Data structure and algorithm in C++

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?

You have a function with `void` return type `return L.Last==0;`? Where is this code coming from? — amit, Sep 28 '15 at 13:59
A single `=` assigns a value, while `==` tests for equality. You might want to read [a book about C++](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) to learn more about this. — Bo Persson, Sep 28 '15 at 14:02
this code is coming from my document's lecturer. and i don't understand this — toan huynh, Sep 28 '15 at 14:05
Just pick a good C++ book it should help you to understand this kind of basic concepts. — rkachach, Sep 28 '15 at 14:06
If that's your lecturer's code, you most definitely want to follow the suggestion from @redobot — bku_drytt, Sep 28 '15 at 14:09
At least one of `L->Last` and `L.Last` is wrong, but it's impossible to tell which without seeing the definition of `List`. — molbdnilo, Sep 28 '15 at 14:27
(`->` and/or `.` might be overloaded for `List`. _amit_ is spot-on pointing out the incongruity of `void` and `return`.) The sole purpose of this snippet may be to stress the indispensability of in-line comments: _code will get separated from external documentation_. — greybeard, Sep 28 '15 at 17:41

score 0 · Answer 1 · edited May 23 '17 at 11:51

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

Thanks for your sharing :) – toan huynh Sep 29 '15 at 07:42 — toan huynh, Sep 29 '15 at 07:42

score 0 · Answer 2 · answered Sep 28 '15 at 14:30

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.

Data structure and algorithm in C++

2 Answers2