c#调用GetWindowText函数

[DllImport("user32.dll")]
        public static extern int GetWindowTextLength(IntPtr hWnd);

[DllImport("User32.dll", CharSet = CharSet.Auto)]
        public static extern int GetWindowText(IntPtr hWnd, StringBuilder text, int nMaxCount);
int length = GetWindowTextLength(hWnd);
            StringBuilder windowName = new StringBuilder(length + 1);
            GetWindowText(hWnd, windowName, windowName.Capacity);

用DllImport声明GetWindowText时，千万别跟第2个参数加out。