difference between copy constructor and assignment operator

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Difference Between Copy Constructor and Assignment Operator in C++

Let us study the difference between the copy constructor and assignment operator.

Content: Copy Constructor Vs Assignment Operator

Comparison chart.

• Key Differences

Definition of Copy Constructor

A “copy constructor” is a form of an overloaded constructor . A copy constructor is only called or invoked for initialization purpose. A copy constructor initializes the newly created object by another existing object.

When a copy constructor is used to initialize the newly created target object, then both the target object and the source object shares a different memory location. Changes done to the source object do not reflect in the target object. The general form of the copy constructor is

If the programmer does not create a copy constructor in a C++ program, then the compiler implicitly provides a copy constructor. An implicit copy constructor provided by the compiler does the member-wise copy of the source object. But, sometimes the member-wise copy is not sufficient, as the object may contain a pointer variable.

Copying a pointer variable means, we copy the address stored in the pointer variable, but we do not want to copy address stored in the pointer variable, instead, we want to copy what pointer points to. Hence, there is a need of explicit ‘copy constructor’ in the program to solve this kind of problems.

A copy constructor is invoked in three conditions as follow:

• Copy constructor invokes when a new object is initialized with an existing one.
• The object passed to a function as a non-reference parameter.
• The object is returned from the function.

Let us understand copy constructor with an example.

In the code above, I had explicitly declared a constructor “copy( copy &c )”. This copy constructor is being called when object B is initialized using object A. Second time it is called when object C is being initialized using object A.

When object D is initialized using object A the copy constructor is not called because when D is being initialized it is already in the existence, not the newly created one. Hence, here the assignment operator is invoked.

Definition of Assignment Operator

The assignment operator is an assigning operator of C++.  The “=” operator is used to invoke the assignment operator. It copies the data in one object identically to another object. The assignment operator copies one object to another member-wise. If you do not overload the assignment operator, it performs the bitwise copy. Therefore, you need to overload the assignment operator.

In above code when object A is assigned to object B the assignment operator is being invoked as both the objects are already in existence. Similarly, same is the case when object C is initialized with object A.

When the bitwise assignment is performed both the object shares the same memory location and changes in one object reflect in another object.

Key Differences Between Copy Constructor and Assignment Operator

• A copy constructor is an overloaded constructor whereas an assignment operator is a bitwise operator.
• Using copy constructor you can initialize a new object with an already existing object. On the other hand, an assignment operator copies one object to the other object, both of which are already in existence.
• A copy constructor is initialized whenever a new object is initialized with an already existing object, when an object is passed to a function as a non-reference parameter, or when an object is returned from a function. On the other hand, an assignment operator is invoked only when an object is being assigned to another object.
• When an object is being initialized using copy constructor, the initializing object and the initialized object shares the different memory location. On the other hand, when an object is being initialized using an assignment operator then the initialized and initializing objects share the same memory location.
• If you do not explicitly define a copy constructor then the compiler provides one. On the other hand, if you do not overload an assignment operator then a bitwise copy operation is performed.

The Copy constructor is best for copying one object to another when the object contains raw pointers.

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Copy Constructor in C++

A copy constructor is a type of constructor that initializes an object using another object of the same class. In simple terms, a constructor which creates an object by initializing it with an object of the same class, which has been created previously is known as a copy constructor .  

The process of initializing members of an object through a copy constructor is known as copy initialization . It is also called member-wise initialization because the copy constructor initializes one object with the existing object, both belonging to the same class on a member-by-member copy basis.

Syntax of Copy Constructor in C++

Copy constructor takes a reference to an object of the same class as an argument:

Here, the const qualifier is optional but is added so that we do not modify the obj by mistake.

Syntax of Copy Constructor

Examples of Copy Constructor in C++

Example 1: user defined copy constructor.

If the programmer does not define the copy constructor, the compiler does it for us.

Example 2: Default Copy Constructor

An implicitly defined copy constructor will copy the bases and members of an object in the same order that a constructor would initialize the bases and members of the object.

Need of User Defined Copy Constructor

If we don’t define our own copy constructor, the C++ compiler creates a default copy constructor for each class which works fine in general. However, we need to define our own copy constructor only if an object has pointers or any runtime allocation of the resource like a file handle , a network connection, etc because the default constructor does only shallow copy.

Shallow Copy means that only the pointers will be copied not the actual resources that the pointers are pointing to. This can lead to dangling pointers if the original object is deleted.

Deep copy is possible only with a user-defined copy constructor. In a user-defined copy constructor, we make sure that pointers (or references) of copied objects point to new copy of the dynamic resource allocated manually in the copy constructor using new operators.

Example: Class Where a Copy Constructor is Required

Following is a complete C++ program to demonstrate the use of the Copy constructor. In the following String class, we must write a copy constructor. 

Note: Such classes also need the overloaded assignment operator. See this article for more info – C++ Assignment Operator Overloading

What would be the problem if we remove the copy constructor from the above code?

If we remove the copy constructor from the above program, we don’t get the expected output. The c hanges made to str2 reflect in str1 as well which is never expected. Also, if the str1 is destroyed, the str2’s data member s will be pointing to the deallocated memory.

When is the Copy Constructor Called?

In C++, a copy constructor may be called in the following cases: 

• When an object of the class is returned by value.
• When an object of the class is passed (to a function) by value as an argument.
• When an object is constructed based on another object of the same class.
• When the compiler generates a temporary object.

It is, however, not guaranteed that a copy constructor will be called in all these cases, because the C++ Standard allows the compiler to optimize the copy away in certain cases, one example is the return value optimization (sometimes referred to as RVO).

Refer to this article for more details – When is a Copy Constructor Called in C++?

Copy Elision

In copy elision, the compiler prevents the making of extra copies by making the use to techniques such as NRVO and RVO which results in saving space and better the program complexity (both time and space); Hence making the code more optimized.

Copy Constructor vs Assignment Operator

The main difference between Copy Constructor and Assignment Operator is that the Copy constructor makes a new memory storage every time it is called while the assignment operator does not make new memory storage.

Which of the following two statements calls the copy constructor and which one calls the assignment operator? 

A copy constructor is called when a new object is created from an existing object, as a copy of the existing object. The assignment operator is called when an already initialized object is assigned a new value from another existing object. In the above example (1) calls the copy constructor and (2) calls the assignment operator.

Frequently Asked Questions in C++ Copy Constructors

Can we make the copy constructor private  .

Yes, a copy constructor can be made private. When we make a copy constructor private in a class, objects of that class become non-copyable. This is particularly useful when our class has pointers or dynamically allocated resources. In such situations, we can either write our own copy constructor like the above String example or make a private copy constructor so that users get compiler errors rather than surprises at runtime.

Why argument to a copy constructor must be passed as a reference?  

If you pass the object by value in the copy constructor, it will result in a recursive call to the copy constructor itself. This happens because passing by value involves making a copy, and making a copy involves calling the copy constructor, leading to an infinite recursion. Using a reference avoids this recursion. So, we use reference of objects to avoid infinite calls.

Why argument to a copy constructor should be const?

One reason for passing const reference is, that we should use const in C++ wherever possible so that objects are not accidentally modified. This is one good reason for passing reference as const , but there is more to it than ‘ Why argument to a copy constructor should be const?’

Related Articles:

• Constructors in C++

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What's the difference between assignment operator and copy constructor in C++?

The Copy constructor and the assignment operators are used to initialize one object to another object. The main difference between them is that the copy constructor creates a separate memory block for the new object. But the assignment operator does not make new memory space. It uses reference variable to point to the previous memory block.

Copy Constructor (Syntax)

Assignment operator (syntax).

Let us see the detailed differences between Copy constructor and Assignment Operator.

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Copy Constructors and Assignment Operators: Just Tell Me the Rules! Part I

I get asked this question sometimes from seasoned programmers who are new to C++. There are plenty of good books written on the subject, but I found no clear and concise set of rules on the Internet for those who don’t want to understand every nuance of the language—and just want the facts.

Hence this article.

The purpose of copy constructors and assignment operators is easy to understand when you realize that they’re always there even if you don’t write them, and that they have a default behavior that you probably already understand. Every struct and class have a default copy constructor and assignment operator method. Look at a simple use of these.

Start with a struct called Rect with a few fields:

Yes, even a struct as simple as this has a copy constructor and assignment operator. Now, look at this code:

Line 2 invokes the default copy constructor for r2, copying into it the members from r1. Line 3 does something similar, but invokes the default assignment operator of r3, copying into it the members from r1. The difference between the two is that the copy constructor of the target is invoked when the source object is passed in at the time the target is constructed, such as in line 2. The assignment operator is invoked when the target object already exists, such as on line 4.

Looking at what the default implementation produces, examine what Line 4 ends up doing:

So, if the default copy constructor and assignment operators do all this for you, why would anyone implement their own? The problem with the default implementations is that a simple copy of the members may not be appropriate to clone an object. For instance, what if one of the members were a pointer that is allocated by the class? Simply copying the pointer isn’t enough because now you’ll have two objects that have the same pointer value, and both objects will try to free the memory associated with that pointer when they destruct. Look at an example class:

Now, look at some code that uses this class:

The problem is, c1 and c2 will have the same pointer value for the “name” field. When c2 goes out of scope, its destructor will get called and delete the memory that was allocated when c1 was constructed (because the name field of both objects have the same pointer value). Then, when c1 destructs, it will attempt to delete the pointer value, and a “double-free” occur. At best, the heap will catch the problem and report an error. At worst, the same pointer value may, by then, be allocated to another object, the delete will free the wrong memory, and this will introduce a difficult-to-find bug in the code.

The way you want to solve this is by adding an explicit copy constructor and an assignment operator to the class, like so:

Now, the code that uses the class will function properly. Note that the difference between the copy constructor and assignment operator above is that the copy constructor can assume that fields of the object have not been set yet (because the object is just being constructed). However, the assignment operator must handle the case when the fields already have valid values. The assignment operator deletes the contents of the existing string before assigning the new string. You might ask why the tempName local variable is used, and why the code isn’t written as follows instead:

The problem with this code is that if the new operator throws an exception, the object will be left in a bad state because the name field would have already been freed by the previous instruction. By performing all the operations that could fail first and then replacing the fields once there’s no chance of an exception from occurring, the code is exception safe.

Note: The reason the assignment operator returns a reference to the object is so that code such as the following will work: c1 = c2 = c3;

One might think that the case when an explicit copy constructor and assignment operator methods are necessary is when a class or struct contains pointer fields. This is not the case. In the case above, the explicit methods were needed because the data pointed to by the field is owned by the object. If the pointer is a “back” (or weak) pointer, or a reference to some other object that the class is not responsible for releasing, it may be perfectly valid to have more than one object share the value in a pointer field.

There are times when a class field actually refers to some entity that cannot be copied, or it does not make sense to be copied. For instance, what if the field were a handle to a file that it created? It’s possible that copying the object might require that another file be created that has its own handle. But, it’s also possible that more than one file cannot be created for the given object. In this case, there cannot be a valid copy constructor or assignment operator for the class. As you have seen earlier, simply not implementing them does not mean that they won’t exist, because the compiler supplies the default versions when explicit versions aren’t specified. The solution is to provide copy constructors and assignment operators in the class and mark them as private. As long as no code tries to copy the object, everything will work fine, but as soon as code is introduced that attempts to copy the object, the compiler will indicate an error that the copy constructor or assignment operator cannot be accessed.

To create a private copy constructor and assignment operator, one does not need to supply implementation for the methods. Simply prototyping them in the class definition is enough. Example:

Some people wish that C++ did not provide an implicit copy constructor and assignment operator if one isn’t provided. They automatically define a private copy constructor and assignment operator automatically when they define a new class. That way, it will prevent anyone from copying their object unless the explicitly support such an operation. This is generally a good practice.

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Home » Technology » IT » Programming » What is the Difference Between Copy Constructor and Assignment Operator

What is the Difference Between Copy Constructor and Assignment Operator

The main difference between copy constructor and assignment operator is that copy constructor is a type of constructor that helps to create a copy of an already existing object without affecting the values of the original object while assignment operator is an operator that helps to assign a new value to a variable in the program.

A constructor is a special method that helps to initialize an object when creating it. It has the same name as the class name and has no return type. A programmer can write a constructor to give initial values to the instance variables in the class. If there is no constructor in the program, the default constructor will be called. Copy constructor is a type of constructor that helps to create a copy of an existing object. On the other hand, assignment operator helps to assign a new value to a variable.

Key Areas Covered

1. What is Copy Constructor      – Definition, Functionality 2. What is Assignment Operator      – Definition, Functionality 3. What is the Difference Between Copy Constructor and Assignment Operator      – Comparison of Key Differences

Constructor, Copy Constructor, Assignment Operator, Variable

What is Copy Constructor

In programming, sometimes it is necessary to create a separate copy of an object without affecting the original object. Copy constructor is useful in these situations. It allows creating a replication of an existing object of the same class. Refer the below example.

Figure 1: Program with copy constructor

The class Triangle has two instance variables called base and height. In line 8, there is a parameterized constructor. It takes two arguments. These values are assigned to the instance variables base and height. In line 13, there is a copy constructor. It takes an argument of type Triangle. New object’s base value is assigned to the instance variable base. Similarly, the new object’s height value is assigned to the instance variable height. Furthermore, there is a method called calArea to calculate and return area.

In the main method, t1 and t2 are Triangle objects. The object t1 is passed when creating the t2 object. The copy constructor is called to create t2 object. Therefore, the base and the height of the t2 object is the same as the base and height of t1 object. Finally, both objects have the same area.    

What is Assignment Operator

An assignment operator is useful to assign a new value to a variable. The assignment operator is “=”.  When there is a statement as c = a + b; the summation of ‘a’ and ‘b’ is assigned to the variable ‘c’.

Figure 2: Program with assignment operator

The class Number has an instance variable called num. There is a no parameter constructor in line 7. However, there is a parameterized constructor in line 9. It takes an argument and assigns it to the instance variable using the assignment operator. In line 12, there is a method called display to display the number. In the main method, num1 and num2 are two objects of type Number. Printing num1 and num2 gives the references to those objects. The num3 is of type Number. In line 24, num1 is assigned to num3 using the assignment operator. Therefore, num3 is referring to num1 object. So, printing num3 gives the num1 reference.  

The assignment operator and its variations are as follows.

Difference Between Copy Constructor and Assignment Operator

Copy constructor is a special constructor for creating a new object as a copy of an existing object. In contrast, assignment operator is an operator that is used to assign a new value to a variable. These definitions explain the basic difference between copy constructor and assignment operator.

Functionality with Objects

Functionality with objects is also a major difference between copy constructor and assignment operator. Copy constructor initializes the new object with an already existing object while assignment operator assigns the value of one object to another object which is already in existence.

Copy constructor helps to create a copy of an existing object while assignment operator helps to assign a new value to a variable. This is another difference between copy constructor and assignment operator.

The difference between copy constructor and assignment operator is that copy constructor is a type of constructor that helps to create a copy of an already existing object without affecting the values of the original object while assignment operator is an operator that helps to assign a new value to a variable in the program.

1. Thakur, Dinesh. “Copy Constructor in Java Example.” Computer Notes, Available here .

About the Author: Lithmee

Lithmee holds a Bachelor of Science degree in Computer Systems Engineering and is reading for her Master’s degree in Computer Science. She is passionate about sharing her knowldge in the areas of programming, data science, and computer systems.

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Copy assignment operator.

A copy assignment operator is a non-template non-static member function with the name operator = that can be called with an argument of the same class type and copies the content of the argument without mutating the argument.

[ edit ] Syntax

For the formal copy assignment operator syntax, see function declaration . The syntax list below only demonstrates a subset of all valid copy assignment operator syntaxes.

[ edit ] Explanation

The copy assignment operator is called whenever selected by overload resolution , e.g. when an object appears on the left side of an assignment expression.

[ edit ] Implicitly-declared copy assignment operator

If no user-defined copy assignment operators are provided for a class type, the compiler will always declare one as an inline public member of the class. This implicitly-declared copy assignment operator has the form T & T :: operator = ( const T & ) if all of the following is true:

• each direct base B of T has a copy assignment operator whose parameters are B or const B & or const volatile B & ;
• each non-static data member M of T of class type or array of class type has a copy assignment operator whose parameters are M or const M & or const volatile M & .

Otherwise the implicitly-declared copy assignment operator is declared as T & T :: operator = ( T & ) .

Due to these rules, the implicitly-declared copy assignment operator cannot bind to a volatile lvalue argument.

A class can have multiple copy assignment operators, e.g. both T & T :: operator = ( T & ) and T & T :: operator = ( T ) . If some user-defined copy assignment operators are present, the user may still force the generation of the implicitly declared copy assignment operator with the keyword default . (since C++11)

The implicitly-declared (or defaulted on its first declaration) copy assignment operator has an exception specification as described in dynamic exception specification (until C++17) noexcept specification (since C++17)

Because the copy assignment operator is always declared for any class, the base class assignment operator is always hidden. If a using-declaration is used to bring in the assignment operator from the base class, and its argument type could be the same as the argument type of the implicit assignment operator of the derived class, the using-declaration is also hidden by the implicit declaration.

[ edit ] Implicitly-defined copy assignment operator

If the implicitly-declared copy assignment operator is neither deleted nor trivial, it is defined (that is, a function body is generated and compiled) by the compiler if odr-used or needed for constant evaluation (since C++14) . For union types, the implicitly-defined copy assignment copies the object representation (as by std::memmove ). For non-union class types, the operator performs member-wise copy assignment of the object's direct bases and non-static data members, in their initialization order, using built-in assignment for the scalars, memberwise copy-assignment for arrays, and copy assignment operator for class types (called non-virtually).

[ edit ] Deleted copy assignment operator

An implicitly-declared or explicitly-defaulted (since C++11) copy assignment operator for class T is undefined (until C++11) defined as deleted (since C++11) if any of the following conditions is satisfied:

• T has a non-static data member of a const-qualified non-class type (or possibly multi-dimensional array thereof).
• T has a non-static data member of a reference type.
• T has a potentially constructed subobject of class type M (or possibly multi-dimensional array thereof) such that the overload resolution as applied to find M 's copy assignment operator
• does not result in a usable candidate, or
• in the case of the subobject being a variant member , selects a non-trivial function.

[ edit ] Trivial copy assignment operator

The copy assignment operator for class T is trivial if all of the following is true:

• it is not user-provided (meaning, it is implicitly-defined or defaulted);
• T has no virtual member functions;
• T has no virtual base classes;
• the copy assignment operator selected for every direct base of T is trivial;
• the copy assignment operator selected for every non-static class type (or array of class type) member of T is trivial.

A trivial copy assignment operator makes a copy of the object representation as if by std::memmove . All data types compatible with the C language (POD types) are trivially copy-assignable.

[ edit ] Eligible copy assignment operator

Triviality of eligible copy assignment operators determines whether the class is a trivially copyable type .

[ edit ] Notes

If both copy and move assignment operators are provided, overload resolution selects the move assignment if the argument is an rvalue (either a prvalue such as a nameless temporary or an xvalue such as the result of std::move ), and selects the copy assignment if the argument is an lvalue (named object or a function/operator returning lvalue reference). If only the copy assignment is provided, all argument categories select it (as long as it takes its argument by value or as reference to const, since rvalues can bind to const references), which makes copy assignment the fallback for move assignment, when move is unavailable.

It is unspecified whether virtual base class subobjects that are accessible through more than one path in the inheritance lattice, are assigned more than once by the implicitly-defined copy assignment operator (same applies to move assignment ).

See assignment operator overloading for additional detail on the expected behavior of a user-defined copy-assignment operator.

[ edit ] Example

[ edit ] defect reports.

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[ edit ] See also

• converting constructor
• copy constructor
• copy elision
• default constructor
• aggregate initialization
• constant initialization
• copy initialization
• default initialization
• direct initialization
• initializer list
• list initialization
• reference initialization
• value initialization
• zero initialization
• move assignment
• move constructor
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21.12 — Overloading the assignment operator

Difference Between Copy Constructor and Assignment Operator in C++

In C++, constructors and assignment operators play critical roles in object initialization and memory management. It is crucial to understand the difference between the copy constructor and assignment operator for efficient programming.

The C++ language provides special member functions for creating and manipulating objects. Copy constructor and assignment operator are two such functions used for object copying and assignment.

The copy constructor is used to create a new object as a copy of an existing object, while the assignment operator is used to assign the value of one object to another object of the same class.

Table of Contents

Key Takeaways

What is a copy constructor in c++, what is an assignment operator in c++, key differences between copy constructor and assignment operator, object copying: deep copy vs shallow copy, syntax and usage: copy constructor, syntax and usage: assignment operator, when to use copy constructor, when to use assignment operator, example: copy constructor in c++, example: assignment operator in c++, understanding copy constructor and assignment operator in c++, c++ copy constructor and assignment operator distinction, difference between copy constructor and assignment operator in c++ with examples, copy constructor example, assignment operator example, c++ memory management: deep copy vs shallow copy, q: what is the difference between a copy constructor and an assignment operator in c++, q: what is a copy constructor in c++, q: what is an assignment operator in c++, q: what are the key differences between a copy constructor and an assignment operator, q: what is the difference between deep copy and shallow copy in object copying, q: what is the syntax and usage of a copy constructor in c++, q: what is the syntax and usage of an assignment operator in c++, q: when should a copy constructor be used, q: when should an assignment operator be used, q: can you provide an example of a copy constructor in c++, q: can you provide an example of an assignment operator in c++, q: how can i understand the copy constructor and assignment operator in c++, q: what is the distinction between the copy constructor and assignment operator in c++, q: can you explain the difference between the copy constructor and assignment operator in c++ with examples, q: how does memory management differ between deep copy and shallow copy in c++.

• The copy constructor and assignment operator are essential for object copying and assignment in C++.
• Understanding the difference between the two functions is crucial for efficient programming.
• C++ provides specific rules and conventions for syntax and usage of these functions.

In C++, object initialization is a critical aspect of memory management. A copy constructor is a special member function that is used to create a new object as a copy of an existing object. When a new object is being initialized with an existing object, the copy constructor is invoked.

The copy constructor is used to create a deep copy of an object. A deep copy means that a new copy of an object is created along with any dynamically allocated memory that the original object may have. This is different from a shallow copy, which only creates a new object that refers to the same memory as the original object.

Creating a copy constructor for a class is straightforward. The syntax for a copy constructor is as follows:

ClassName ( const ClassName & obj);

The copy constructor takes a reference to a constant object of the same class as an argument. The reference must be constant to avoid accidental modification of the original object.

Here’s an example of a copy constructor:

In this example, we have a class called Car with a private string member called make , another private string member called model , and a private integer member called year . We have defined a copy constructor for this class that takes a reference to a constant Car object as an argument.

Inside the copy constructor, we use the this keyword to refer to the current object and the dot operator to access its member variables. We then assign the values of the corresponding member variables of the passed object to the current object.

This is a simple example, but it demonstrates the basic syntax and usage of a copy constructor in C++. In the next section, we’ll explore the assignment operator and how it differs from the copy constructor.

In C++, the assignment operator is a special member function that assigns the value of one object to another object of the same class. This operator is denoted by the equal sign (=) and is invoked when this symbol is used to assign one object to another.

The assignment operator is used primarily for object assignment, which involves modifying the state of an existing object rather than creating a new one. This process can involve complex memory management capabilities, as the assignment operator must manage the allocation and deallocation of memory within the object.

Proper usage of the assignment operator is crucial for effective object manipulation, as it enables the copying of objects and their states. When used correctly, the assignment operator can facilitate memory management and efficient coding practices.

Having a solid understanding of the assignment operator in C++ is critical for proper object manipulation and memory management. Our next section will explore the key differences between the copy constructor and assignment operator, which are both essential for efficient programming.

While the copy constructor and assignment operator in C++ are both used for object copying, there are key differences between them. Understanding these differences is crucial for proper usage.

The first major difference is in the invocation of each function. The copy constructor is invoked when a new object is being initialized with an existing object, while the assignment operator is invoked when an object is already initialized and being assigned a new value.

Another significant distinction is in the return type of the functions. The copy constructor returns a new object of the same type as the original object being copied, while the assignment operator returns a reference to the object being assigned.

A third difference lies in the nature of the copying process itself. The copy constructor creates a new object as an exact duplicate of the original object, while the assignment operator modifies an existing object with the values of another object.

Finally, when it comes to memory management, the copy constructor and assignment operator also function differently. The copy constructor performs a deep copy, creating a new object with its own copy of dynamically allocated memory, while the assignment operator performs a shallow copy, where both objects share the same memory.

In summary, understanding the differences between the copy constructor and assignment operator is essential for proper object manipulation in C++. By keeping these distinctions in mind, we can efficiently and safely use these functions in our code.

When an object is copied in C++, there are two methods for handling the copying process: deep copy and shallow copy. These approaches have distinct implications for object initialization and memory management.

Deep Copy : When an object is deep copied, a new memory location is allocated for the copied object, and all of the data members and sub-objects are also copied. This means that changes made to the original object will not affect the copied object, and vice versa. In other words, the two objects are independent.

Shallow Copy : When an object is shallow copied, a new memory location is allocated for the copied object, but the data members and sub-objects are not copied. Instead, the copied object simply points to the same memory location as the original object. As a result, changes made to the original object will also affect the copied object, and vice versa. In other words, the two objects share the same data.

The copy constructor and assignment operator have different implications for deep copy and shallow copy:

Understanding the difference between deep copy and shallow copy is crucial for proper object initialization and memory management. The decision to use deep copy or shallow copy will depend on the specific needs of the program and the objects involved.

In C++, the copy constructor is a special member function that creates a new object as a copy of an existing object. It is invoked when an object is being initialized with an existing object.

The syntax for the copy constructor is as follows:

ClassName ( const ClassName& obj )

Here, ClassName is the name of the class, const ClassName& obj is a reference to the object being copied, and the constructor body initializes the new object based on the existing object.

Let’s look at an example to see how the copy constructor works in practice:

When using the copy constructor, it’s important to note that a shallow copy of the object is created if no special instructions are given. In other words, if the object contains pointers or other reference types, the copy will point to the same memory locations as the original object. To create a deep copy that copies all the data as well as any dynamic memory, it’s necessary to write a custom copy constructor or overload the assignment operator.

Now that we have discussed the copy constructor, let’s move on to the assignment operator. The syntax for the assignment operator is as follows:

class_name& operator=(const class_name& other_object)

The assignment operator is a member function of a class, just like the copy constructor. It is used to assign one object to another object of the same class. Let’s take a look at an example:

In the example above, we define the assignment operator function for the MyClass class. The function takes a constant reference to another object of the same class as a parameter. We first check if the object being assigned is not the same as the current object, to avoid self-assignment issues. We then copy the data from the other object to the current object, and finally, we return a reference to the current object.

Using the assignment operator is easy and intuitive. Suppose we have two objects of the MyClass class, obj1 and obj2. We can use the assignment operator to assign the value of obj2 to obj1 as follows:

obj1 = obj2;

This will copy the data from obj2 to obj1.

Knowing when to use the copy constructor in C++ is essential for efficient object copying. The copy constructor is typically used when we need to create a new object that is a copy of an existing object. This can occur in several scenarios, such as:

• Passing an object by value to a function
• Returning an object from a function
• Initializing an object with another object of the same class

It’s important to note that when using the copy constructor, a new object is created with its own memory and resources, which is known as a deep copy. This ensures that any changes made to the copied object do not affect the original object, avoiding any memory-related issues.

In summary, when we need to create a new object as a copy of an existing object, we should use the copy constructor in C++. This provides us with a deep copy of the object, which is vital for proper memory management and avoiding issues related to object copying.

Now that we have covered the basics of the assignment operator in C++, let’s discuss when it should be used. The assignment operator is primarily used when we want to assign the value of one object to another object of the same class. This is known as object assignment.

For example, let’s say we have two objects, object1 and object2, of the same class. We can use the assignment operator to transfer the value of object1 to object2, like this:

object2 = object1;

This will make the value of object2 identical to that of object1, effectively copying object1’s data into object2. Keep in mind that the objects must be of the same class for this to work properly.

The assignment operator is a useful tool for manipulating objects in C++. However, it should be used with caution. Improper use of the assignment operator can lead to memory leaks and other issues, so it’s important to understand its syntax and proper usage.

Now that we understand the basics of copy constructors and their differences with assignment operators, let’s take a closer look at an example that showcases how a copy constructor works in C++.

“A copy constructor is used to initialize an object from another object of the same type. It is called when an object is constructed based on another object of the same class.”

Consider the following code:

In the code above, we have defined a Person class with a default constructor, a custom constructor, and a copy constructor. We then create three instances of the Person class – john , mary , and emily , using different constructors.

The line Person emily = mary; initializes the emily object as a copy of the mary object, using the copy constructor. This means that emily now has the same values for name and age as mary .

The output of the code will be:

We can see that emily has been correctly initialized as a copy of mary , using the copy constructor.

Overall, the copy constructor is an essential part of C++ object initialization and is particularly useful when we need to make a copy of an existing object, such as when passing objects as function arguments or returning objects from functions.

In the next section, we will explore an example that showcases the usage and differences of the assignment operator in C++.

Now that we’ve seen an example of the copy constructor in action, let’s take a closer look at the assignment operator. As we mentioned earlier, the assignment operator is used to assign the value of one object to another object of the same class. The syntax for the assignment operator is similar to that of the copy constructor, but with a few key differences.

To illustrate the usage of the assignment operator, let’s consider a simple example class called Person:

// Person.h class Person { public: Person(); Person(const std::string& name, int age); ~Person(); std::string getName() const; int getAge() const; void setName(const std::string& name); void setAge(int age); void print(); Person operator=(const Person& other); private: std::string m_name; int m_age; };

In this class, we have a constructor, destructor, getter and setter functions for the name and age attributes, and a print function to display the name and age of a person. We also have defined an assignment operator, which takes an object of the same class as input and assigns its values to the current object:

// Person.cpp Person Person::operator=(const Person& other) { m_name = other.m_name; m_age = other.m_age; return *this; }

In this example, we’ve implemented a simple assignment operator that copies the name and age attributes of the passed object to the current object. Note that we’re returning a reference to the current object.

Let’s see how we can use the assignment operator:

// main.cpp #include “Person.h” #include <iostream> int main() { Person p1(“John”, 25); Person p2; p2 = p1; p1.print(); p2.print(); return 0; }

In this example, we create two Person objects, p1 and p2. We then assign the value of p1 to p2 using the assignment operator. Finally, we print the values of both objects to confirm that the assignment was successful.

This example demonstrates how to use the assignment operator to assign the values of one object to another object of the same class. Note that the syntax and usage of the assignment operator are different from those of the copy constructor.

By now, we’ve explored the differences between the copy constructor and assignment operator in C++, with specific examples illustrating their usage. Both of these functions are essential for object copying and assignment, and understanding their differences is crucial for effective programming. In the next section, we’ll discuss the distinction between shallow copy and deep copy, and how it related to object copying in C++.

As professional copywriting journalists, we understand the importance of constructors and assignment operators in C++. The copy constructor and assignment operator are used to copy and assign objects, respectively. Although they may seem similar, they serve different purposes, and understanding their differences is crucial for efficient programming.

In summary, the copy constructor creates a new object as a copy of an existing object, while the assignment operator assigns the value of one object to another object of the same class. The copy constructor is typically used when an object needs to be initialized as a copy of another object, while the assignment operator is commonly used when an object needs to be assigned the value of another object.

It is essential to understand the syntax and usage of the copy constructor and assignment operator to implement them correctly. When implementing the copy constructor, it is important to consider whether a deep or shallow copy is required. A deep copy creates a new object and copies all the data members of the existing object while a shallow copy copies only the address of the data members, resulting in two objects sharing the same memory.

Similarly, when implementing the assignment operator, it is important to consider memory management. A deep copy is generally required to ensure that the objects that are being assigned do not share the same memory.

In summary, understanding the differences between the copy constructor and assignment operator and their appropriate usage is essential for efficient object manipulation in C++. Always remember to consider memory management when implementing these member functions.

It is important to understand the distinction between the copy constructor and assignment operator in C++. While both are used for object copying, they serve different purposes. The copy constructor is used to initialize an object as a copy of an existing object. On the other hand, the assignment operator is used to assign the value of one object to another object of the same class.

One key difference between the two is in their invocation. The copy constructor is automatically invoked when a new object is being initialized with an existing object. The assignment operator, on the other hand, is manually invoked using the “=” operator to assign one object to another.

Another significant difference lies in their implementation. The copy constructor creates a new object and initializes it as an exact copy of an existing object. The assignment operator, on the other hand, does not create a new object but instead assigns the value of an existing object to another object of the same class.

Understanding the distinction between the copy constructor and assignment operator is necessary for proper object manipulation in C++. Knowing when to use each one is essential for effective programming and memory management.

In C++, constructors and assignment operators play integral roles in object initialization and memory management. It is essential to understand the difference between the copy constructor and assignment operator for efficient programming.

Although both the copy constructor and assignment operator are used in object copying, they differ in their usage and purpose:

The copy constructor is utilized when a new object is being initialized with an existing object, creating a new object as a copy of an existing object. On the other hand, the assignment operator is utilized when the value of one object is assigned to another object of the same class.

Let’s explore examples that highlight the differences between the copy constructor and assignment operator in C++ in more detail:

Consider a class named Car with private properties such as model, make, and year. Here’s an example of a copy constructor in C++, which initializes a new Car object as a copy of an existing Car object:

When the copy constructor is invoked in the above example, it creates a new Car object named myNewCar, which is a copy of the existing object myCar. The output shows that both cars have the same make, model, and year, confirming that the copy constructor has worked correctly.

Let’s now look at an example that demonstrates the usage of the assignment operator in C++. Consider the same Car class with private properties such as model, make, and year:

In the above example, the assignment operator is used to assign the value of myCar to myNewCar, replacing the original value of myNewCar. The output shows that myNewCar has been assigned the same make, model, and year as myCar.

By understanding the differences between the copy constructor and assignment operator, you can ensure efficient and safe programming in C++. Implementing these methods correctly can prevent errors and enable better memory management, leading to more effective object manipulation in your programs.

When dealing with object copying in C++, proper memory management is crucial. The way an object is copied can have a significant impact on the program’s memory usage and overall efficiency. There are two ways to handle object copying in C++: deep copy and shallow copy.

Deep copy involves copying all the members of an object, including dynamic memory allocations. This means that a completely new object is created, with its own separate memory space. Deep copying is useful for complex objects with dynamically allocated memory, where each object needs to have its own copy of the data.

Shallow copy , on the other hand, only copies the memory address of each object’s members. This means that two objects may share the same memory locations, making changes to one object affect the other. Shallow copying is useful for simple objects, where there is no dynamically allocated memory.

To ensure proper memory management and prevent memory leaks, it is essential to understand the implications of each approach and use them appropriately.

As we have learned, the copy constructor and assignment operator serve distinct purposes in C++ object initialization and assignment.

Understanding their differences is crucial for proper object copying and assignment. The copy constructor is used when an object needs to be initialized as a copy of another object, while the assignment operator is commonly used when an object needs to be assigned the value of another object.

Furthermore, knowing the difference between deep copy and shallow copy is essential for efficient memory management when dealing with object copying. Deep copy creates a new object with its own memory, while shallow copy shares memory with the original object, potentially leading to memory-related issues.

By implementing the copy constructor and assignment operator correctly and understanding their appropriate usage, we can ensure efficient and error-free programming in C++. Remember to always pay attention to memory management and choose the right method of object copying for your specific needs.

A: The copy constructor is used to create a new object as a copy of an existing object, while the assignment operator is used to assign the value of one object to another object of the same class.

A: A copy constructor is a special member function that is used to create a new object as a copy of an existing object. It is invoked when a new object is being initialized with an existing object.

A: An assignment operator is a special member function that is used to assign the value of one object to another object of the same class. It is invoked when the “=” operator is used to assign one object to another.

A: Although both the copy constructor and assignment operator are used for object copying, there are some key differences between them. Understanding these differences is essential for proper usage.

A: When an object is copied, there are two ways to handle the copying process: deep copy and shallow copy. Understanding the implications of each approach is vital for correct object initialization.

A: The syntax and usage of a copy constructor in C++ involve specific rules and conventions. Knowing how to implement and use the copy constructor correctly is essential for proper object copying.

A: The syntax and usage of an assignment operator in C++ also follow specific rules and conventions. Understanding how to implement and use the assignment operator properly is crucial for object assignment.

A: The copy constructor is typically used when an object needs to be initialized as a copy of another object. Knowing when to use the copy constructor is important for efficient and safe programming.

A: The assignment operator is commonly used when an object needs to be assigned the value of another object. Understanding when to use the assignment operator is crucial for proper object manipulation.

A: To illustrate the usage and differences between the copy constructor and assignment operator, let’s look at an example that showcases the copy constructor in C++.

A: Continuing from the previous example, let’s explore an example that demonstrates the usage and differences of the assignment operator in C++.

A: By now, you should have a solid understanding of the copy constructor and assignment operator in C++. Knowing their purpose and differences is essential for effective object manipulation.

A: The distinction between the copy constructor and assignment operator lies in their usage and purpose. Understanding this distinction is crucial for correctly managing object copying and assignment in C++.

A: To further clarify the differences between the copy constructor and assignment operator, let’s explore some specific examples that highlight these distinctions.

A: Proper memory management is crucial when dealing with object copying in C++. Understanding the difference between deep copy and shallow copy is essential for avoiding memory-related issues.

Deepak Vishwakarma

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• C++ Unordered_Mutimap
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• Stein's Algorithm to find GCD in C++
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• Xor_eq in C++
• C++ MCQ Part 2
• Interview Question

C++ STL Bitset

• bitset all() function
• bitset any() function
• bitset count() function
• bitset flip() function
• bitset none() function
• bitset operator[]
• bitset reset() function
• bitset set() function
• bitset size() function
• bitset test() function
• bitset to_string() function
• bitset to_ullong() function
• bitset to_ulong() function

C++ STL Deque

• Deque assign() function
• Deque emplace() function
• Deque emplace_back() function
• Deque emplace_front() function
• Deque insert() function
• Deque push_back() function
• Deque push_front() function
• Deque pop_back() function
• Deque pop_front() function
• Deque swap() function
• Deque clear() function
• Deque empty() function
• Deque erase() function
• Deque max_size() function
• Deque resize() function
• Deque shrink_to_fit() function
• Deque size() function
• Deque at() function
• Deque operator[]() function
• Deque operator=() function
• Deque back() function
• Deque begin() function
• Deque cbegin() function
• Deque end() function
• Deque cend() function
• Deque rbegin() function
• Deque crbegin() function
• Deque rend() function
• Deque crend() function

C++ STL List

• List insert() function
• List push_back() function
• List push_front() function
• List pop_back() function
• List pop_front() function
• List empty() function
• List size() function
• List max_size() function
• List front() function
• List back() function
• List swap() function
• List reverse() function
• List sort() function
• List merge() function
• List splice() function
• List unique() function
• List resize() function
• List assign() function
• List emplace() function
• List emplace_back() function
• List emplace_front() function

C++ STL Map

• map at() function
• map begin() function
• map cbegin() function
• map cend() function
• map crbegin() function
• map crend() function
• map empty() function
• map end() function
• map max_size() function
• map operator[]
• map rbegin() function
• map rend() function
• map size() function
• map clear() function
• map emplace() function
• map emplace_hint() function
• map erase() function
• map find() function
• map insert() function
• map operator=()
• map swap() function

C++ STL Math

• math cos() function
• math sin() function
• math tan() function
• math acos() function
• math asin() function
• math atan() function
• math atan2() function
• math cosh() function
• math sinh() function
• math tanh() function
• math acosh() function
• math asinh() function
• math atanh() function
• math exp() function
• math frexp() function
• math Idexp() function
• math log() function
• math log10() function
• math modf() function
• math exp2() function
• math expm1() function
• math log1p() function
• math log2() function
• math logb() function
• math scalbn() function
• math scalbln() function
• math ilogb() function
• math copysign() function
• math nextafter() function
• math nexttoward() function
• math fdim() function
• math fmax() function
• math fmin() function
• math pow() function
• math sqrt() function
• math cbrt() function
• math hypot() function
• math ceil() function
• math floor() function
• math round() function
• math lround() function
• math llround() function
• math fmod() function
• math trunc() function
• math rint() function
• math lrint() function
• math llrint() function
• math nearbyint() function
• math remainder() function
• math remquo() function
• math fabs() function
• math abs() function
• math fma() function
• math fpclassify() function
• math isfinite() function
• math isinf() function
• math isnan() function
• math isnormal() function
• math signbit() function
• math isgreater() function
• math isgreaterequal() function
• math less() function
• math islessequal() function
• math islessgreater() function
• math isunordered() function
• math erf() function
• math erfc() function
• math tgamma() function
• math lgamma() function

C++ STL priority_queue

• C++ priority_queue
• priority_queue emplace() function
• priority_queue empty() function
• priority_queue pop() function
• priority_queue push() function
• priority_queue size() function
• priority_queue swap() function
• priority_queue top() function

C++ STL Stack

• stack emplace() function
• stack empty() function
• stack pop() function
• stack push() function
• stack size() function
• stack top() function

C++ STL Queue

• queue back() function
• queue emplace() function
• queue empty() function
• queue front() function
• queue pop() function
• queue push() function
• queue size() function

C++ STL Multiset

• C++ multiset
• multiset constructor
• multiset destructor
• multiset begin() function
• multiset end() function
• multiset operator=
• multiset rbegin() function
• multiset rend() function
• multiset cbegin() function
• multiset cend() function
• multiset max_size() function
• multiset size() function
• multiset crbegin() function
• multiset crend() function
• multiset empty() function
• multiset insert() function
• multiset clear() function
• multiset emplace() function
• multiset erase() function
• multiset swap() function
• multiset emplace_hint() function
• multiset find() function
• multiset key_comp() function
• multiset value_comp() function
• multiset count() function
• multiset equal_range() function
• multiset lower_bound() function
• multiset upper_bound() function
• multiset get_allocator() function
• multiset operator==
• multiset operator!=
• multiset operator<
• multiset operator<=
• multiset operator>
• multiset operator>=

C++ STL Multimap

• multimap crbegin() function
• multimap crend() function
• multimap begin() function
• multimap cbegin() function
• multimap cend() function
• multimap end() function
• multimap rbegin() function
• multimap rend() function
• multimap clear() function
• multimap emplace() function
• multimap empty() function
• multimap erase() function
• multimap insert() function
• multimap swap() function
• multimap equal_range() function
• multimap operator==
• multimap operator!=
• multimap operator<
• multimap operator<=
• multimap operator>
• multimap operator>=

C++ STL Set

• set constructor
• set destructor
• set operator=() function
• set begin() function
• set cbegin() function
• set end() function
• set cend() function
• set rbegin() function
• set rend() function
• set crbegin() function
• set crend() function
• set empty() function
• set Size() function
• set max_size() function
• set insert() function
• set erase() function
• set Swap() function
• set clear() function
• set emplace() function
• set emplace_hint() function
• set key_comp() function
• set value_comp() function
• set find() function
• set count() function
• set lower_bound() function
• set upper_bound() function
• set equal_range() function
• set get_allocator() function
• set operator==
• set operator!=
• set operator<
• set operator<=
• set operator>
• set operator>=
• set swap() function

C++ STD Strings

• string compare() function
• string length() function
• string swap() function
• string size() function
• string resize() function
• string replace() function
• string append() function
• string at() function
• string find() function
• string find_first_of() function
• string find_first_not_of() function
• string find_last_of() function
• string find_last_not_of() function
• string insert() function
• string max_size() function
• string push_back() function
• string pop_back() function
• sstring assign() function
• string copy() function
• string back() function
• string begin() function
• string capacity() function
• string cbegin() function
• string cend() function
• string clear() function
• string crbegin() function
• string data() function
• string empty() function
• string erase() function
• string front() function
• string operator+=()
• string operator=()
• string operator[]()
• string rfind() function
• string end() function
• string rend() function
• string shrink_to_fit() function
• string c_str() function
• string crend() function
• string rbegin() function
• string reserve() function

C++ STL Vector

• Vector at() function
• Vector back() function
• Vector front() function
• Vector swap() function
• Vector push_back() function
• Vector pop_back() function
• Vector empty() function
• Vector insert() function
• Vector erase() function
• Vector resize() function
• Vector clear() function
• Vector size() function
• Vector capacity() function
• Vector assign() function
• Vector operator=() function
• Vector operator[]() function
• Vector end() function
• Vector emplace() function
• Vector emplace_back() function
• Vector rend() function
• Vector rbegin() function
• Vector begin() function
• Vector max_size() function
• Vector cend() function
• Vector cbegin() function
• Vector crbegin() function
• Vector crend() function
• Vector data() function
• Vector shrink_to_fit() function

The object-oriented programming idea is supported by the general-purpose, middle-level, case-sensitive, platform agnostic computer language C++. Bjarne Stroustrup developed the C++ programming language in 1979 at Bell Laboratories. Since C++ is a platform-independent programming language, it may be used on a wide range of operating systems, including Windows, Mac OS, and different UNIX versions. Assignment operators are used to assign values to variables from the aforementioned groups. Let's first study a little bit about constructors before moving on to copy constructors. When an object is formed, a specific method called a constructor-which has the same name as the class name with the parentheses "()"-is automatically called. Initializing the variables of a freshly generated object is done using the constructor. A copy constructor is a form of constructor that uses an already-created object from the same class to initialize a new object. Let's now go over the specifics of the notion and contrast and compare the features of the assignment operator and copy constructor. The assignment operator is used to give a variable a value. The assignment operator has a variable name as its left operand and a value to that variable as its right operand. A compilation error will be triggered if neither operand's datatype matches the other. Assignment operators come in various forms. : = operator Only the value is given to the variable. For instance, if "a=10," variable "a" will be given the value of 10. The += operator first multiplies the variable's current value by the value on the right side before assigning the new value. The operator "-=" first subtracts the variable's current value from the value on the right side before appending the new value. In order to assign a new value to a variable, the *= operator first multiplies the variable's current value by the value on the right side. The operator /= first divides the variable's current value by the value on the right side before assigning the new value to the variable. Below is an illustration of an assignment operator. The assignment operator is being used in this case to give values to several variables. The two variables "a" and "b" were used in the example above, and we first set the value of "a" to 5 using the assignment operator "=". And we've given variable b the value of the a variable. The output from the aforementioned code is shown below. Programmers frequently need to do this in order to duplicate an object without affecting the original. The copy constructor is used in these circumstances. The copy constructor produces an object by initializing it with a different object of the same class that has already been constructed. The copy constructor comes in two varieties. The default copy constructor is created by the C++ compiler when the copy constructor is not declared, and it copies all member variables exactly as they are. User-Defined Copy Constructor: This term refers to a copy constructor that has been defined by the user. The syntax for Copy Constructor is - All of these C++ concepts' primary functions are to assign values, but the key distinction between them is that while the copy constructor produces a new object and assigns the value, the assignment operator assigns the value to the data member of the same object rather than to a new object. The key distinctions between assignment operator and copy constructor are shown in the following table. Copy constructor Assignment operator An example of an overloaded constructor is the copy constructor. A new object is initialized by an existing object of the same type using the copy constructor. An operator that assigns a value to objects or data members is known as an assignment operator. It transfers an object's value from one produced object to another. When an old object is used to initialize a new one, as well as when the object is supplied to a function as a non-reference parameter, the copy constructor is called. When an old object's value is transferred to a new object, the assignment operator is used. The newly invoked object will share distinct memory addresses with the previously generated object. The first object and the second object, to whom the first object's value is assigned, share the same memory addresses. Latest Courses We provides tutorials and interview questions of all technology like java tutorial, android, java frameworks Contact info G-13, 2nd Floor, Sec-3, Noida, UP, 201301, India [email protected] . Interview Questions Online compiler. This browser is no longer supported. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. C++ At Work Copy Constructors, Assignment Operators, and More Paul DiLascia Code download available at: CAtWork0509.exe (276 KB) Browse the Code Online Q I have a simple C++ problem. I want my copy constructor and assignment operator to do the same thing. Can you tell me the best way to accomplish this? A At first glance this seems like a simple question with a simple answer: just write a copy constructor that calls operator=. Or, alternatively, write a common copy method and call it from both your copy constructor and operator=, like so: This code works fine for many classes, but there's more here than meets the eye. In particular, what happens if your class contains instances of other classes as members? To find out, I wrote the test program in Figure 1 . It has a main class, CMainClass, which contains an instance of another class, CMember. Both classes have a copy constructor and assignment operator, with the copy constructor for CMainClass calling operator= as in the first snippet. The code is sprinkled with printf statements to show which methods are called when. To exercise the constructors, cctest first creates an instance of CMainClass using the default ctor, then creates another instance using the copy constructor: Figure 1 Copy Constructors and Assignment Operators If you compile and run cctest, you'll see the following printf messages when cctest constructs obj2: The member object m_obj got initialized twice! First by the default constructor, and again via assignment. Hey, what's going on? In C++, assignment and copy construction are different because the copy constructor initializes uninitialized memory, whereas assignment starts with an existing initialized object. If your class contains instances of other classes as data members, the copy constructor must first construct these data members before it calls operator=. The result is that these members get initialized twice, as cctest shows. Got it? It's the same thing that happens with the default constructor when you initialize members using assignment instead of initializers. For example: As opposed to: Using assignment, m_obj is initialized twice; with the initializer syntax, only once. So, what's the solution to avoid extra initializations during copy construction? While it goes against your instinct to reuse code, this is one situation where it's best to implement your copy constructor and assignment operator separately, even if they do the same thing. Calling operator= from your copy constructor will certainly work, but it's not the most efficient implementation. My observation about initializers suggests a better way: Now the main copy ctor calls the member object's copy ctor using an initializer, and m_obj is initialized just once by its copy ctor. In general, copy ctors should invoke the copy ctors of their members. Likewise for assignment. And, I may as well add, the same goes for base classes: your derived copy ctor and assignment operators should invoke the corresponding base class methods. Of course, there are always times when you may want to do something different because you know how your code works—but what I've described are the general rules, which are to be broken only when you have a compelling reason. If you have common tasks to perform after the basic objects have been initialized, you can put them in a common initialization method and call it from your constructors and operator=. Q Can you tell me how to call a Visual C++® class from C#, and what syntax I need to use for this? Sunil Peddi Q I have an application that is written in both C# (the GUI) and in classic C++ (some business logic). Now I need to call from a DLL written in C++ a function (or a method) in a DLL written in Visual C++ .NET. This one calls another DLL written in C#. The Visual C++ .NET DLL acts like a proxy. Is this possible? I was able to use LoadLibrary to call a function present in the Visual C++ .NET DLL, and I can receive a return value, but when I try to pass some parameters to the function in the Visual C++ .NET DLL, I get the following error: How can I resolve this problem? Giuseppe Dattilo A I get a lot of questions about interoperability between the Microsoft® .NET Framework and native C++, so I don't mind revisiting this well-covered topic yet again. There are two directions you can go: calling the Framework from C++ or calling C++ from the Framework. I won't go into COM interop here as that's a separate issue best saved for another day. Let's start with the easiest one first: calling the Framework from C++. The simplest and easiest way to call the Framework from your C++ program is to use the Managed Extensions. These Microsoft-specific C++ language extensions are designed to make calling the Framework as easy as including a couple of files and then using the classes as if they were written in C++. Here's a very simple C++ program that calls the Framework's Console class: To use the Managed Extensions, all you need to do is import <mscorlib.dll> and whatever .NET assemblies contain the classes you plan to use. Don't forget to compile with /clr: Your C++ code can use managed classes more or less as if they were ordinary C++ classes. For example, you can create Framework objects with operator new, and access them using C++ pointer syntax, as shown in the following: Here, the String s is declared as pointer-to-String because String::Format returns a new String object. The "Hello, world" and date/time programs seem childishly simple—and they are—but just remember that however complex your program is, however many .NET assemblies and classes you use, the basic idea is the same: use <mscorlib.dll> and whatever other assemblies you need, then create managed objects with new, and use pointer syntax to access them. So much for calling the Framework from C++. What about going the other way, calling C++ from the Framework? Here the road forks into two options, depending on whether you want to call extern C functions or C++ class member functions. Again, I'll take the simpler case first: calling C functions from .NET. The easiest thing to do here is use P/Invoke. With P/Invoke, you declare the external functions as static methods of a class, using the DllImport attribute to specify that the function lives in an external DLL. In C# it looks like this: This tells the compiler that MessageBox is a function in user32.dll that takes an IntPtr (HWND), two Strings, and an int. You can then call it from your C# program like so: Of course, you don't need P/Invoke for MessageBox since the .NET Framework already has a MessageBox class, but there are plenty of API functions that aren't supported directly by the Framework, and then you need P/Invoke. And, of course, you can use P/Invoke to call C functions in your own DLLs. I've used C# in the example, but P/Invoke works with any .NET-based language like Visual Basic® .NET or JScript®.NET. The names are the same, only the syntax is different. Note that I used IntPtr to declare the HWND. I could have got away with int, but you should always use IntPtr for any kind of handle such as HWND, HANDLE, or HDC. IntPtr will default to 32 or 64 bits depending on the platform, so you never have to worry about the size of the handle. DllImport has various modifiers you can use to specify details about the imported function. In this example, CharSet=CharSet.Auto tells the Framework to pass Strings as Unicode or Ansi, depending on the target operating system. Another little-known modifier you can use is CallingConvention. Recall that in C, there are different calling conventions, which are the rules that specify how the compiler should pass arguments and return values from one function to another across the stack. The default CallingConvention for DllImport is CallingConvention.Winapi. This is actually a pseudo-convention that uses the default convention for the target platform; for example, StdCall (in which the callee cleans the stack) on Windows® platforms and CDecl (in which the caller cleans the stack) on Windows CE .NET. CDecl is also used with varargs functions like printf. The calling convention is where Giuseppe ran into trouble. C++ uses yet a third calling convention: thiscall. With this convention, the compiler uses the hardware register ECX to pass the "this" pointer to class member functions that don't have variable arguments. Without knowing the exact details of Giuseppe's program, it sounds from the error message that he's trying to call a C++ member function that expects thiscall from a C# program that's using StdCall—oops! Aside from calling conventions, another interoperability issue when calling C++ methods from the Framework is linkage: C and C++ use different forms of linkage because C++ requires name-mangling to support function overloading. That's why you have to use extern "C" when you declare C functions in C++ programs: so the compiler won't mangle the name. In Windows, the entire windows.h file (now winuser.h) is enclosed in extern "C" brackets. While there may be a way to call C++ member functions in a DLL directly using P/Invoke and DllImport with the exact mangled names and CallingConvention=ThisCall, it's not something to attempt if you're in your right mind. The proper way to call C++ classes from managed code—option number two—is to wrap your C++ classes in managed wrappers. Wrapping can be tedious if you have lots of classes, but it's really the only way to go. Say you have a C++ class CWidget and you want to wrap it so .NET clients can use it. The basic formula looks something like this: The pattern is the same for any class. You write a managed (__gc) class that holds a pointer to the native class, you write a constructor and destructor that allocate and destroy the instance, and you write wrapper methods that call the corresponding native C++ member functions. You don't have to wrap all the member functions, only the ones you want to expose to the managed world. Figure 2 shows a simple but concrete example in full detail. CPerson is a class that holds the name of a person, with member functions GetName and SetName to change the name. Figure 3 shows the managed wrapper for CPerson. In the example, I converted Get/SetName to a property, so .NET-based programmers can use the property syntax. In C#, using it looks like this: Figure 3 Managed Person Class Figure 2 Native CPerson Class Using properties is purely a matter of style; I could equally well have exposed two methods, GetName and SetName, as in the native class. But properties feel more like .NET. The wrapper class is an assembly like any other, but one that links with the native DLL. This is one of the cool benefits of the Managed Extensions: You can link directly with native C/C++ code. If you download and compile the source for my CPerson example, you'll see that the makefile generates two separate DLLs: person.dll implements a normal native DLL and mperson.dll is the managed assembly that wraps it. There are also two test programs: testcpp.exe, a native C++ program that calls the native person.dll and testcs.exe, which is written in C# and calls the managed wrapper mperson.dll (which in turn calls the native person.dll). Figure 4** Interop Highway ** I've used a very simple example to highlight the fact that there are fundamentally only a few main highways across the border between the managed and native worlds (see Figure 4 ). If your C++ classes are at all complex, the biggest interop problem you'll encounter is converting parameters between native and managed types, a process called marshaling. The Managed Extensions do an admirable job of making this as painless as possible (for example, automatically converting primitive types and Strings), but there are times where you have to know something about what you're doing. For example, you can't pass the address of a managed object or subobject to a native function without pinning it first. That's because managed objects live in the managed heap, which the garbage collector is free to rearrange. If the garbage collector moves an object, it can update all the managed references to that object—but it knows nothing of raw native pointers that live outside the managed world. That's what __pin is for; it tells the garbage collector: don't move this object. For strings, the Framework has a special function PtrToStringChars that returns a pinned pointer to the native characters. (Incidentally, for those curious-minded souls, PtrToStringChars is the only function as of this date defined in <vcclr.h>. Figure 5 shows the code.) I used PtrToStringChars in MPerson to set the Name (see Figure 3 ). Figure 5 PtrToStringChars Pinning isn't the only interop problem you'll encounter. Other problems arise if you have to deal with arrays, references, structs, and callbacks, or access a subobject within an object. This is where some of the more advanced techniques come in, such as StructLayout, boxing, __value types, and so on. You also need special code to handle exceptions (native or managed) and callbacks/delegates. But don't let these interop details obscure the big picture. First decide which way you're calling (from managed to native or the other way around), and if you're calling from managed to native, whether to use P/Invoke or a wrapper. In Visual Studio® 2005 (which some of you may already have as beta bits), the Managed Extensions have been renamed and upgraded to something called C++/CLI. Think of the C++/CLI as Managed Extensions Version 2, or What the Managed Extensions Should Have Been. The changes are mostly a matter of syntax, though there are some important semantic changes, too. In general C++/CLI is designed to highlight rather than blur the distinction between managed and native objects. Using pointer syntax for managed objects was a clever and elegant idea, but in the end perhaps a little too clever because it obscures important differences between managed and native objects. C++/CLI introduces the key notion of handles for managed objects, so instead of using C pointer syntax for managed objects, the CLI uses ^ (hat): As you no doubt noticed, there's also a gcnew operator to clarify when you're allocating objects on the managed heap as opposed to the native one. This has the added benefit that gcnew doesn't collide with C++ new, which can be overloaded or even redefined as a macro. C++/CLI has many other cool features designed to make interoperability as straightforward and intuitive as possible. Send your questions and comments for Paul to   [email protected] . Paul DiLascia is a freelance software consultant and Web/UI designer-at-large. He is the author of Windows ++: Writing Reusable Windows Code in C ++ (Addison-Wesley, 1992). In his spare time, Paul develops PixieLib, an MFC class library available from his Web site, www.dilascia.com . Additional resources Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand OverflowAI GenAI features for Teams OverflowAPI Train & fine-tune LLMs Labs The future of collective knowledge sharing About the company Visit the blog Collectives™ on Stack Overflow Find centralized, trusted content and collaborate around the technologies you use most. Q&A for work Connect and share knowledge within a single location that is structured and easy to search. Get early access and see previews of new features. Does the assignment operator call copy constructor? Here inside main(), test c=a calls the copy constructor and allocates memory for the integer. No problem with that, both c.p and a.p point to different memory locations. But the line b=a causes b.p and a.p to point to the same memory location. I have created my own copy constructor, b.p and a.p should have pointed to different memory locations. What's going on here? Edit: To be precise, my question is what's the difference between implicitly-defined copy constructor and implicitly-defined copy assignment operator? Does this answer your question? What is The Rule of Three? –  Karsten Koop Commented Mar 16, 2020 at 10:55 4 Assignment a=b does not invoke the the copy-ctor. You will need to overload operator= for that. –  Lukas-T Commented Mar 16, 2020 at 10:56 memory leaks in p=new int(a); you must delete OLD p if it has a valid memory –  Landstalker Commented Mar 16, 2020 at 10:56 What if test a; a.show(); ? –  Jose Commented Mar 16, 2020 at 10:57 The value of the original int is not copied into the copy. –  Surt Commented Mar 16, 2020 at 10:57 5 Answers 5 Here also bit by bit copy is done (a.p and b.p pointing to same location), it does not invoke copy constructor because constructor is called when b in defined (default constructor).so you have to overload = operator Add this to your class test and you need to check the memory is allocated or not by new because new can fail to allocate requested memory. But here the copy constructor is called You do not want to pass src by value. this->p=src.p; would make b.p point to the same memory as a.p and that will crash when both want to delete it in the destructor, it also creates a memory leak for a.p as you are overwriting the pointer. Do you mean *this->p=*src.p; ? –  mch Commented Mar 16, 2020 at 11:10 @mch sorry for the mistake i did not note it , i would corrected it.Thanks –  srilakshmikanthanp Commented Mar 16, 2020 at 11:27 If you really want to use an *int, I'd use smart pointers, to simplify the resource ownership: however, it does not make too much sense to use a pointer or smart pointers (obfuscated code) considering that the lifespan of the int is the same than the object itself (so you don't have to dynamically allocate it): 1 This will create a memory leak for this->p . –  mch Commented Mar 16, 2020 at 11:11 you will do delete p in new instance destructor –  Landstalker Commented Mar 16, 2020 at 11:12 operator= is not for new instances. Both instances are fully constructed, so both have a valid pointer p and you overwrite the one from the left side. It has nothing to do with the destructor, the destructor cannot call delete on an overwritten pointer. –  mch Commented Mar 16, 2020 at 11:13 @mch ok, I thought it was only for new instances, thanks for the remark. (Edited) –  Landstalker Commented Mar 16, 2020 at 11:24 1 Firstly, you don't need if (NULL != this->p) : if p is null, delete p safely does nothing. Secondly, why this->p ? Simply p is enough. Thirdly, it's nullptr these days, not NULL . In summary: delete p; p = new etc. –  TonyK Commented Mar 16, 2020 at 11:56 I dont know why, but if I: instead of : a.p and b.p point to different addresses 1 If you don't know why it works it's no answer, is it? –  Lukas-T Commented Mar 17, 2020 at 6:45 @churill you are correct, and probably I need to learn more about "=", but, the person who made this question might be in hurry, and I do not think that declare b at the time of its initialisation it's that much of a difference, it might be good enough for the "questioner", and later the "questioner" might search the reason the code in my answer works of its own –  platinoob_ Commented Mar 17, 2020 at 8:01 You need to define operator=. The copy constructor won't be called for an already-constructed object. 2 This will create a memory leak for this->p . You can pass t as const test & . –  mch Commented Mar 16, 2020 at 11:12 Your Answer Reminder: Answers generated by artificial intelligence tools are not allowed on Stack Overflow. 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Count squares in my pi approximation Analytic continuation gives a covering space (and not just a local homeomorphism) How would you say "must" as in "Pet rabbits must be constantly looking for a way to escape."? 232 IMAGES Difference between copy constructor and assignment operator in C++ (OOP tutorial for beginners) Difference between Copy Constructor and Assignment Operator,Copy Difference Between Copy Constructor And Assignment Operator In C++ #183 Automatics, Copy Constructor, and Assignment Operator Difference between copy constructor and assignment operator in c++ What is the Difference Between Copy Constructor and Assignment Operator VIDEO Copy Constructor in C++ in Hindi (Lec-23) C# FAQ#160 Difference between constructor and property copy constructor in C++ Difference between constructor and method in Java 08_C++ Programming Implement copy constructor program of C++ language #coding#education #programming #cpp COMMENTS What's the difference between assignment operator and copy constructor? 6. the difference between a copy constructor and an assignment constructor is: In case of an assignment constructor it will not create any object means it apply on already created objects (<o1>=<o2>). And the basic functionalities in both are same, they will copy the data from o2 to o1 member-by-member. Copy Constructor vs Assignment Operator in C++ But, there are some basic differences between them: Copy constructor. Assignment operator. It is called when a new object is created from an existing object, as a copy of the existing object. This operator is called when an already initialized object is assigned a new value from another existing object. It creates a separate memory block for ... Copy constructors and copy assignment operators (C++) Use an assignment operator operator= that returns a reference to the class type and takes one parameter that's passed by const reference—for example ClassName& operator=(const ClassName& x);. Use the copy constructor. If you don't declare a copy constructor, the compiler generates a member-wise copy constructor for you. Difference Between Copy Constructor and Assignment Operator in C++ Conclusion. The difference between a copy constructor and an assignment operator is that a copy constructor helps to create a copy of an already existing object without altering the original value of the created object, whereas an assignment operator helps to assign a new value to a data member or an object in the program. Difference Between Copy Constructor and Assignment Operator in C++ Copy constructor and assignment operator, are the two ways to initialize one object using another object. The fundamental difference between the copy constructor and assignment operator is that the copy constructor allocates separate memory to both the objects, i.e. the newly created target object and the source object. The assignment operator allocates the same memory location to the newly ... Copy Constructor in C++ Copy constructor and Assignment operator are similar as they are both used to initialize one object using another object. But, there are some basic differences between them: Copy constructor Assignment operator It is called when a new object is created from an existing object, as a copy of the existing objectThis operator is called when an already Copy constructor vs assignment operator in C++ The Copy constructor and the assignment operators are used to initializing one object to another object. The main difference between them is that the copy constructor creates a separate memory block for the new object. But the assignment operator does not make new memory space. It uses the reference variable to point to the previous memory block. What's the difference between assignment operator and copy constructor The Copy constructor and the assignment operators are used to initialize one object to another object. The main difference between them is that the copy constructor creates a separate memory block for the new object. But the assignment operator does not make new memory space. It uses reference variable to point to the previous memory block. Copy constructors A copy constructor is a constructor which can be called with an argument of the same class type and copies the content of the argument without mutating the argument. ... generation of the implicitly-defined copy constructor is deprecated if T has a user-defined destructor or user-defined copy assignment operator. (since C++11) Copy constructors, assignment operators, Here's where the difference between exception handling and exception safety is important: we haven't prevented an exception from occurring; indeed, ... in either T's copy constructor or assignment operator throwing, you are politely required to provide a swap() overload for your type that does not Copy Constructors and Assignment Operators The difference between the two is that the copy constructor of the target is invoked when the source object is passed in at the time the target is constructed, such as in line 2. The assignment operator is invoked when the target object already exists, such as on line 4. What is the Difference Between Copy Constructor and Assignment Operator The difference between copy constructor and assignment operator is that copy constructor is a type of constructor that helps to create a copy of an already existing object without affecting the values of the original object while assignment operator is an operator that helps to assign a new value to a variable in the program. Reference: 1. Copy assignment operator Triviality of eligible copy assignment operators determines whether the class is a trivially copyable type. [] NoteIf both copy and move assignment operators are provided, overload resolution selects the move assignment if the argument is an rvalue (either a prvalue such as a nameless temporary or an xvalue such as the result of std::move), and selects the copy assignment if the argument is an ... 21.12 The difference between the copy constructor and the copy assignment operator causes a lot of confusion for new programmers, but it's really not all that difficult. Summarizing: If a new object has to be created before the copying can occur, the copy constructor is used (note: this includes passing or returning objects by value). Difference Between Copy Constructor and Assignment Operator in C++ In C++, constructors and assignment operators play critical roles in object initialization and memory management. It is crucial to understand the difference between the copy constructor and assignment operator for efficient programming.. The C++ language provides special member functions for creating and manipulating objects. Difference between Copy Constructor and Assignment Operator? The copy constructor is used when you create a new object, specifying an object to copy, so. MyClass b(a); ( MyClass b = a; is the same) Uses the copy constructor. The assignment operator changes the value of an existing object, so in your case: MyClass b; Creates b and. b = a; uses the assignment operator, which you haven't defined. The distinction between the C++ copy constructor and assignment operator The distinction between the C++ copy constructor and assignment operator. The object-oriented programming idea is supported by the general-purpose, middle-level, case-sensitive, platform agnostic computer language C++. Bjarne Stroustrup developed the C++ programming language in 1979 at Bell Laboratories. Since C++ is a platform-independent ... C++ at Work: Copy Constructors, Assignment Operators, and More Both classes have a copy constructor and assignment operator, with the copy constructor for CMainClass calling operator= as in the first snippet. The code is sprinkled with printf statements to show which methods are called when. ... but in the end perhaps a little too clever because it obscures important differences between managed and native ... c++ What is the difference between the functionality of a copy constructor and an Assignment operator. Difference is that copy ctor constructs new object with a copy of existing one, assignment operator overrides fully constructed object with a copy. For example if you have a raw pointer to dynamically allocated memory in your class - copy ctor ... c++ This is known as Copy initialization.. Copy Initialization is defined as: T t2 = t1; Depending on type of t1 two scenarios are possible: . If t1 is NOT of the type T:. It tries to convert t1 to type T by using a implicit conversion sequence and ; then copies the created object in to t2 by calling the copy constructor.; If t1 is of the type T:. It copies t1 in to t2 by calling the copy constructor. Does the assignment operator call copy constructor? Here also bit by bit copy is done (a.p and b.p pointing to same location), it does not invoke copy constructor because constructor is called when b in defined (default constructor).so you have to overload = operator. test &operator =(const test &src) {. *this->p=*src.p; //copy value not address. return *this; essay homework paper phd project resume review speech thesis