sending enter key message to window

I have the handle names of a edit box which is a child of a combo box. these two controls are in another application.

using:

Code:

SendMessage(txtBox, WM_SETTEXT, NULL, (LPARAM)(LPCTSTR)response);

I can place text in the edit box. Now i need to send the enter key message to the edit box, I have tried:

Code:

SendMessage(txtBox, WM_KEYDOWN, VK_RETURN, 0);
SendMessage(txtBox, WM_KEYUP,  VK_RETURN, 0);

Code:

PostMessage(txtBox, WM_CHAR, VK_RETURN, 0);

Code:

SendMessage(txtBox, WM_CHAR, VK_RETURN, 0);

Code:

PostMessage(txtBox, WM_KEYDOWN, VK_RETURN, 0);
PostMessage(txtBox, WM_KEYUP, VK_RETURN, 0);

Code:

keybd_event(VK_RETURN, 0,0,0);
keybd_event(13, 0,KEYEVENTF_KEYUP,0);

None of which worked. I use Borland C++ 3, Win 2000

Any ideas?
thanks

1. Just a tip, it's probably better to prefix handle names with 'h'. It just allows you to tell that it's a handle straight away.

2. I think you may have to send the enter message to a different part of the control. Normally, single-line edit controls don't receive enter key messages, they're redirected elsewhere. Try sending it to the overall control.

You should understand the difference between notifications and actual events. Most of the messages you are attempting to send to the control are notifications. These are messages that are sent to windows after something has happened. It notifies them, in case they wish to do something in response to it. They do not emulate the event which has happened.

As an example, the SetFocus() function changes the focus, whereas WM_KILLFOCUS is simply a notification to tell that window that the focus has been lost. It cannot be sent to force it to lose focus.