【正文】 answer is NULL. (not allowed for 2XX)answer The sip answer to send.inteXosip_call_terminate( int cid,int did)Terminate a call. send CANCEL, BYE or 603 Decline.Parameters:cid call id of call.did dialog id of call.inteXosip_call_build_prack(inttid,osip_message_t **prack)Build a PRACK for invite.Parameters:tid id of the invite transaction.prack The sip prack to build.inteXosip_call_send_prack(inttid,osip_message_t *prack)Send a PRACK for invite.Parameters:tid id of the invite transaction.prack The sip prack to send.inteXosip_transfer_send_notify(intdid,int subscription_status,char*body)Send a NOTIFY containing the information about a call transfer.THIS METHOD WILL BE REPLACED or REMOVED, please use the new API to buildNOTIFY.Parameters:did dialog id of call.subscription_status the subscription status.body the body to attach to NOTIFY.inteXosip_call_get_referto(int did,char*refer_to,size_trefer_to_len)Get ReferTo header with Replace parameter from dialog.Parameters:did id of the dialog.refer_to buffer to be filled with referto info.refer_to_len size of refer_to buffer. eXosip2 request outside of dialog Functionsint eXosip_message_build_request (osip_message_t **message, const char *method, constchar *to, const char *from, const char *route)int eXosip_message_send_request (osip_message_t *message)int eXosip_message_build_answer (int tid, int status, osip_message_t **answer)int eXosip_message_send_answer (int tid, int status, osip_message_t *answer) Function DocumentationinteXosip_message_build_request(osip_message_t ** message,const char*method,const char*to,const char*from,const char*route)Build a default request message.This method will be updated to send any message outside of dialog In this later case, you39。}eXosip_register_send_register (id, reg)。i = eXosip_register_build_register (id, 1800, amp。return i。}osip_message_set_supported (reg, 100rel)。id = eXosip_register_build_initial_register (identity, registrar,NULL,1800, amp。 HowTo send or update registrations.eXosip2 offers a flexible API to help you to register one or several identities. Initiate a registrationTo start a registration, you need to build a default REGISTER request bby providingseveral mandatory headersosip_message_t *reg = NULL。osip_message_set_content_type (info, application/dtmfrelay)。eXosip_lock ()。ll usually need to insert a SDP body in the answerand before this, to negotiate the parameters and codecs that you want to support. Inthe test tool, provided by eXosip2 (josua application), you39。eXosip_call_send_answer (catid, 415, NULL)。answer)。Note: The above code also shows that the stack is sometimes able to build and senda default SIP messages with only one API callThen, when the user wants to answer the call, you39。ll get your pointer back in eXosip_event. Answer a callThe code below is another example that teach you how to answer an ining call.You39。}eXosip_unlock ()。osip_message_set_content_type (invite, application/sdp)。char localip[128]。invite,sip:to,sip:from,NULL, // optionnal route headerThis is a call for aconversation)。referto_head)。if (jetype == EXOSIP_CALL_NEW){........}else if (jetype == EXOSIP_CALL_ACK){........}else if (jetype == EXOSIP_CALL_ANSWERED){........}else .............eXosip_event_free(je)。eXosip_lock()。}... then you have to send messages and wait for eXosip events...In the previous code, you39。i = eXosip_listen_addr (IPPROTO_UDP, NULL, port, AF_INET, 0)。exoSip 開(kāi)發(fā)者手冊(cè)——本手冊(cè)指導(dǎo)開(kāi)發(fā)者利用exoSip 棧開(kāi)發(fā)用戶代理原文標(biāo)題：exoSIP User Manual1 The eXtented eXosip stack.............................................................................................................4 HowTo initialize libeXosip2........................................................................................4 HowTo initiate, modify or terminate calls. ..................................................................5 Initiate a call......................................................................................................6 Answer a call.....................................................................................................7 Sending other request........................................................................................8 HowTo send or update registrations. ...........................................................................9 Initiate a registration .........................................................................................9 Update a registration .........................................................................................9 Closing the registration ...................................................................................102 General purpose API ...............................................................................................................11 eXosip2 configuration API..........................................................................................11 Functions.......................................................................................................................11 Function Documentation.................................................................................11 eXosip2 network API ..................................................................................................14 Functions.........................................................................................................14 Function Documentation.................................................................................14 eXosip2 event API ............................................................................................................16 Data Structures........................................