指针指向不正确？

Question

I am running this code in a thread, assuming receivedPosts and td->window are valid:

std::vector<Post> *receivedPosts_n = new std::vector<Post>;
*receivedPosts_n = receivedPosts;

SendMessage(td->window, WM_TIMER, IDT_TIMER_FIND_NEW_POSTS_CALLBACK, 
    (LPARAM) receivedPosts_n);

I'm running this code at IDT_TIMER_FIND_NEW_POSTS_CALLBACK (hwnd is td->window):

case IDT_TIMER_FIND_NEW_POSTS_CALLBACK:
    {
        std::vector<Post> *currentPosts_ptr = (std::vector<Post> *)lParam;

        //This vector turns up as undefined
        std::vector<Post> currentPosts = *currentPosts_ptr;
    }
    break;

But the problem is that *currentPosts_ptr turns up as an invalid pointer, ie it points to random memory.

What is wrong with the pointer?

Thanks.

Answer 1

MSDN documentation says that for WM_TIMER message value of lParam is

A pointer to an application-defined callback function that was passed to the SetTimer function when the timer was installed.

If you need to send custom messages it is much better idea just to use WM_USER through 0x7FFF that were specially designed for this scenario.