You add buttons to a toolbar by filling an array of TBBUTTON structures and specifying the address of the array either in the TB_ADDBUTTONS message or in a call to the CreateToolbarEx function. You can also use the TB_INSERTBUTTON message, which passes the address of a TBBUTTON structure to the toolbar. Each TBBUTTON structure defines the attributes of a button, including the indexes of its string and bitmap as well as its style, state, command identifier, and application-defined 32-bit value.
If you use the CreateWindowEx function to create a toolbar, you must send the TB_BUTTONSTRUCTSIZE message before adding any buttons. The message passes the size of the TBBUTTON structure to the toolbar.