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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

cppreference.com

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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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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21.12 — Overloading the assignment operator

The copy assignment operator (operator=) is used to copy values from one object to another already existing object .

Related content

As of C++11, C++ also supports “Move assignment”. We discuss move assignment in lesson 22.3 -- Move constructors and move assignment .

Copy assignment vs Copy constructor

The purpose of the copy constructor and the copy assignment operator are almost equivalent -- both copy one object to another. However, the copy constructor initializes new objects, whereas the assignment operator replaces the contents of existing objects.

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).
• If a new object does not have to be created before the copying can occur, the assignment operator is used.

Overloading the assignment operator

Overloading the copy assignment operator (operator=) is fairly straightforward, with one specific caveat that we’ll get to. The copy assignment operator must be overloaded as a member function.

This prints:

This should all be pretty straightforward by now. Our overloaded operator= returns *this, so that we can chain multiple assignments together:

Issues due to self-assignment

Here’s where things start to get a little more interesting. C++ allows self-assignment:

This will call f1.operator=(f1), and under the simplistic implementation above, all of the members will be assigned to themselves. In this particular example, the self-assignment causes each member to be assigned to itself, which has no overall impact, other than wasting time. In most cases, a self-assignment doesn’t need to do anything at all!

However, in cases where an assignment operator needs to dynamically assign memory, self-assignment can actually be dangerous:

First, run the program as it is. You’ll see that the program prints “Alex” as it should.

Now run the following program:

You’ll probably get garbage output. What happened?

Consider what happens in the overloaded operator= when the implicit object AND the passed in parameter (str) are both variable alex. In this case, m_data is the same as str.m_data. The first thing that happens is that the function checks to see if the implicit object already has a string. If so, it needs to delete it, so we don’t end up with a memory leak. In this case, m_data is allocated, so the function deletes m_data. But because str is the same as *this, the string that we wanted to copy has been deleted and m_data (and str.m_data) are dangling.

Later on, we allocate new memory to m_data (and str.m_data). So when we subsequently copy the data from str.m_data into m_data, we’re copying garbage, because str.m_data was never initialized.

Detecting and handling self-assignment

Fortunately, we can detect when self-assignment occurs. Here’s an updated implementation of our overloaded operator= for the MyString class:

By checking if the address of our implicit object is the same as the address of the object being passed in as a parameter, we can have our assignment operator just return immediately without doing any other work.

Because this is just a pointer comparison, it should be fast, and does not require operator== to be overloaded.

When not to handle self-assignment

Typically the self-assignment check is skipped for copy constructors. Because the object being copy constructed is newly created, the only case where the newly created object can be equal to the object being copied is when you try to initialize a newly defined object with itself:

In such cases, your compiler should warn you that c is an uninitialized variable.

Second, the self-assignment check may be omitted in classes that can naturally handle self-assignment. Consider this Fraction class assignment operator that has a self-assignment guard:

If the self-assignment guard did not exist, this function would still operate correctly during a self-assignment (because all of the operations done by the function can handle self-assignment properly).

Because self-assignment is a rare event, some prominent C++ gurus recommend omitting the self-assignment guard even in classes that would benefit from it. We do not recommend this, as we believe it’s a better practice to code defensively and then selectively optimize later.

The copy and swap idiom

A better way to handle self-assignment issues is via what’s called the copy and swap idiom. There’s a great writeup of how this idiom works on Stack Overflow .

The implicit copy assignment operator

Unlike other operators, the compiler will provide an implicit public copy assignment operator for your class if you do not provide a user-defined one. This assignment operator does memberwise assignment (which is essentially the same as the memberwise initialization that default copy constructors do).

Just like other constructors and operators, you can prevent assignments from being made by making your copy assignment operator private or using the delete keyword:

Note that if your class has const members, the compiler will instead define the implicit operator= as deleted. This is because const members can’t be assigned, so the compiler will assume your class should not be assignable.

If you want a class with const members to be assignable (for all members that aren’t const), you will need to explicitly overload operator= and manually assign each non-const member.

Tech Differences

Know the Technical Differences

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.

Related Differences:

• Difference Between & and &&
• Difference Between Recursion and Iteration
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Copy Constructor in C++: Syntax, Types and Examples

Are you curious to know about copy constructors in C++ programming language? They are a great way to optimize and streamline the duplication of objects. But do you know how they work, what their types are, or why they are so important? In this blog post, we’ll cover all aspects of these powerful features. So, let’s begin understanding what copy constructors do and how to successfully implement them into your codebase.

Table of Contents

Introduction to Constructors

Constructors in C++ are methods invoked automatically at the time of object creation to initialize the data members of the new objects. It has the same name as the class and is called a constructor because it constructs or provides the values for the object. A restriction that applies to a constructor is that it must not have a return type or void.

The following is the syntax for defining a constructor:

You should declare a constructor in the public section of the class, as it is invoked automatically when objects are created. Further, there are three types of constructors in C++: default, parameterized, and copy constructors. 

In a default constructor, no argument is passed, and it is known as a constructor with no parameters. Parameterized constructors allow one or more arguments to pass. Copy constructors create an object based on the previously created object of the same class. 

Constructors and similar C++ concepts are part of the core proficiencies required in data science, web development, and related domains. If you wish to pursue a career in these fields, check out trending job oriented courses with internship or job placement offers. 

Copy Constructor Syntax in C++

The syntax of copy structure in C++ is “ClassName(const ClassName &objectToCopy)”, where “const” indicates no modification to the original object when copying will be made. For example, you have two strings, ‘stringA’ and ‘stringB’. If you wanted ‘stringB’ to take on all properties associated with ‘string A’, without modifying ‘stringA’, then using a copy constructor would do just that.

In this case, “obj2” is created as the new object, which will take on the same values as what was previously seen in “obj1”. To learn more about copy constructor and its syntax, consider opting for an in-depth C++ course .

Example of Copy Constructor in C++

The copy constructor of the Rectangle class is used to create a duplicate object of an existing one by copying its contents. The code for this operation is as follows: 

The constructor of this object takes a parameter that is a reference to another Rectangle class instance. This means the values stored in obj’s variables are then assigned to the new object, invoking the copy constructor and effectively copying all data from one object into another. In main(), two rectangle objects, rect1 and rect2 have been created and an example has been given where the contents of rect1 were copied over onto rect2 using this method.

In this instance, the rect2 object invokes its copy constructor by passing a reference to the rect1 object as an argument – namely &obj = &rect1. This is done for constructors to fulfill their purpose of initializing objects and executing default code when they are created.

Also Read: Array in C

Characteristics of Copy Constructor

The following are the key characteristics of a Copy Constructor:

• It is used to initialize a new object’s members by duplicating the members of an existing object. It accepts a reference to an object of the same class as a parameter. 
• Copy initialization involves using the copy constructor, which carries out member-wise initialization; copying each individual member respectively between objects of identical classes. 
• If not specified explicitly, this process will be handled automatically by compiler-generated code for creating such constructors within programs. These programs can be written in C++ language or similar languages that support Object Oriented Programming (OOP).
• The copy constructor is useful for creating copies of existing objects without having to redefine the object’s entire data structure and attributes again. 
• It also allows a programmer to provide custom modifications while copying an object, such as altering members according to certain criteria or making other changes. These changes can be more difficult in regular ‘assignment’ type operations between two identical classes of objects

Types of Copy Constructors in C++

A copy constructor program in C++ program is categorized into the following two types. 

1. Default Copy Constructor

A default copy constructor is an implicitly defined one that copies the bases and members of an object like how they would be initialized by a constructor. The order in which these elements are copied during this process follows the same logic of initialization used when creating new objects with constructors.

2. User-Defined Copy Constructor

A user-defined copy constructor is necessary when an object holds pointers or references that cannot be shared, such as a file. In these cases, it’s recommended to also create a destructor and assignment operator in addition to the copy constructor. 

A user-defined copy constructor may be necessary when an object contains pointers or any kind of runtime resource allocation, such as file handles or network connections. With a custom copy constructor, it is possible to achieve deep copies instead of the shallow ones created by default constructors. The user can ensure that the pointers in copied objects are directed toward new memory locations with this method.

When is the Copy Constructor in C++ Used?

A copy constructor is called when an object of the same class is: 

• Returned by value 
• Passed as a parameter to a function 
• Created based on another object of the same class  
• When a temporary object has been generated by the compiler

Though a copy constructor may be called in some instances, there is no guarantee that it will always be used. The C++ standard allows for the compiler to eliminate redundant copies under specific conditions such as return value optimization (commonly referred to as RVO).

Difference Between Copy Constructor and Assignment Operator

Differences between initialization and assignment in c++.

In the following code segment:

The variable “b” is initialized to “a” since it is created as an exact copy of another variable. This implies that when we create “b”, its value will go from containing unwanted data directly to holding the same value immediately without any intermediate step.

On the other hand, in this revised code example:

The statement “MYClass a, b;” initializes two variables – ‘a’ and ‘b’. The second line of code “b = a” assigns the value contained in variable ‘a’ to another (variable) object ‘b’. This demonstrates the difference between assignment and initialization. Assigning new values or instructions to an existing variable is known as an assignment. On the other hand, when objects receive values at their time of creation, it is referred to as initialization.

Copy constructors in C++ are an essential tool for effective software programming. Not only do they allow for objects to be efficiently duplicated within code, but they also provide better resource and memory management when dealing with pointers or other runtime resources. Programmers must understand the differences between initialization and assignment and master using these copy constructors to create great applications.

Are you a programmer looking for jobs in this domain? Check out this guide on C++ interview questions with proper coding examples to help you crack your next interview with ease.

In C++, the default constructor has an empty body and does not assign default values to data members. The copy constructor is not empty and copies all data members of the passed object to the newly created object. 

When the copy constructor is declared private, you cannot copy the class’s objects. It is useful when the class has pointer variables or dynamically allocated resources.

Yes, we can make the copy constructor private. In this case, the constructor can only be called from within the class itself. These constructors are made private when the class is not intended to be used as a standalone object but as a base class for inheritance. 

Arguments to a copy constructor must be passed as a reference to avoid unnecessary copying of objects. If an argument is passed by value, the copy constructor is called indefinitely to make a copy of the argument. This results in an infinite loop.

The argument in a copy constructor should be const because const reference enables you to read the value but not modify it within the function. This ensures that the objects are not accidentally modified. Const argument is essential while working with temporary objects.

Copy constructors are required in C++ to initialize the data members of a newly created object in a class by copying the data members of an existing object of the same class. 

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Copy Constructor in C++ vs. Assignment Operator in C++: What's the Difference?

Key Differences

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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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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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• When is copy constructor called in C++?

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How to Implement a Copy Constructor for Deep Copying?

In C++, the copy constructor enables us to initialize an object using another object of the same class. In this article, we will learn, how to implement a copy constructor for deep copying.

Implementing a Copy Constructor for Deep Copying

In C++, a copy constructor is used to create a copy of an object from an existing object of the same class. By default, the compiler-generated copy constructor creates a shallow copy which means if the object contains pointers to dynamically allocated memory, both the original and the copied objects will point to the same memory location so the changes made through one object’s pointer will affect the other object, which might lead to unintended behavior or errors.

To ensure each object has its own independent copy of dynamically allocated memory, we can explicitly define a deep copy constructo r that allocates separate memory for the copied object’s pointers, thus ensuring changes in one object do not affect the other.

C++ Program to Implement a Copy Constructor for Deep Copying

The below example implements a copy constructor to create a deep copy of an object that has a character array as a data member.

Time Complexity: O(N), here N denotes the size of the dynamic object. Auxiliary Space: O(N)

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