iterating objects

[marlowe]

What is it called when you iterate objects? ex:

class snake
{
public:
void setAge(int a) {_age=a;}
int getLength();
private:
int _age;
}

int snake::getLength()
{
int age;
std::cin>>age;
setAge(age);
return age*3;
}

int main()
{
snake mary,joe,betty;
int numSnakes=3,length;
for(int i=0;i<numSnakes;i++)
{
length=SNAKE.getLength()
std::cout<<"The length of snake "<<SNAKE<<" is "<<length<<std::endl;
}
return 0;
}

where the program would iterate SNAKE as mary, joe and betty.

[1yR4jE8b]

ummmmmm....I think you answered your own question there buddy....

iterate

[kempofighter]

That code doesn't make any sense. What is SNAKE? It isn't even a valid object or container. Does it compile?

[moorecm]

I think the question is more along the lines of what is an array or container...

[Galik]

If you want to iterate through your three defined snakes mary, joe and betty then you need to put them in some kind of container.

You could put them in a std::vector for instance:

#include <vector>

int main()
{
    snake mary, joe, betty;

    std::vector<snake> pit;
    
    pit.push_back(mary);
    pit.push_back(joe);
    pit.push_back(betty);

    std::vector<snake>::iterator i;
    for(i = pit.begin(); i != pit.end(); ++i)
    {
        std::cout << "The length of snake " << *i << " is " << i->getLength() << std::endl;
    }

    return 0;
}

[helios]

Oh, I get it.

What is it called when you iterate objects?

It's called nothing, because you can't do that. Well, not directly, anyway.

T a,b,c;
T *array[]={&a,&b,&c,0};
for (int i=0;array[i];i++)
    array[i]->f();

[marlowe]

Do i need to do something special here with the vector pointer *i? I am getting an error in relation to the pointer.

[kempofighter]

Okay, I see the problem. There is no operator<< for snake objects and there is no accessor for the _age attribute. So make an accessor and use it instead of *i. You cannot send a snake object to operator<< without defining that operator for the type. Don't have time to do that right now but let me show you something else.

#include <vector>

int main()
{
    snake mary, joe, betty;

    std::vector<snake> pit;
    pit.reserve(3); // reserve for 3 otherwise the push_back might create more memory than needed.
    pit.push_back(mary);
    pit.push_back(joe);
    pit.push_back(betty);
    
    // first initialize i and end at the beginning
    // second, if you want to name the snake then create attribute, accessor for it and send that
    // to stream.  Or define operator<< for snake and send *i to operator<<.
    for(std::vector<snake>::iterator i = pit.begin(), end = pit.end();; i != end; ++i)
    {
        std::cout << "The length of snake " << " is " << i->getLength() << std::endl;
    }

    return 0;
}

Perhaps someone else can show you the operator<< or you can google for that.

[Galik]

You can't output the literal names "mary", "joe" and "betty" unless you include them in the class:

#include <string>
#include <vector>

class snake
{
public:
    snake(const std::string& name): _name(name) {}
    void setAge(int a) {_age=a;}
    int getLength();
    std::string getName() { return _name; }
private:
    int _age;
    std::string _name;
}

Then you can print their names:

#include <vector>

int main()
{
    snake mary("Mary"); // give them names
    snake joe("Joe");
    snake betty("Betty");

    std::vector<snake> pit;
    pit.reserve(3); // reserve for 3 otherwise the push_back might create more memory than needed.
    pit.push_back(mary);
    pit.push_back(joe);
    pit.push_back(betty);
    
    for(std::vector<snake>::iterator i = pit.begin(), end = pit.end(); i != end; ++i)
    {
        std::cout << "The length of snake " << i->getName() << " is " << i->getLength() << std::endl;
    }

    return 0;
}