Here's a program that uses only std::unique_ptr:

  #include<iostream>
  #include<memory>
  
  int main() {

      std::unique_ptr<int> null_ptr;
    
      std::cout << *null_ptr << std::endl; // Undefined behavior
  }

Clang 20 compiles this code with `-std=c++23 -Wall -Werror`. If you add -fsanitize=undefined, it will print

  ==1==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address 0x000000000000 (pc 0x55589736d8ea bp 0x7ffe04a94920 sp 0x7ffe04a948d0 T1)

or similar.