C++ object instance as a class member

Question

Sorry if the title is wrong, I don't know how else to name it.

I have a class Name:

class Name {
    char * name;
public:
    Name(const char * n){
        name = new char[strlen(n)+1];
        strcpy(name,n);
    }
    Name& operator=(const Name& n){
        name = new char[strlen(n.name)+1];
        strcpy(name, n.name);
        return *this;
    }
    Name(const Name& n){
        *this = n;
    }
};

And another class Person which should have Name object as it's member. How can I do this? I was thinking something like this:

class Person{
    double height;
    Name name;
public:
    Person(double h, const Name& n){
        height = h;
        name = n;
    }
};

But only this seems to work:

class Person{
    double height;
    Name * name;
public:
    Person(double h, const Name & n){
        height = h;
        name = new Name(n);
    }
};

Is it the right way to do it, and why can't I do it like I thought in the first place? Thanks

PS. There is a memory leak in the copy constructor. Look up copy and swap idiom to help to it correctly. — Loki Astari
– Loki Astari, Commented Sep 16, 2013 at 4:58

Igor Tandetnik · Accepted Answer · 2013-09-16 04:25:09Z

2

Make the constructor like this:

Person(double h, const Name& n)
  : height(h), name(n)
{}

Then read about constructor initializer lists in your favorite C++ textbook.

The reason your original code doesn't work is that Name doesn't have a default constructor (a constructor that can be called with no parameters).

answered Sep 16, 2013 at 4:25

Igor Tandetnik

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1 Comment

yota Over a year ago

How to deal with name(n) when n must be preprocessed or is the result of some computations ? Why is this syntax so awkward ? why is C++ so syntactically bizarre :D

David Rodríguez - dribeas · Accepted Answer · 2013-09-16 04:27:29Z

1

Your Name type does not have a default constructor, so you must initialize it in the initializer list in Person. Other than that, your operator= leaks memory and is unsafe for self-assignment and you never release the memory in a destructor, so there is another leak there.

Is there a good reason not to use std::string instead of your Name type?

answered Sep 16, 2013 at 4:27

David Rodríguez - dribeas

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2 Comments

tuks Over a year ago

Thanks, I didn't mind memory leaks because I typed this code here quickly without testing it, it's just an example, not the real program I'm working on :)

David Rodríguez - dribeas Over a year ago

@tuks: You should care about memory leaks. It is much easier to think for 5 min upfront who's responsible for the lifetime of the object than try to figure out after the fact and patch every place where you leak.

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