C++ Is the copy constructor called here?

Question

Suppose you have a functions like this:

Foo foo() {
  Foo foo;

  // more lines of code

  return foo; // is the copy constructor called here?
}

Foo bar() {
  // more lines of code

  return Foo(); // is the copy constructor called here?
}

int main() {
  Foo a = foo();
  Foo b = bar();  
}

When any of the functions return, is the copy constructor called (suppose there would be one)?

Answer 1

It might be called, or it might not be called. The compiler has the option of using the Return Value Optimization in both cases (though the optimization is a bit easier in bar than in foo ).

Even if RVO eliminates the actual calls to the copy constructor, the copy constructor must still be defined and accessible.

Answer 2

取决于是否应用返回值优化 。

Answer 3

It may be called. It also may be optimized away. See some other question in the same direction.