question about vectors

[bahoo]

Hi,

In the main function, I have

vector<vector<Store>stores;
vector<Storev(11);
stores.push_back(v);

and here is the Store class:

class Store
{
public:
Store();
IplImage* img;
};

Store::Store()
{
img = cvCreateImage(cvSize(512,512), IPL_DEPTH_32F, 1);
}

The strange thing is that all the 11 "v" have the same "img", with the
same address in the memory. What I wanted is of course 11 "v" with
different "img".

Can anyone spot the error?
Thanks
bahoo

[Kira Yamato]

On 2007-12-21 23:58:12 -0500, bahoo <b8*******@yahoo.comsaid:

Hi,

In the main function, I have

vector<vector<Store>stores;
vector<Storev(11);
stores.push_back(v);

and here is the Store class:

class Store
{
public:
Store();
IplImage* img;
};

Store::Store()
{
img = cvCreateImage(cvSize(512,512), IPL_DEPTH_32F, 1);
}

The strange thing is that all the 11 "v" have the same "img", with the
same address in the memory. What I wanted is of course 11 "v" with
different "img".

Can anyone spot the error?
Thanks
bahoo

I just found this out myself. It turns out that the way std::vector
initializes its array is this:
1) create a default object,
2) use the copy constructor to create all the elements of the array.

In your case, it created one copy of the default Store object. Then
the copy constructor simply made 11 copies each copying from the same
img pointer value.

So maybe you should do this instead:

vector<Storev;
for(int i = 0; i < 11; i++) v.push_back(Store());

--

-kira

[Daniel T.]

On Dec 21, 11:58*pm, bahoo <[e-mail]:

Hi,

In the main function, I have

vector<vector<Store>stores;
vector<Storev(11);
stores.push_back(v);

and here is the Store class:

class Store
{
public:
* * * * Store();
* * * * IplImage* img;

};

Store::Store()
{
* * * * img = cvCreateImage(cvSize(512,512), IPL_DEPTH_32F, 1);

}

The strange thing is that all the 11 "v" have the same "img", with the
same address in the memory. What I wanted is of course 11 "v" with
different "img".

Can anyone spot the error?

The error is that you don't have a correct copy constructor and
assignment op in your class. The vector uses the defaults wich don't
do what you want. I expect that your Store class had a destructor
(though you didn't post the code here.) Anytime a class needs a custom
destructor, it is very likely it needs a custom assignment operator
and copy constructor as well.

The proper solution is to write a copy constructor for your class.