C++中的数据结构和算法

Question

I have these two functions:

void MakeNull_List(List L){
      L->Last=0;
}

void Empty_List(List L){
      return L.Last==0;
}

So, can anyone explain this code for me? What is the difference between L->Last and L.Last ?

Answer 1

I hope that this code does NOT come from your lecturer, otherwise you should look for another one...

Sadly this code doesn't make sense because it is wrong! But I think you meant the following:

void MakeNull_List(List *L){    //* added
    L->Last=0;
}

bool Empty_List(List L){        //changed to bool
    return (L.Last==0);         //Please also use brackets here
}

The first function sets the last element to 0 (NULL) whathever sense it should make?!? The second function checks whether the last element is 0 (NULL) or not.

And your actual question: -> is used to Access properties of a pointer to an object and . accesses the properties directly of the object. For more info read here

Answer 2

Then you access object by variable or reference you should address to it fields by . . Then you have a pointer to object you should previously dereference it. So, you can write (*ptr).someField or ptr->someField .

I think, you miss * in void MakeNull_List(List *L) definition.