Operator Assignment

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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.

(For a vec, a new element can only be added to the right-hand end.) We can assign to the elements of a string, as follows: The left-most single character from the right-hand operand is stored at the designated location; all other characters in the right-hand operand string are ignored.

If the designated location is beyond the end of the destination string, that string is extended to the new length with spaces (U 0020) added as padding beyond the old end and before the newly added character.

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. It's a good way to test a programmer's grasp of C syntax and C style, but more importantly, it tests the programmer's knowledge of C memory management and exception handling. We'll go through it all piece by piece and see why this is.For the impatient among you, let's cut right to the chase: One correct answer to this question would look something like this: Yes, it's a lot of code. The first reaction I usually get from people is something along the lines of "But I never have to write assignment operators." You should.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., ).If your class has no pointer members, then the shallow copy works just fine. Fraction& Fraction::operator = (const Fraction & source) By returning a reference to the calling object, you are able to chain the assignment Fraction f, g, h;f = g = h; // h assigned to g, which is assigned to f The order of evaluation of assignment operators is right to left. For a dict, if the location designated by the left-hand operand is a non-existent array element, a new element is inserted with the designated key and with a value being that of the right-hand operand.This doesn't necessarily mean that the objects are identical: some purely internal data members (such as caches) might not be copied, or data members pointing to other objects might end up pointing to different objects that are themselves semantically equivalent, rather than pointing to the same objects.The difference between the copy constructor and assignment operator is that the copy constructor is a constructor — a function whose job it is to turn raw storage into an object of a specific class.


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