The window procedure for a toolbar automatically sets the size and position of the toolbar window. The height is based on the height of the buttons in the toolbar. The width is the same as the width of the parent window's client area. The CCS_TOP and CCS_BOTTOM common control styles determine whether the toolbar is positioned along the top or bottom of the client area. By default, a toolbar has the CCS_TOP style.
The toolbar window procedure automatically adjusts the size of the toolbar whenever it receives a WM_SIZE or TB_AUTOSIZE message. An application should send either of these messages whenever the size of the parent window changes or after sending a message that requires the size of the toolbar to be adjusted ¾ for example, the TB_SETBUTTONSIZE message.