This function returns the identifier of the specified control.
The identifier of the control indicates success. Zero indicates failure. An invalid value for the hwndCtl parameter, for example, will cause the function to fail. To get extended error information, call GetLastError.
Identifiers are only valid for child windows. An application sets the identifier by passing it in as the hMenu parameter to the CreateWindowEx function. It can also be set and retrieved by calling the SetWindowLong and GetWindowLong functions with the nIndex parameter set to GWL_ID.
Although GetDlgCtrlID may return a value if hwndCtl identifies a top-level window, top-level windows cannot have identifiers and such a return value is never valid.