lineAddToConference function (tapi.h)

The lineAddToConference function adds the call specified by hConsultCall to the conference call specified by hConfCall.


LONG lineAddToConference(
  HCALL hConfCall,
  HCALL hConsultCall



Handle to the conference call. The application must be an owner of this call. Any monitoring (media, tones, digits) on a conference call applies only to the hConfCall, not to the individual participating calls. Call state of hConfCall must be onHoldPendingConference or onHold.


Handle to the call to be added to the conference call. The application must be an owner of this call. This call cannot be a parent of another conference or a participant in any conference. Depending on the device capabilities indicated in LINEADDRESSCAPS, the hConsultCall may not necessarily have been established using lineSetupConference or linePrepareAddToConference. The call state of hConsultCall must be connected, onHold, proceeding, or ringback. Many PBXs allow calls to be added to conferences before they are actually answered.

Return value

Returns a positive request identifier if the function is completed asynchronously, or a negative error number if an error occurs. The dwParam2 parameter of the corresponding LINE_REPLY message is zero if the function succeeds, or it is a negative error number if an error occurs. Possible return values are:



If LINEERR_INVALCALLHANDLE is returned, the specified call handle for the added call is invalid; hConsultCall is a parent of another conference or already a participant in a conference; hConsultCall cannot be added for other reasons (such as, it must have been established using lineSetupConference or linePrepareAddToConference); or hConsultCall and hConfCall are calls on different open lines.

The call handle of the added party remains valid after adding the call to a conference. Its state typically changes to conferenced while the state of the conference call typically becomes connected. Using lineGetConfRelatedCalls, you can obtain a list of call handles that are part of the same conference call as the specified call. The specified call is either a conference call or a participant call in a conference call. New handles are generated for those calls for which the application does not already have handles, and the application is granted monitor privilege to those calls. The handle to an individual participating call can be used later to remove that party from the conference call using lineRemoveFromConference.

If lineGetConfRelatedCalls is called immediately after lineAddToConference, it may not return a complete list of related calls because TAPI waits to receive a LINE_CALLSTATE message indicating that the call has entered LINECALLSTATE_CONFERENCED before it considers the call to actually be part of the conference (that is, the conferenced state is confirmed by the service provider). After the application has received the LINE_CALLSTATE message, lineGetConfRelatedCalls returns complete information.

Note  All calls that are part of a conference must exist on the same open line.
The call states of the calls participating in a conference are not independent. For example, when dropping a conference call, all participating calls can automatically become idle. An application should consult the line's device capabilities to determine what form of conference removal is available. The application should track the LINE_CALLSTATE messages to determine what happened to the calls involved.

The conference call is established either by lineSetupConference or lineCompleteTransfer. The call added to a conference is typically established using lineSetupConference or linePrepareAddToConference. Some switches can allow adding arbitrary calls to the conference, and such a call can have been set up using lineMakeCall and be on (hard) hold. The application can examine the dwAddrCapFlags member of the LINEADDRESSCAPS structure to determine the permitted operations.


Target Platform Windows
Header tapi.h
Library Tapi32.lib
DLL Tapi32.dll

See also

Conference overview



Supplementary Line Service Functions