How to write a class in c++ with proper iterators so it can be used by standard library containers and algorithms

Question

Suppose I wrote a class in c++ like this:

class data
{
private:
    int a,b,c,d;
public:
    data(){
        a=b=c=d=0;
    }
    data(int aa,int bb, int cc, int dd)
    {
        a=aa,b=bb,c=cc,d=dd;
    }
    int get_b(){return b;}
    int get_a(){return a;}
};

Now I know want to learn how to write operators and iterators for this class so that it can be used with standard library containers

Like: set<string> x; this is possible. I want to use this data class as set<data> x; and want to use iterators like set<data>::iterator it;

I have tried to google out the procedure, but nowhere could find an example implementation which would actually explain the procedure.

Possible duplicate of [Writing your own STL Container](http://stackoverflow.com/questions/7758580/writing-your-own-stl-container) — Amit Kumar, Jan 21 '17 at 07:45
Refer to Section 23.2.1 of the C++11 standard for requirements of the standard containers. Similarly, look in Section 24.2 for requirements of iterators. — Peter, Jan 21 '17 at 09:13
The OOP tag is wrong, because generic programming is not OOP. — Christian Hackl, Jan 21 '17 at 11:21

score 1 · Answer 1 · answered Jan 22 '17 at 04:32

If you want to use it in a std::set, std::map, std::unordered_map, std::unordered_set you need to implement a "weak less than operator"

bool operator<(const data& other_data) {
   return ....;
}

For other containers like std::vector, std::deque, std::list data is ok as it is.

instance · Accepted Answer · 2017-01-22T15:39:15.877

Like: set x; this is possible. I want to use this data class as set x; and want to use iterators like set::iterator it;

I believe you want to use you class as data to fit into standard containers (vector/set etc).

For Sequence Containers (Vector)

int main()
{
    data d1(1, 2);
    data d2(3, 4);

    vector<data> vec{d1, d2};  //initialize your container with your "data" type objects.
    for(auto iter = vec.begin(), iter != vec.end();iter++)
        cout<<*iter;     //for this you need to implement "operator<<" in your data class.    
    return 0;
}

For Associative Containers (Set)

int main()
{
    data d1(1, 2);
    data d2(3, 4);
    //you need to impelment "< or >" relational operator in you data class.
    set<data> st{d1, d2};  //initialize your container with your "data" type objects.
    for(auto iter = vec.begin(), iter != vec.end();iter++)
        cout<<*iter;     //for this you need to implement "operator<<" in your data class.    
    return 0;
}

Add this in your class definition.

friend ostream& operator<<(ostream& os, const base& obj)
{
    return (os<<obj.memVariable);
}

@AkaSaito no, i meant output stream operator..added it in my answer above. — instance, Jan 22 '17 at 15:37

How to write a class in c++ with proper iterators so it can be used by standard library containers and algorithms

2 Answers2