The string you think is the same as expected is no the same as expected, it just seems to be the same as expected. Due to an off-by-one bug in your solution, it has a stray \0' in the middle. Change the bottom of your function to:

  std::cout<<strr << std::endl;
  for(char c: strr) {
    std::cout << (int)c << ' ';
  }
  std::cout << std::endl;
  
  return strr;
}// spinWords

... and you will see that first space is not a space but \0.