jrtplib example3程序问题

看了example1和example2程序都是可以理解的，现在再看example3，以前对C++用的较少感觉有问题不好理解

继承类MyRTPSession中的三个函数明明在main函数中没有调用，但是为什么在后台运行了呢，为什么可以自动添加AddDestination，希望看到的博友给解释一下，谢谢！

#include "rtpsession.h"

#include "rtppacket.h"

#include "rtpudpv4transmitter.h"

#include "rtpipv4address.h"

#include "rtpsessionparams.h"

#include "rtperrors.h"

#ifndef WIN32

#include <netinet/in.h>

#include <arpa/inet.h>

#else

#include <winsock2.h>

#endif // WIN32

#include "rtpsourcedata.h"

#include <stdlib.h>

#include <stdio.h>

#include <iostream>

#include <string>

using namespace jrtplib;

//

// This function checks if there was a RTP error. If so, it displays an error

// message and exists.

//

void checkerror(int rtperr)

{

if (rtperr < 0)

{

std::cout << "ERROR: " << RTPGetErrorString(rtperr) << std::endl;

exit(-1);

}

}

//

// The new class routine

//

class MyRTPSession : public RTPSession

{

protected:

void OnNewSource(RTPSourceData *dat)

{

if (dat->IsOwnSSRC())

return;

uint32_t ip;

uint16_t port;

if (dat->GetRTPDataAddress() != 0)

{

const RTPIPv4Address *addr = (const RTPIPv4Address *)(dat->GetRTPDataAddress());

ip = addr->GetIP();

port = addr->GetPort();

}

else if (dat->GetRTCPDataAddress() != 0)

{

const RTPIPv4Address *addr = (const RTPIPv4Address *)(dat->GetRTCPDataAddress());

ip = addr->GetIP();

port = addr->GetPort()-1;

}

else

return;

RTPIPv4Address dest(ip,port);

AddDestination(dest);

struct in_addr inaddr;

inaddr.s_addr = htonl(ip);

std::cout << "Adding destination " << std::string(inet_ntoa(inaddr)) << ":" << port << std::endl;

}

void OnBYEPacket(RTPSourceData *dat)

{

if (dat->IsOwnSSRC())

return;

uint32_t ip;

uint16_t port;

if (dat->GetRTPDataAddress() != 0)

{

const RTPIPv4Address *addr = (const RTPIPv4Address *)(dat->GetRTPDataAddress());

ip = addr->GetIP();

port = addr->GetPort();

}

else if (dat->GetRTCPDataAddress() != 0)

{

const RTPIPv4Address *addr = (const RTPIPv4Address *)(dat->GetRTCPDataAddress());

ip = addr->GetIP();

port = addr->GetPort()-1;

}

else

return;

RTPIPv4Address dest(ip,port);

DeleteDestination(dest);

struct in_addr inaddr;

inaddr.s_addr = htonl(ip);

std::cout << "Deleting destination " << std::string(inet_ntoa(inaddr)) << ":" << port << std::endl;

}

void OnRemoveSource(RTPSourceData *dat)

{

if (dat->IsOwnSSRC())

return;

if (dat->ReceivedBYE())

return;

uint32_t ip;

uint16_t port;

if (dat->GetRTPDataAddress() != 0)

{

const RTPIPv4Address *addr = (const RTPIPv4Address *)(dat->GetRTPDataAddress());

ip = addr->GetIP();

port = addr->GetPort();

}

else if (dat->GetRTCPDataAddress() != 0)

{

const RTPIPv4Address *addr = (const RTPIPv4Address *)(dat->GetRTCPDataAddress());

ip = addr->GetIP();

port = addr->GetPort()-1;

}

else

return;

RTPIPv4Address dest(ip,port);

DeleteDestination(dest);

struct in_addr inaddr;

inaddr.s_addr = htonl(ip);

std::cout << "Deleting destination " << std::string(inet_ntoa(inaddr)) << ":" << port << std::endl;

}

};

//

// The main routine

// 

int main(void)

{

#ifdef WIN32

WSADATA dat;

WSAStartup(MAKEWORD(2,2),&dat);

#endif // WIN32

MyRTPSession sess;

uint16_t portbase;

std::string ipstr;

int status,i,num;

        // First, we'll ask for the necessary information

std::cout << "Enter local portbase:" << std::endl;

std::cin >> portbase;

std::cout << std::endl;

std::cout << std::endl;

std::cout << "Number of seconds you wish to wait:" << std::endl;

std::cin >> num;

// Now, we'll create a RTP session, set the destination

// and poll for incoming data.

RTPUDPv4TransmissionParams transparams;

RTPSessionParams sessparams;

// IMPORTANT: The local timestamp unit MUST be set, otherwise

//            RTCP Sender Report info will be calculated wrong

// In this case, we'll be just use 8000 samples per second.

sessparams.SetOwnTimestampUnit(1.0/8000.0);

sessparams.SetAcceptOwnPackets(true);

transparams.SetPortbase(portbase);

status = sess.Create(sessparams,&transparams);

checkerror(status);

for (i = 1 ; i <= num ; i++)

{

sess.BeginDataAccess();

// check incoming packets

if (sess.GotoFirstSourceWithData())

{

do

{

RTPPacket *pack;

while ((pack = sess.GetNextPacket()) != NULL)

{

// You can examine the data here

printf("Got packet !\n");

// we don't longer need the packet, so

// we'll delete it

sess.DeletePacket(pack);

}

} while (sess.GotoNextSourceWithData());

}

sess.EndDataAccess();

#ifndef RTP_SUPPORT_THREAD

status = sess.Poll();

checkerror(status);

#endif // RTP_SUPPORT_THREAD

RTPTime::Wait(RTPTime(1,0));

}

sess.BYEDestroy(RTPTime(10,0),0,0);

#ifdef WIN32

WSACleanup();

#endif // WIN32

return 0;

}