我在A类中加了发送消息的函数，在B类中写了触发消息的按钮，
A类
void CMFCApplication2Dlg::GetBirthday() {
char* birthday = "7.17";
::SendMessage(CBirthdayDlg::hwnd,WM_MyMessage, 0, LPARAM(birthday));
}
B类
CMFCApplication2Dlg *birthday=new CMFCApplication2Dlg();
birthday->GetBirthday();
}