C++ Constructor setting value

Question

I am trying to write a constructor in C++ (I am new).

My Attempt:

class Tree
{
    private:
        int leaf;

    public:
        Tree(int leaf); //constructor
};

Tree::Tree(int leaf) //constructor
{
strcpy(this->leaf, leaf);
}

Is this the proper way how to do it? Since I found many different version with srcpy, without , etc.

possible duplicate of [Initializing fields in constructor - initializer list vs constructor body](http://stackoverflow.com/questions/9903248/initializing-fields-in-constructor-initializer-list-vs-constructor-body) — ManuelH, Jan 05 '14 at 21:35
Would you kindly do us a favour and help us understand how people learn C++ -- please explain *why* did you feel that `strcpy` was appropriate here? I'm genuinely curious about the thought process. — Kerrek SB, Jan 05 '14 at 21:37
I'm sorry to see that you did not read [my answer on your previous question](http://stackoverflow.com/a/20939216/560648), or Google `strcpy` to find out what it does. — Lightness Races in Orbit, Jan 05 '14 at 22:03
@LightnessRacesinOrbit "What does this code do? It burns the eyes of children." Hahaha — Proxy, Jan 05 '14 at 22:56

score 7 · Answer 1 · answered Jan 05 '14 at 21:34

No, it is not. strcpy is for copying null-terminated strings. Use the constructor initialization list:

Tree::Tree(int leaf) : leaf(leaf) {}

Also note that your constructor allows for implicit conversions from int to Tree. So you can do this kind of thing:

Tree t = 4 + 5;

If you do not want this behaviour, mark the constructor explicit:

explicit Tree(int leaf);

score 1 · Answer 2 · edited Jan 05 '14 at 21:45

1

You can simply initialize the int like this:

Tree::Tree(int leaf) //constructor
  : leaf(leaf)
{
}

strcpy is not needed, it is meant for C-strings. It does not compile since it expects a char* pointer.

edited Jan 05 '14 at 21:45

leemes

44,967
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answered Jan 05 '14 at 21:34

cageman

333
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so if you use a string (char* ) you have to use strcpy then? – user3126119 Jan 05 '14 at 21:37
@user3126119, I suggest using a `std::string` and doing the exact same thing as this. @cage, It initializes it, not assigns. – chris Jan 05 '14 at 21:43
Do yourself a favor and don't use C-strings (char*). Use C++ strings (`std::string`) which can be initialized like your `int`. – leemes Jan 05 '14 at 21:44
@cageman it's initialization, not assignment. Also, `strcpy` [won't compile](http://ideone.com/teActm) here, fixed that in your answer. – leemes Jan 05 '14 at 21:47
can you edit my code with std::string since I cannot figure how to do it I have been trying and still no success. I would appreciate a lot – user3126119 Jan 05 '14 at 22:44

score 0 · Answer 3 · answered Jan 05 '14 at 23:02

You can use std::copy if you really want to use some sort of memory-copying function, but m_leaf = leaf works just as well and is easier to read. Notice my use of m_leaf instead of leaf - it's common to add the prefix m_ before all member variables (More on Hungarian Notation here).

C++ Constructor setting value

3 Answers3