How to reach a member function of objects in a vector?

cpit · #1 29-Oct-2009, 09:43

Hi all,

I'm trying to create a vector of objects but I didn't figure out how to reach the member function of objects inside the vector.

Here is my code:

CPP / C++ / C Code:

vector<Node> nodes;
 for (int i=0; i<10; i++){  
 	 Node *ntemp = new Node;   
 	 	ntemp->setId(i); 	 	
     nodes.push_back(*ntemp);
 }

Now, I would like to reach the member functions of objects in each position of the vector nodes (nodes[0], nodes[1]...).

Thanks in advance for the replies.

Kimmo · #2 29-Oct-2009, 10:03

You can use operator[]() or at(). Both return an element at the index position you pass as an argument, only at() will throw an exception if the index is out of range.

For example

CPP / C++ / C Code:

#include <vector>
#include <iostream>

class Useless
{
public:
    
    void print() { std::cout << "Nah, it's useless. . ."; }
};

int main()
{
    std::vector<Useless> aVector(2);
    aVector.push_back(Useless());
    aVector.push_back(Useless());
    
    aVector[0].print();
    aVector.at(1).print();
    
    aVector.at(23423).print();
    
    return 0;
}

Output on my Windows XP machine:

Code:

Nah, it's useless. . .Nah, it's useless. . .
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

davekw7x · #3 29-Oct-2009, 10:17

Quote:

Originally Posted by cpit

...Now, I would like to reach the member functions...

I think the most common is by using the [] index notation. See Footnote.

If you have a member function getId() that retrieves whatever it is that gets set by setId(), then just

CPP / C++ / C Code:

int main()
{
    vector < Node > nodes;

    for (int i = 0; i < 10; i++) {
        Node ntemp;
        ntemp.setId(i);
        nodes.push_back(ntemp);
    }
    for (int i = 0; i < nodes.size(); i++) {
        cout << "nodes[" << i << "].getId() = " << nodes[i].getId() << endl;
    }

    return 0;
}

Note that your use of new inside the loop is unnecessary, and, in fact since you didn't free the memory before the next time through, it represents a memory leak. Why not just declare an object, not a pointer?

Regards,

Dave

Footnote:

The [] index notation is convenient, but it does not do bounds checking. If you try to use an index value less than zero or greater than or equal to the size of the vector, the result is undefined behavior. The loop that I showed in the example is absolutely safe since it is guaranteed to use valid index values.

In other applications, it might be safer to use vector member function at(), which will throw an exception if its argument causes it to try to access memory outside the array boundaries:

Here's the equivalent print statement using at() instead of the index notation.

CPP / C++ / C Code:

        cout << "nodes.at(" << i << ").getId() = " << nodes.at(i).getId() << endl;

cpit · #4 29-Oct-2009, 11:25

Thank you very much for the very clear responses.

Mexican Bob · #5 29-Oct-2009, 18:07

Quote:

Originally Posted by cpit

Hi all,

I'm trying to create a vector of objects but I didn't figure out how to reach the member function of objects inside the vector.

Here is my code:

CPP / C++ / C Code:

vector<Node> nodes;
 for (int i=0; i<10; i++){  
 	 Node *ntemp = new Node;   
 	 	ntemp->setId(i); 	 	
     nodes.push_back(*ntemp);
 }

Now, I would like to reach the member functions of objects in each position of the vector nodes (nodes[0], nodes[1]...).

Thanks in advance for the replies.

Here is an implementation of storing objects in a vector and invoking member functions of those objects in a couple of trivial functions; one by accessing the index of the object in the vector and the other by using an iterator.

CPP / C++ / C Code:

#include <iostream>
#include <vector>

class Box
{
public:
    Box() : m_h(0), m_w(0), m_d(0) {}
    Box(const size_t height, const size_t width, const size_t depth) :
    m_h(height),
    m_w(width),
    m_d(depth) {}
    friend std::ostream& operator<<(std::ostream& os, const Box& rhs)
    {
        os << rhs.m_h << " " << rhs.m_w << " " << rhs.m_d;
        return os;
    }
    friend std::istream& operator>>(std::istream& is, Box& rhs)
    {
        is >> rhs.m_h >> rhs.m_w >> rhs.m_d;
        return is;
    }
private:
    size_t m_h;
    size_t m_w;
    size_t m_d;

};

typedef std::vector<Box> vBoxes;

void print_vBoxes_idx(vBoxes& v)
{

    for(size_t idx = 0; idx < v.size(); idx++)
    {
        std::cout << v[idx] << std::endl;
    }
}

void print_vBoxes_it(vBoxes& v)
{
    vBoxes::iterator it;
    for(it = v.begin(); it != v.end(); it++)
    {
        std::cout << *it << std::endl;
    }
}

int main()
{
    vBoxes v;
    Box b1(1, 2, 3);
    Box b2(10, 20, 30);
    Box b3(100, 200, 300);
    Box b4;

    v.push_back(b1);
    v.push_back(b2);
    v.push_back(b3);
    v.push_back(b4);


    print_vBoxes_idx(v);
    std::cout << std::endl;
    print_vBoxes_it(v);

    return 0;
}

Output:

Code:

$ ./vobjects
1 2 3
10 20 30
100 200 300
0 0 0

1 2 3
10 20 30
100 200 300
0 0 0

MxB

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Rate This Thread
Rate This Thread:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
run script command on ns2.26	newbie06	Computer Software Forum - Linux	65	19-Aug-2009 08:50
Problem executing nam-1.13	RodolfoAlvizu	Computer Software Forum - Linux	20	28-Feb-2009 16:23
Major newbie problem	cynack	MS Visual C++ / MFC Forum	1	08-Apr-2007 12:25
Combining Vectors and References	Frankg	C++ Forum	7	14-Jan-2006 07:17
[Tutorial] GUI programming with FLTK	dsmith	FLTK Forum	10	03-Oct-2005 16:41

How to reach a member function of objects in a vector?

Re: How to reach a member function of objects in a vector?

Re: How to reach a member function of objects in a vector?

Re: How to reach a member function of objects in a vector?

Re: How to reach a member function of objects in a vector?