访问类中的指针向量

Question

I'm trying to figure out a way to keep track of all the instances of a class I have made, so I can access them at any point using a title string (or int ID)

I decided to use a static vector of pointers to each instance, and then on creating each instance i'd add a pointer to it to the vector.

This works up to a point but at one point the values inside each element of the vector seem to reset/get randomly assigned values and i can't figure out what's happening.

i'm adding the object to the vector here:

SWindow::SWindow(LPCWSTR WindowClass, LPCWSTR Title, UINT Style, int x, int y, int height, int width, HWND hParWnd, HINSTANCE hInstance)
    :
    x(x),
    y(y)
{
    hWnd = CreateWindowEx(NULL, WindowClass, Title, Style, x, y, height, width, hParWnd, NULL, hInstance, NULL);
    SWindows.push_back(this);

The function at which the values change is: which is a member of the SWindow class

SWindow.h:

static SWindow* GetSWindow(wstring ws);

SWindow.cpp:

 SWindow* SWindow::GetSWindow(wstring ws)
{
    for (int i = 0; i < SWindow::SWindows.size(); i++)
    {
        if (SWindows[i]->title == ws)
        {
            return SWindows[i];
        }
        else
        {
        }
    }

    return 0;
}

i'm accessing the function from a different class using:

SWindow* pPlayViewer = SWindow::GetSWindow(L"Viewer");

Also if this is a bad way to be doing what i am trying to do, let me know of a better way. Thanks!

Answer 1

Are you sure that you didn't add stack allocated objects into your static vector? Did you remove pointers when objects are deleted ?

If you want to be more efficient, I can suggest you to use a map, where the key can be your title string/id int and the value the pointer, so that the search would be much faster than parsing the whole array.

Answer 2

There are four main possible causes for the dangling pointers:

• you do not remove the instances from the vector upon destruction of an instance

• you create instances accross DLL boundaries (and pass the vector arround)

• you have a buffer overflow (or similar) in another part of the code and it is overwriting your vector

• you are accessing the vector concurrently from multiple threads (and the access to it doesn't look synchronized in your code)

(this is all speculation on my part).

To use such a vector correctly, you will have to do the following:

• implement all constructors and destructor for your class (this implies you will also implement the assignment operators, according to the rule of five).

• ensure all constructors add this to the vector

• ensure destructor removes this from the vector

Also, suggested refactorings:

• pass the vector into the object, instead of declaring it as static; this will allow you to decide in client code if you have a single vector, multiple ones, or a window manager object of some sort, that holds a vector internally

• group the window creation parameters into a structure, and pass that arround as a parameter

• your SWindow class wants to be both a window manager and a window; Extract the window management into a separate object