Question

The below is an exam question:

    /* 1 */ string s1 = "FRED";
    /* 2 */ string s2 = s1;
    /* 3 */ string s3 = "DERF";
    /* 4 */ s3 = s1;

For the second and the fourth lines above, name what type of statement that line is. Will
they call the same member function of class string? [5 marks]

So my answer:

• Line 2 is initializing a new string object s2 using the copy constructor to copy over all the member variables from s1 into the s2.
• Line 4 is also copying over all the member variables from s1 into s2, but it is overloading the assignment operator (operator=) to do so.

Therefore they both are calling 2 different member functions.

Is the above an acceptable answer? Is there anything I can add of do I have the wrong idea?

Answer 1

About your answer regarding Line #4

You cannot be certain that it actually makes use of the copy constructor, and it absolutely shouldn’t.

Why create a temporary object inside std::string::operator= when you could copy the data from s1 into s3 directly?

What you wrote about operator= is correct, but leave out what you wrote about the copy-constructor there. There is no initialization of a new object, therefor no constructor should be called.

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You should also leave out the statement regarding making copies of all the member variables, that doesn’t have to be true.

And when it comes to objects such as std::string there are pointers as members that aren’t copied, but the memory where they point are being copied into a new memory space (to be used by the destination object).

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Post OP edit of his/hers post..

OP just changed his post deleting what I made a remark on in the first part of this post.