For range loop question

[danny191]

Halo

i am wondering about the For range loop with a class.
it a little bit confused me..

  bool Movies::increment_watched(std::string name){
    for(Movie &m: movies){
        if(m.get_name() == name){
            m.increment_watched();
            return true;
          } else {
        std::cout << " The movie is not exist in the list" << std::endl;
        return false;
          }
    }         
}

this code is part of a bigger code that let the user add movies to a vector (movies) and to increment the number of time the movie been watched.

1.in that part: "for(Movie &m: movies)" what is the "m" ? a variable or a
object of class Movie?
if "m" is an object so an constructor is been calling yes? also copy
constructor?
2. if instead of the class name "Movie" i will put "auto" it will
be the same?
3. why we needed the reference before the "m" in this case?


thank you

[jlb]

You may want to look up Ranged based loops for the answer to these questions.

Here is but one example:

https://www.geeksforgeeks.org/range-based-loop-c/

[ne555]

void foo(Movie &m);

int answer = 42;
int &bar = answer;

T &sdf1 = *v.begin();

¿what does the & mean in those examples?


> if instead of the class name "Movie" i will put "auto" it will be the same?
try it.
if you're asking about good programming practices, then `auto' is less error-prone.


PS: having classes `Movie' and `Movies' will get you blind

[Zaap]

1) m is a Movie here. No constructor is called, it's exactly the same than the ones in your vector.

2) Yes. Like said above, auto is less error-pprone, but I personnally prefer to always know my types.

3) You need a reference because it seems that the increment_watched() function modify the object. If you don't pass a reference, it will modify a copy (so nothing).
Note that sometimes you can pass const & on big objects (actually everything which is bigger than a long long type) to save memory space without modifying the object.