C++ reference to rvalue stays valid

Asked Feb 18 '22 at 13:29

Active Feb 18 '22 at 13:37

Viewed 15 times

I have a class Foo that store a const reference to a Bar. If I pass a temporary Bar to the constructor, I thought that storing that would be bad, but it works correctly. Does storing the rvalue somehow extend the lifetime of the temporary?

#include <iostream>

struct Bar {
  int a;
};

struct Foo {
  Foo(const Bar& bar) : bar{bar} {}
  
  const Bar& bar;
};

int main() {
  Bar bar{5};
  Foo foo{bar};
  Foo foo2{Bar{10}};

  std::cout << foo.bar.a << std::endl; // Prints 5, OK
  std::cout << foo2.bar.a << std::endl; // Prints 10, why?
}

asked Feb 18 '22 at 13:29

Jojolatino

I think this is the proper duplicate: https://stackoverflow.com/questions/2784262/does-a-const-reference-class-member-prolong-the-life-of-a-temporary – ChrisMM Feb 18 '22 at 13:35
What you actually have is undefined behaviour. – ChrisMM Feb 18 '22 at 13:37
Yes, the code fails if you enable optimisations: https://godbolt.org/z/rKG7W5zGx – Alan Birtles Feb 18 '22 at 13:37

C++ reference to rvalue stays valid

0 Answers0