MFC C++ 有关接口调用函数的几个问题

Question

希望能够一句一句的解释，谢谢各位大神了。
HMODULE hDll =( HMODULE )LoadLibrary( "COMObj.dll" );
MYCREATEINSTANCE MyCreate = (
    MYCREATEINSTANCE )GetProcAddress( hDll,"MyCreateInstance" );
IUnknown * piUnknown = MyCreate();
IMath * piMath = NULL;
piUnknown->QueryInterface(IID_IMath,(LPVOID*)&piMath);
piUnknown->Release();
return piMath;

Answer 1

 HMODULE hDll =( HMODULE )LoadLibrary( "COMObj.dll" ); //加载com对象，返回dll的句柄
MYCREATEINSTANCE MyCreate = (
    MYCREATEINSTANCE )GetProcAddress( hDll,"MyCreateInstance" ); 创建MyCreateInstance函数指针的实例，叫MyCreate
IUnknown * piUnknown = MyCreate(); 调用MyCreate函数指针，也就是调用这个函数，创建com对象
IMath * piMath = NULL;
piUnknown->QueryInterface(IID_IMath,(LPVOID*)&piMath); 从IUnknown接口调用QueryInterface得到IMath，IID_IMath是progid
piUnknown->Release(); 释放
return piMath; 返回Math对象指针

QueryInterface进一步介绍
http://www.cnblogs.com/fangyukuan/archive/2010/06/02/1750377.html