c++ - 当您将位移超出变量的末尾时会发生什么？

Question

如果你有一些变量(在堆栈上)并且你向左或向右移动超出其末尾会发生什么？

即

byte x = 1;
x >> N;

如果 x 是指向内存的指针并转换为字节，而您做同样的事情会怎样？

byte* x = obtain pointer from somewhere;
*x = 1;
*x >> N;

Answer 1

它不会(必然)变为零。行为未定义(C99 §6.5.7，“移位运算符”):

If the value of the right operand is negative or is greater than or equal to the width of the promoted left operand, the behavior is undefined.

(C++0x §5.8，“移位运算符”):

The behavior is undefined if the right operand is negative, or greater than or equal to the length in bits of the promoted left operand.

被转移的值的存储对此没有任何影响。