BBC BASIC Programmers' Reference

Moving the cursor in an edit control

by Richard Russell, November 2007

Windows doesn't provide an explicit method for moving the text cursor (caret) in an Edit Control, however it is easy to achieve the same result using a side effect of the EM_SETSEL message. The principal purpose of that message is to select a range of text, under program control, but as well as selecting the text the Edit Control moves the caret to the end of the selection. So by selecting an empty range, where the start of the selection and the end of the selection are in the same place, the effect is simply to move the caret.

For an Edit Control in a dialogue box you would do that as follows:

        EM_SETSEL = 177
        SYS "SendDlgItemMessage", !dlg%, id%, EM_SETSEL, cpos%, cpos%

where dlg% is the value returned from FN_newdialog, id% is the ID number of the Edit Control and cpos% is the offset into the text where you want the caret to be moved.

Similarly for an Edit Control in your main window you would do:

        EM_SETSEL = 177
        SYS "SendMessage", hEdit%, EM_SETSEL, cpos%, cpos%

where hEdit% is the window handle of the Edit Control, typically as returned from FN_createwindow.

To move the cursor to the end of the text (when you don't know its exact length) you can select the entire text (which moves the insertion point to the end) and then remove the selection. For an Edit Control in a dialogue box do that as follows:

        EM_SETSEL = 177
        SYS "SendDlgItemMessage", !dlg%, id%, EM_SETSEL, 0, -1  : REM Select the entire text
        SYS "SendDlgItemMessage", !dlg%, id%, EM_SETSEL, -1, -1 : REM Remove the selection

For an edit box in your main window:

        EM_SETSEL = 177
        SYS "SendMessage", hEdit%, EM_SETSEL, 0, -1  : REM Select the entire text
        SYS "SendMessage", hEdit%, EM_SETSEL, -1, -1 : REM Remove the selection

Having moved the cursor to the end (and removed any selection) you can append some new text as follows:

       EM_REPLACESEL = 194
       SYS "SendDlgItemMessage", !dlg%, id%, EM_REPLACESEL, 0, "Additional Text"

or for a an edit box in the main window:

       EM_REPLACESEL = 194
       SYS "SendMessage", hEdit%, EM_REPLACESEL, 0, "Additional Text"