Move of local variable that have move c-tor into function with parameter by value

Question

Trying to clear my understanding when move happens, and when it's better to write functions that pass values by value, instead of reference, to gain from moves.

void foo()
{
  std::string localStr;
//
  foo1(localStr);
}
void foo1(const std::string str)
{

}

Will in this case localStr be moved into foo1?

And if to add one more level of functions call:

void foo()
{
  std::string localStr;
//
  foo1(localStr);
  //localStrisn't used anymore
}
void foo1(const std::string str)
{
   foo2(str);
   //str isn't used anymore
}
void foo2(const std::string str)
{
}

Will there be two moves?

There are no *moves* being performed in this code at all. Both examples are making *copies* instead. A *move* would look more like this: `foo1(std::move(localStr));` (`foo2(std::move(str));` would not be valid since `str` is `const` and so can't be moved from). — Remy Lebeau, Mar 03 '21 at 18:43
Note that you may get "move-like" behaviour if the compiler determines that it can get away with it without anyone noticing. See the [As-if Rule](https://en.cppreference.com/w/cpp/language/as_if). — user4581301, Mar 03 '21 at 18:47

score 0 · Answer 1 · answered Mar 03 '21 at 18:34

0

You pass a copy of str by value. It's not moved. If you use a pointer or reference only an address is copied.

answered Mar 03 '21 at 18:34

Allan Wind

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Move of local variable that have move c-tor into function with parameter by value

1 Answers1