我不明白為什么在下面的代碼中，當(dāng)我實(shí)例化一個(gè)類型為object的對(duì)象時(shí)daughter，grandmother()會(huì)調(diào)用默認(rèn)構(gòu)造函數(shù)？我認(rèn)為grandmother(int)應(yīng)該調(diào)用構(gòu)造函數(shù)（以遵循我的mother類構(gòu)造函數(shù)的規(guī)范），或者由于虛擬繼承而根本不應(yīng)該編譯此代碼。在這里，編譯器grandmother在我的背后默默地調(diào)用默認(rèn)構(gòu)造函數(shù)，而我從未要求過(guò)它。#include <iostream>class grandmother {public:    grandmother() {        std::cout << "grandmother (default)" << std::endl;    }    grandmother(int attr) {        std::cout << "grandmother: " << attr << std::endl;    }};class mother: virtual public grandmother {public:    mother(int attr) : grandmother(attr) {        std::cout << "mother: " << attr << std::endl;    }};class daughter: virtual public mother {public:    daughter(int attr) : mother(attr) {        std::cout << "daughter: " << attr << std::endl;    }};int main() {  daughter x(0);}