CODEWITHSUNDEEP
c++classvector
networks
networks

Reputation: 115

classname as an object to vector and argument to function to push_back

I have this small program as i am trying to understand the vector and the classname being passed as an argument. Here is the program:

#include<iostream>
#include<vector>
using namespace std;

class objectclass{
public:
    void vec_try(){
        cout<<"print out something";
    }
};

class another{
public:
    void run();
    vector<objectclass *>ports;
    void add_obj(objectclass *p){
        ports.push_back(p);
    }
    };

void another::run(){
    //int j=0;
    ports[j]->vec_try();
}
int main(){
another a;
a.run();
system("pause");
return 0;
}

i have idea that passing classname in vector as an object is fine and then using push_back to insert the element in that vector but in the function add_obj(objectclass *p) how do i pass the values if i dont want to change the defination of the function. i know a way like this:

objectclass *p;
p= new objectclass[10];

but my function has already defination and also i want to call the function vec_try() with ports[i] so i am not getting how to pass the values and the how this is working with ports[i]. i basically need some clarification on this.

Upvotes: 0

Views: 701

Answers (1)

Joseph Mansfield
Joseph Mansfield

Reputation: 110658

Your add_obj function takes pointers to objectclass objects. So to add elements to your vector, you need to do:

another a;

objectclass obj1;  // Create an objectclass
a.add_obj(&obj1);  // Pass its address to add_obj

objectclass obj2;
a.add_obj(&obj2);

objectclass obj3;
a.add_obj(&obj3);

Of course, your vector is keeping pointers to these objects. When these objects go out of scope and are destroyed, these pointers will be left pointing at invalid object. But that doesn't matter here, because your objects are only destroyed at the end of main.

An alternative would be to dynamically allocate your objects:

another a;
a.add_obj(new objectclass());
a.add_obj(new objectclass());
a.add_obj(new objectclass());

Each line dynamically allocates an objectclass object, then passes a pointer to that object to add_obj. However, you will need to make sure that you eventually delete this objects in some way or another.

The first element that you push_back into the vector will have index 0, the second will have index 1, the third will have index 2, and so on.

If in run, you want to iterate over all objects in the vector, you can do it something like this:

for (int i = 0; i < ports.size(); i++) {
  ports[i]->vec_try();
}

As you can see, this loops through all the elements in the vector (from 0 to ports.size()) and calls vec_try on each one.

There is a better way to do this using iterators, but I'll leave that for a future lesson.

Upvotes: 1

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