience.
