C++ assignment operator, can we replace it with copy?

Question

When I was reading:

What's the difference between assignment operator and copy constructor?

here: What's the difference between assignment operator and copy constructor?

The following example was shown:

A aa;
A a = aa;  //copy constructor

vs:

A aa;
A a;
a = aa;  // assignment operator

and my question is, why we need the assignment operator at all? I mean that it will be more efficient to use the copy constructor in this case while it does the same job.

could someone give a real-world example of the use of assignment operator where that can't be replaced by the copy constructor?

Answer 1

You need assignments when you want to change a value after it has already been constructed. For example:

• change a value that is already stored in a std::map
• change the nth value inside a std::vector
• change the value of a variable outside a loop
• change the value of an output parameter provided as a pointer or reference
• ...

The list could really go on almost endlessly. But in your example it is true that one could simply avoid the use of an assignment.