Errors when initializing class with an array as a member variable in C++

Question

I'm just starting to learn C++ and can't figure out what I'm doing wrong.

I'm trying to build a class "Holder" that holds an array of up to 100 of another class "Obj". I have the following two classes:

class Obj {
public:
    Obj(int k, char v): key(k), val(v) {};
private:
    int key;
    char val;

   friend class Holder;
};


class Holder {
private:
    enum {MAX_SIZE = 100};
    Obj p[MAX_SIZE];
    int pSize = 0;
public:
    Holder();
    ~Holder();
//...
};

When initializing the class Holder from main(), as follows...

int main() {
    Holder test;

    return 0;
}

I'm receiving these errors after running the program:

undefined reference to "Holder::Holder()" and undefined reference to "Holder::~Holder()"

I can't tell if I'm correctly using an array as a class member variable in "Holder"? Or if I'm missing something in the constructor?

You are showing the declarations of your constructor and destructor for Holder but where are the definitions? — super
– super, Commented Mar 27, 2018 at 4:53
Is it your wish that the compiler will generate the c'tor and d'tor for Holder? — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented Mar 27, 2018 at 4:55

ObliteratedJillo · Accepted Answer · 2018-03-27 05:11:50Z

0

Try this code snippet. Since constructor of Holder will require auto initialization of an Obj array, a default constructor is used :

class Obj {
public:
    Obj() :key(0),val(0){};   //Additional - default constructor
    Obj(int k, char v): key(k), val(v) {};
private:
    int key;
    char val;

   friend class Holder;
};


class Holder {
private:
    enum {MAX_SIZE = 100};
    Obj p[MAX_SIZE];
    int pSize = 0;
public:
    Holder(){}   // constructor definition 
    ~Holder(){}   // destructor definition 
//...
};

int main()
{
    Holder test;
}

answered Mar 27, 2018 at 5:11

ObliteratedJillo

5,1642 gold badges15 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

juanchopanza Over a year ago

Removing the user defined constructor and destructor would be a better idea. That at least lets the user zero-initialize using value initialization.

juanchopanza Over a year ago

Also the error has nothing to do with the data members.

sato_jessica Over a year ago

This got rid of the error! Thanks a lot for your reply, seccpur!

Tronic · Accepted Answer · 2018-03-27 07:27:07Z

-1

Consider using std::array (or std::vector) and perhaps also std::pair instead of Obj.

std::array<std::pair<int, char>, 100> p;  // Will automatically init with zeroes
// Example of using it:
p[50] = std::make_pair(1234, 'a');
std::cout << "key:" << p[50].first << ", val:" << p[50].second << std::endl;

answered Mar 27, 2018 at 7:27

Tronic

1,42615 silver badges16 bronze badges

1 Comment

Tronic Over a year ago

Someone downvoted -- maybe you could also comment why this is not good?

Collectives™ on Stack Overflow

Errors when initializing class with an array as a member variable in C++

2 Answers 2

3 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related