空指针与 int 等价
Bjarne 在《C++ 编程语言》中写道，空指针与整数零不同，但 0 可以用作空指针的指针初始值设定项。这是否意味着：
void * voidPointer = 0;
int zero = 0;
int castPointer = reinterpret_cast<int>(voidPointer);
assert(zero == castPointer) // this isn't necessarily true
In "The C++ Programming Language", Bjarne writes that the null pointer is not the same as the integer zero, but instead 0 can be used as an pointer initializer for a null pointer. Does this mean that:
void * voidPointer = 0;
int zero = 0;
int castPointer = reinterpret_cast<int>(voidPointer);
assert(zero == castPointer) // this isn't necessarily true
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是的，这意味着
castPointer不一定为零，并且断言可能会失败。因为虽然空指针常量为零，但某些类型的空指针不一定是所有位都为零的地址。在将空指针转换为 int 时，reinterpret_cast 没有特殊的规定来产生零。您可以通过使用布尔运算符来实现此目的，该运算符将使用
0或1初始化变量：Yes, that means that
castPointerisn't necessarily zero, and the assert may fail. Because while the null pointer constant is zero, the null pointer of some type is not necessarily an address with all bits zero.reinterpret_casthas no special provisions to yield zero when casting a null pointer to int. You can achieve that by using boolean operators, which will initialize the variable with either0or1: