Operator Assignment

Operator Assignment-73
If the right-hand operand is an empty string, the null character If the right-hand operand is an empty string, the null character

But as it is with the compiler generated copy constructor, it will be a shallow copy: every member of the class is copied from the source to the target without consideration to pointer problems. As a public service, I'd like to share my stock question and its answer with you and explore the various programming issues it presents.The question is as follows: This seems like a simple enough exercise, but it gets at some interesting issues.These three functions are special in C : If you don't provide them yourself, C provides them for you. Among other things, this means you have to define these operations even if you don't want a client to be able to copy or default-construct a particular class.If you don't want a class to be copied, for example, you have to define an empty copy constructor and assignment operator yourself and make them private or protected.Always give any new class a default constructor, a copy constructor, and an assignment operator.Another misconception I see often is a fuzzy idea of the difference between the copy constructor and the assignment operator.If your class has pointer members, this is practically never what you want, and even when you don't have pointer members, this isn't always the right behavior. Even when the default versions of the special functions do what you want them to, it's still generally a good policy to always spell that out explicitly by writing them yourself.It avoids ambiguity, and it forces you to think more about what's going on inside your class.Furthermore, the compiler isn't guaranteed to create versions of these classes that do exactly what you want them to do.For copying and assignment, for example, the automatically-generated code will do a shallow memberwise copy.

(U 0000) is stored. (U 0000) is stored.

[[ If the right-hand operand is an empty string, the null character \0 (U 0000) is stored. || If the right-hand operand is an empty string, the null character \0 (U 0000) is stored. ]]

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An assignment operator, on the other hand, copies state between two existing objects.

In other words, an assignment operator has to take into account the current state of the object when copying the other object's state into it.

If you've ever created a new class, you've needed to write an assignment operator. In C , there are three things every object is expected to be able to do: An object should be able to initialize itself to a default state, it should be able to initialize itself from another instance of the same class, and it should be able to assume the semantic state of another instance of the same class.

In C , these operations are expressed with the default constructor (e.g., ).

However, it may not be necessary to define it since once again, the compiler will generate a definition for the (copy) assignment operator.

[[

But as it is with the compiler generated copy constructor, it will be a shallow copy: every member of the class is copied from the source to the target without consideration to pointer problems.

As a public service, I'd like to share my stock question and its answer with you and explore the various programming issues it presents.

The question is as follows: This seems like a simple enough exercise, but it gets at some interesting issues.

These three functions are special in C : If you don't provide them yourself, C provides them for you. Among other things, this means you have to define these operations even if you don't want a client to be able to copy or default-construct a particular class.

If you don't want a class to be copied, for example, you have to define an empty copy constructor and assignment operator yourself and make them private or protected.

||

But as it is with the compiler generated copy constructor, it will be a shallow copy: every member of the class is copied from the source to the target without consideration to pointer problems. As a public service, I'd like to share my stock question and its answer with you and explore the various programming issues it presents.The question is as follows: This seems like a simple enough exercise, but it gets at some interesting issues.These three functions are special in C : If you don't provide them yourself, C provides them for you. Among other things, this means you have to define these operations even if you don't want a client to be able to copy or default-construct a particular class.If you don't want a class to be copied, for example, you have to define an empty copy constructor and assignment operator yourself and make them private or protected.Always give any new class a default constructor, a copy constructor, and an assignment operator.Another misconception I see often is a fuzzy idea of the difference between the copy constructor and the assignment operator.If your class has pointer members, this is practically never what you want, and even when you don't have pointer members, this isn't always the right behavior. Even when the default versions of the special functions do what you want them to, it's still generally a good policy to always spell that out explicitly by writing them yourself.It avoids ambiguity, and it forces you to think more about what's going on inside your class.Furthermore, the compiler isn't guaranteed to create versions of these classes that do exactly what you want them to do.For copying and assignment, for example, the automatically-generated code will do a shallow memberwise copy.

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