c++ - 向上转换空指针是否会导致未定义的行为

Question

我想知道以下代码是否会导致未定义的行为:

#include <cstddef>
#include <cstdio>

struct IA { 
  virtual ~IA() {}
  int a = 0;
};
struct IB {
  virtual ~IB() {}
  int b = 0;
};
struct C: IA, IB {};

int main() {
  C* pc = nullptr;
  IB* pib = pc;
  std::printf("%p %p", (void*)pc, (void*)pib);
}

Answer 1

向上转换一个空指针被定义为给你另一个空指针:

4.10p3:

A prvalue of type "pointer to cv D", where D is a class type, can be converted to a prvalue of type "pointer to cv B", where B is a base class of D. ... The null pointer value is converted to the null pointer value of the destination type.