Why is the copy constructor not called in this C++ code?

Asked Aug 09 '15 at 17:15

Active Aug 09 '15 at 17:15

Viewed 36 times

I have a simple class Employee that has three strings (first, middle and last names) and defines copy and move constructors and assignment operators and prints a text when each one is called. I also have this code in my main class

int main() {
    Employee e = getEmp();

    return 0;
}

Employee getEmp() {
    Employee emp("John","","Smith");
    return emp;
}

And here's the output:

This is Employee constructor
This is Employee destructor

So the copy or move constructors are never called and only one Employee is created, whereas I was expecting a call to the move constructor when getEmp() returns. What is happening?

asked Aug 09 '15 at 17:15

user798275

#RVO# A topic that has been discussed million times here... – SwiftMango Aug 09 '15 at 17:17
Return value optimization is happening: search for RVO – Vittorio Romeo Aug 09 '15 at 17:17
Shouldn't RVO call the move constructor? – Kam Aug 09 '15 at 17:22
4

@Kam: Nope. RVO (or more generally, copy elision) eliminates copy and move constructor calls entirely, by constructing the source object in the memory location of the destination object. – Benjamin Lindley Aug 09 '15 at 17:25
Thanks guys! Sorry for the duplicate question – user798275 Aug 10 '15 at 08:59

Why is the copy constructor not called in this C++ code?

0 Answers0