Jump to content
  • Advertisement
Sign in to follow this  
autir

C++ vector of objects problem

This topic is 3990 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi all. When compiling the following
#include <iostream>
#include <vector>
using namespace std;

class being
{
private:
 int hp;
public:
 being();
 being(int);
 ~being();
 int hit_points(void);
 void set_hp(int);
};

being::being()
{
cout<<"Creating a being."<<endl;
hp=0;
}

being::being(int i)
{
cout<<"Creating a being with "<<i<<"hp."<<endl;
hp=i;
}

being::~being()
{
cout<<"Destroying a being."<<endl;
}

int being::hit_points(void)
{
return hp;
}

void being::set_hp(int i)
{
hp=i;
}

main()
{
int i;
int crit=5;
vector<being> critters(crit);
cout<<"Construction has ended."<<endl;
}

And executing, I get the following output: Creating a being. Destroying a being. Construction has ended. Destroying a being. Destroying a being. Destroying a being. Destroying a being. Destroying a being. Where I was expecting the following: Creating a being. Creating a being. Creating a being. Creating a being. Creating a being. Construction has ended. Destroying a being. Destroying a being. Destroying a being. Destroying a being. Destroying a being. Any ideas? Edit: use source tags (click edit to view) - ED. [Edited by - Emmanuel Deloget on August 15, 2007 2:53:04 PM]

Share this post


Link to post
Share on other sites
Advertisement
The vector creates a temporary being, and then creates crit copies (key word being copies: it uses the copy constructor which is, in this case, the default one provided by the compiler, and is why you don't get any output from them being built) of it, after which point this temporary being falls out of scope and is destroyed (as the vector constructor exits). You then print your "construction has ended" message, and the five beings stored in the vector are destroyed.

Share this post


Link to post
Share on other sites
To go into a little more detail: that constructor's argument list is actually (int, being = being()). This gives you the flexibility to initialize the vector with non-default beings; but of course the vector constructor can't just call *any* being constructor (how would you tell it parameters to use? OK, pass them along as well, but - how many are there? We'd need either a hard-coded limit, or a variadic function, and both of those are rather opposed to the principles of the standard library design) - instead, you provide a prototype, which it copies.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
×

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!