class A2:virtual public Grand
1.构造顺序按派生列表顺序,若有虚基类先构造虚基类,销毁顺序和构造顺序相反。
2.虚基类时,孙子C来初始化爷爷Grand。
附:thinking in c++ 2nd
https://www.micc.unifi.it/bertini/download/programmazione/TICPP-2nd-ed-Vol-one-printed.pdf
http://vergil.chemistry.gatech.edu/resources/programming/pdf/TIC2Vtwo.pdf