no idea - never used it - but i;m guessing you're trying to get the string representation of the time?
from the docs, GetDate returns a wxDateTime, that exposes a method FormatTime, that returns a wxString, that has a member c_str() that gives you a string
so you want something like
<br />
void wxPanel4Frame::OnbtnBeginClick(wxCommandEvent& event)<br />
{<br />
txtBdate->SetValue(CalendarCtrl1->GetDate().FormatTime(...).c_str());<br />
}<br />