Operator Assignment

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.In other words, both objects will behave the same way and return the same results when their methods are called.

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There are those that simply cannot be overloaded, and then there are those that must be overloaded as member functions of the class; they cannot be nonmember functions. The assignment operator can be defined to assign any type to an object of your user-defined type.

But we most often think of this operator as assigning an object of some type to an object of the same type. Copy assignment is very important to define correctly.

In this time, we've interviewed at least a dozen candidates and phone-screened at least a couple dozen more.

Practically every candidate we've talked to had at least two years of C experience, rated himself a 7 or 8 on a scale of 10 in C skill, and had one or two lucrative offers on the table.

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.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., ).(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.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.If the right-hand operand is an empty string, the null character [[

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.

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., ).

(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.

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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.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., ).(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.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.If the right-hand operand is an empty string, the null character \0 (U 0000) is stored. Normally, this wouldn't be such a big deal, but we've been looking for someone for a year and a half.Over this time, I've developed a stock interview question that's proven to be a pretty good gauge of C knowledge.No one has yet been able to just rip out the correct answer, but we've had several, including the guy we hired, who understood the important issues and were able to get the question right with prompting.

]] (U 0000) is stored. Normally, this wouldn't be such a big deal, but we've been looking for someone for a year and a half.Over this time, I've developed a stock interview question that's proven to be a pretty good gauge of C knowledge.No one has yet been able to just rip out the correct answer, but we've had several, including the guy we hired, who understood the important issues and were able to get the question right with prompting.