关于在CALLBACK Wndproc中静态变量的问题

Question

代码如下：为为什么N的值不是从编辑框中输入的值呢？？

 LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static int N;
    static HWND hEdit,hButton;
  char szBuffer[10];
    HDC hdc;
    PAINTSTRUCT ps;

    switch (message)
    {
    case WM_CREATE:
        hEdit = CreateWindow(TEXT("edit"), 
            NULL, WS_CHILD | WS_VISIBLE|WS_BORDER, 
            0,0,0,0,
            hwnd, (HMENU)ID_EDIT, ((LPCREATESTRUCT)lParam)->hInstance, NULL);
        hButton = CreateWindow(TEXT("Button"),
            TEXT("Button"), WS_CHILD | WS_VISIBLE,
            500, 300, 
            7* cxChar, 2 * cyChar, 
            hwnd, (HMENU)ID_Button,((LPCREATESTRUCT)lParam)->hInstance, NULL);
        return 0;
    case WM_SIZE:
        MoveWindow(hEdit, cxClient - 100, 2 * cyChar,
            10 * cxChar, 2* cyChar, TRUE);
        return 0;
    case WM_COMMAND:    
        switch (LOWORD(wParam))
        {
        case 1:
            //SetFocus(hEdit);
        GetDlgItemText(hwnd, ID_EDIT, szBuffer, TRUE);
        N=atof(szBuffer);
            break;
        case 2:
            InvalidateRect(hwnd, NULL, TRUE);
            break;
        }
        return 0;

Answer 1

CWnd::GetDlgItemInt

http://msdn.microsoft.com/zh-cn/library/c7t43w0s.aspx

它将指定控件的文本在特定对话框的转换为整数值通过去除所有多余空格在该文本的开头和转换十进制数字。 在到达结尾的文本或遇到任何非数值字符时，终止平移。