来自构造函数的 C++ 虚函数

为什么下面的示例打印0"，并且必须改变什么才能像我预期的那样打印1"?

#include <iostream>
struct base {
   virtual const int value() const {
      return 0;
   }
   base() {
      std::cout << value() << std::endl;
   }
   virtual ~base() {}
};

struct derived : public base {
   virtual const int value() const {
      return 1;
   }
};

int main(void) {
   derived example;
}

推荐答案

因为 base 是先构造的，还没有成熟"成 derived.当它不能保证对象已经正确初始化时，它不能调用对象的方法.

Because base is constructed first and hasn't "matured" into a derived yet. It can't call methods on an object when it can't guarantee that the object is already properly initialized.