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In C , there are some special functions used with classes, some of which we have seen, like the constructor and destructor.
This is sufficient for many cases, but not for ALL cases.
Example: This fraction object has a numerator of 3 and a denominator of 4.
There are plenty of classes that don’t contain pointers that need a user-defined copy and/or move assignment operator, and there are some classes with pointers for which the implicit definitions are just the ticket.
With respect to definitions being incorrect, one factor is to ensure that resources are not unexpectedly leaked.
If this object is passed into a function by value, a copy will be made, and the new object's numerator will be 3, denominator 4. Consider, however, the Directory class of the phone book example.
Overloaded Assignment Operator Scott Monk Raw Essay
The member data variables were currentsize and maxsize (both of type int), and a pointer, entry List (of type Entry * ), which pointed to dynamically allocated data outside the actual object.
This will especially pose problems if, when the copy goes out of scope, it cleans up the dynamic data along with it.
When there is a pointer (inside an object) that points to dynamic data, the shallow copy is not sufficient, because it does not copy the dynamic data, only the pointer. Here is what we might write for a copy constructor definition in the Directory class (from the phonebook database example): Like the copy constructor, the assignment operator has to make a copy of an object. If a deep copy is desired for assignments on a user-defined type (e.g.
The explanations of the various constructs employed are given in the sections following.
I suspect what you meant to ask is: “When is it wise to explicitly define a copy and/or move assignment operator? The concise answer is: Whenever at least one of the following is true: Beware of claims that the answer depends on whether the class contains pointer members: That’s quite misleading.