基类函数的this指针和派生类函数的this指针

在研究live555流程代码时，因为遇到对于基类RTSPServer在函数createNewClientConnection中，创建RTSPClientConnection时，采用的是new RTSPClientConnection(*this, clientSocket, clientAddr)方法创建的RTSPClientConnection，而在live media server中DynamicRTSPServer继承自RTSPServer，而主程序中只创建了DynamicRTSPServer对象；百思不得解，在此处创建RTSPClientConnection时，给其传递的是this指针的内容，而在其构造函数中，代码如下：

RTSPServer::RTSPClientConnection::RTSPClientConnection(RTSPServer& ourServer, int clientSocket, struct sockaddr_in clientAddr)  : fOurServer(ourServer), fIsActive(True),    fClientInputSocket(clientSocket), fClientOutputSocket(clientSocket), fClientAddr(clientAddr),    fRecursionCount(0), fOurSessionCookie(NULL) {  // Add ourself to our 'client connections' table:  fOurServer.fClientConnections->Add((char const*)this, this);  // Arrange to handle incoming requests:  resetRequestBuffer();  envir().taskScheduler().setBackgroundHandling(fClientInputSocket, SOCKET_READABLE|SOCKET_EXCEPTION,(TaskScheduler::BackgroundHandlerProc*)&incomingRequestHandler, this);}

this指针的传递和构造函数的初始化列表都显示fOurServer赋值为RTSPServer的this指针，而在handleCmd_DESCRIBE函数中

ServerMediaSession* session = fOurServer.lookupServerMediaSession(urlTotalSuffix);

的调用为什么能够调到DynamicRTSPServer::lookupServerMediaSession(char const* streamName)函数呢，在此不得以对this指针在基类和派生类的赋值进行了研究，结论表明：在派生类继承基类的时候，派生类初始化的时候调用基类的构造函数，随后调用派生类的构造函数，基类构造函数的this指针指向的是派生类对象，因为其this指针的值和派生类this指针的值相同，一下为我自己写的测试代码：

//MyTest.h文件#ifndef _MY_TEST_H#define _MY_TEST_Hclass BaseTest{public:BaseTest(int fun);virtual ~BaseTest();static BaseTest* CreateNew(int fun);void show();virtual void getInfo();private:int num;};class DeriveTest: public BaseTest{public:DeriveTest(int num, int func);virtual ~DeriveTest();static DeriveTest* CreateNew(int num,int func);void show();virtual void getInfo();private:int fun;};#endif

//MyTest.cpp文件#include <iostream>#include "MyTest.h"using namespace std;BaseTest::BaseTest(int num):num(num){cout<<"the point base is:"<<this<<endl;}BaseTest::~BaseTest(){}BaseTest* BaseTest::CreateNew(int num){return new BaseTest(num);}void BaseTest::show(){cout<<"this is BaseTest!"<<endl;getInfo();}void BaseTest::getInfo(){cout<<"the point is:"<<this<<endl;}DeriveTest::DeriveTest(int num, int func):BaseTest(num),fun(func){cout<<"the point derive is:"<<this<<endl;}DeriveTest::~DeriveTest(){}DeriveTest* DeriveTest::CreateNew(int num, int func){return new DeriveTest(num, func);}void DeriveTest::show(){cout<<"this is DeriveTest!"<<endl;}void DeriveTest::getInfo(){cout<<"the point1 is:"<<this<<endl;}

 

//测试main函数文件#include "MyTest.h"int main(){int num = 5;int fun = 10;BaseTest *myTest = DeriveTest::CreateNew(5,10);return 0;}

测试结果显示为：

the point base is:00032BC8
the point derive is:00032BC8

通过剪短的测试，明白了在初始化时赋值的this指针的作用，也明白了live555在内部调用和设计的复杂性，加油，得进一步努力分析代码了。